Gmsh 1.52

Christophe Geuzaine and Jean-François Remacle

Gmsh is an automatic 3D finite element mesh generator with build-in pre- and post-processing facilities. This is edition 1.20 (July, 27 2004) of the Gmsh Reference Manual, for Gmsh 1.52.

Copying conditions		Terms and conditions of use.
1. Overview		What is Gmsh?
2. General tools		Description of general commands and options.
3. Geometry module		Description of all Geometry commands.
4. Mesh module		Description of all Mesh commands.
5. Solver module		Description of all Solver commands.
6. Post-processing module		Description of all Post-Processing commands.
7. Tutorial		A step-by-step tutorial.
8. Running Gmsh		How to run Gmsh on your operating system.
9. File formats		Input and output file formats.
10. Programming notes		Random notes for developers.
11. Bugs, versions and credits
A. Tips and tricks		Some tips to make your life easier with Gmsh.
B. License		Complete copy of the license.
Concept index		Index of concepts.
Syntax index		Index of reserved keywords in the Gmsh language.

 -- The Detailed Node Listing ---

Overview

1.1 Geometry: geometrical entity definition
1.2 Mesh: finite element mesh generation
1.3 Solver: external solver interface
1.4 Post-processing: scalar, vector and tensor field visualization
1.5 What Gmsh is pretty good at ...
1.6 ... and what Gmsh is not so good at
1.7 Syntactic rules used in this document
1.8 Comments

General tools

2.1 Expressions
2.2 Operators
2.3 Built-in functions
2.4 User-defined functions
2.5 Loops and conditionals
2.6 General commands
2.7 General options

Expressions 

2.1.1 Floating point expressions
2.1.2 Character expressions
2.1.3 Color expressions

Geometry module

3.1 Geometry commands
3.2 Geometry options

Geometry commands

3.1.1 Points
3.1.2 Lines
3.1.3 Surfaces
3.1.4 Volumes
3.1.5 Extrusions
3.1.6 Transformations
3.1.7 Miscellaneous

Mesh module

4.1 Elementary vs. physical entities
4.2 Mesh commands
4.3 Mesh options

Mesh commands

4.2.1 Characteristic lengths
4.2.2 Structured grids
4.2.3 Miscellaneous

Solver module

5.1 Solver options
5.2 Solver example

Post-processing module

6.1 Post-processing commands
6.2 Post-processing plugins
6.3 Post-processing options

Tutorial

7.1 `t1.geo'
7.2 `t2.geo'
7.3 `t3.geo'
7.4 `t4.geo'
7.5 `t5.geo'
7.6 `t6.geo'
7.7 `t7.geo'
7.8 `t8.geo'
7.9 `t9.geo'

Running Gmsh

8.1 Interactive vs. non-interactive mode
8.2 Command-line options
8.3 Mouse actions
8.4 Keyboard shortcuts

File formats

9.1 Gmsh mesh file format
9.2 Gmsh ASCII post-processing file format
9.3 Gmsh binary post-processing file format
9.4 Gmsh parsed post-processing file format
9.5 Gmsh node ordering

Gmsh mesh file format

9.1.1 Version 1.0
9.1.2 Version 2.0

Bugs, versions and credits

11.1 Bugs
11.2 Versions
11.3 Credits

Copying conditions

Gmsh is "free software"; this means that everyone is free to use it and to redistribute it on a free basis. Gmsh is not in the public domain; it is copyrighted and there are restrictions on its distribution, but these restrictions are designed to permit everything that a good cooperating citizen would want to do. What is not allowed is to try to prevent others from further sharing any version of Gmsh that they might get from you.

Specifically, we want to make sure that you have the right to give away copies of Gmsh, that you receive source code or else can get it if you want it, that you can change Gmsh or use pieces of Gmsh in new free programs, and that you know you can do these things.

To make sure that everyone has such rights, we have to forbid you to deprive anyone else of these rights. For example, if you distribute copies of Gmsh, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must tell them their rights.

Also, for our own protection, we must make certain that everyone finds out that there is no warranty for Gmsh. If Gmsh is modified by someone else and passed on, we want their recipients to know that what they have is not what we distributed, so that any problems introduced by others will not reflect on our reputation.

The precise conditions of the license for Gmsh are found in the General Public License that accompanies the source code (see section B. License). Further information about this license is available from the GNU Project webpage http://www.gnu.org/copyleft/gpl-faq.html. Detailed copyright information can be found in 11.3 Credits.

The source code and various pre-compiled versions of Gmsh (for Unix, Windows and Mac OS) can be downloaded from the webpage http://www.geuz.org/gmsh/.

If you use Gmsh, we would appreciate that you mention it in your work. References, as well as the latest news about Gmsh development, are always available on http://www.geuz.org/gmsh/. Please send all Gmsh-related questions to the public Gmsh mailing list at gmsh@geuz.org.

If you want to integrate Gmsh into a closed-source software, or want to sell a modified closed-source version of Gmsh, please contact one of the authors. You can purchase a version of Gmsh under a different license, with "no strings attached" (for example allowing you to take parts of Gmsh and integrate them into your own proprietary code).

1. Overview

Gmsh is an automatic three-dimensional finite element mesh generator, primarily Delaunay, with built-in pre- and post-processing facilities. Its design goal is to provide a simple meshing tool for academic test cases with parametric input and up to date visualization capabilities. One of its strengths is the ability to respect a characteristic length field for the generation of adapted meshes on lines, surfaces and volumes, and to mix these meshes with simple structured (transfinite, extruded, etc.) grids.

Gmsh is built around four modules: geometry, mesh, solver and post-processing. All geometrical, mesh, solver and post-processing instructions are prescribed either interactively using the graphical user interface (GUI) or in ASCII data files using Gmsh's own scripting language. Interactive actions generate language bits in the input files, and vice versa. This makes it possible to automate all treatments, using loops, conditionals and external system calls. A brief description of the four modules is given hereafter.

1.1 Geometry: geometrical entity definition
1.2 Mesh: finite element mesh generation
1.3 Solver: external solver interface
1.4 Post-processing: scalar, vector and tensor field visualization
1.5 What Gmsh is pretty good at ...
1.6 ... and what Gmsh is not so good at
1.7 Syntactic rules used in this document
1.8 Comments

1.1 Geometry: geometrical entity definition

Geometries are created in a bottom-up flow by successively defining points, oriented lines (line segments, circles, ellipses, splines, ...), oriented surfaces (plane surfaces, ruled surfaces, ...) and volumes. Compound groups of geometrical entities can be defined, based on these elementary geometric entities. Gmsh's scripting language allows all geometrical entities to be fully parameterized.

1.2 Mesh: finite element mesh generation

A finite element mesh is a tessellation of a given subset of the three-dimensional space by elementary geometrical elements of various shapes (in Gmsh's case: lines, triangles, quadrangles, tetrahedra, prisms, hexahedra and pyramids), arranged in such a way that if two of them intersect, they do so along a face, an edge or a node, and never otherwise. All the finite element meshes produced by Gmsh are considered as "unstructured", even if they were generated in a "structured" way (e.g. by extrusion). This implies that the elementary geometrical elements are defined only by an ordered list of their nodes but that no predefined order relation is assumed between any two elements.

The mesh generation is performed in the same bottom-up flow as the geometry creation: lines are discretized first; the mesh of the lines is then used to mesh the surfaces; then the mesh of the surfaces is used to mesh the volumes. In this process, the mesh of an entity is only constrained by the mesh of its boundary(1). This automatically assures the conformity of the mesh when, for example, two surfaces share a common line. But this also implies that the discretization of an "isolated" (n-1)-th dimensional entity inside an n-th dimensional entity does not constrain the n-th dimensional mesh. Every meshing step is constrained by the characteristic length field, which can be uniform, specified by characteristic lengths associated with elementary geometrical entities, or associated with another mesh (the background mesh).

For each meshing step, all structured mesh directives are executed first, and serve as additional constraints for the unstructured parts. The implemented Delaunay algorithm is subdivided in the following five steps for surface/volume discretization:

1. trivial meshing of a box including the convex polygon/polyhedron defined by the boundary nodes resulting from the discretization of the lines/surfaces;
2. creation of the initial mesh by insertion of all the nodes on the lines/surfaces thanks to the Bowyer algorithm;
3. boundary restoration to force all the edges/faces of the lines/surfaces to be present in the initial mesh;
4. suppression of all the unwanted triangles/tetrahedra (in particular those containing the nodes of the initial box);
5. insertion of new nodes by the Bowyer algorithm until the characteristic size of each simplex is lower or equal to the characteristic length field evaluated at the center of its circumscribed circle/sphere.

1.3 Solver: external solver interface

External solvers can be interfaced with Gmsh through Unix sockets, which permits to easily launch external computations and to collect and exploit the simulation results within Gmsh's post-processing module. The default solver interfaced with Gmsh is GetDP (http://www.geuz.org/getdp/).

1.4 Post-processing: scalar, vector and tensor field visualization

Multiple post-processing scalar, vector or tensor maps can be loaded and manipulated (globally or individually) along with the geometry and the mesh. Scalar fields are represented by iso-value lines/surfaces or color maps, while vector fields are represented by three-dimensional arrows or displacement maps. Post-processing functions include section computation, offset, elevation, boundary and component extraction, color map and range modification, animation, vector graphic output, etc. All post-processing options can be accessed either interactively or through the input ASCII text files. Scripting permits to automate all post-processing operations, e.g. for the creation of animations. User-defined operations can also be performed on post-processing views through dynamically loadable plugins.

1.5 What Gmsh is pretty good at ...

Gmsh is a (relatively) small program, and was principally developed "in academia, to solve academic problems"... Nevertheless, over the years, many people outside universities have found Gmsh useful in their day-to-day jobs. Here is a tentative list of what Gmsh does best:

• quickly describe simple and/or "repetitive" geometries, thanks to user-defined functions, loops, conditionals and includes (see 2.4 User-defined functions, 2.5 Loops and conditionals, and 2.6 General commands);
• parameterize these geometries. Gmsh's scripting language enables all commands and command arguments to depend on previous calculations (see 2.1 Expressions, and 3.1 Geometry commands);
• generate 1D, 2D and 3D simplicial (i.e. using line segments, triangles and tetrahedra) finite element meshes. The performance of the 1D and 2D algorithms is pretty good; the 3D algorithm is still experimental and slow (see 4. Mesh module, and 7. Tutorial);
• specify target element sizes accurately. Gmsh provides several mechanisms to control the size of the elements in the final mesh: through interpolation from geometrical point characteristic lengths or geometrical attractors, or from user-defined background meshes (see section 4.2 Mesh commands);
• create simple extruded geometries and meshes (see 3.1 Geometry commands, and 4.2 Mesh commands);
• interact with external solvers. Gmsh provides C/C++ and Perl interfaces, and others can be easily added (see section 5. Solver module);
• visualize computational results in a great variety of ways. Gmsh can display scalar, vector and tensor data sets, and can perform various operations on the resulting post-processing views (see section 6. Post-processing module);
• export plots in many different formats: vector PostScript or encapsulated PostScript, LaTeX, PNG, JPEG, ... (see section 2.7 General options);
• generate complex animations (see 2. General tools, and 7.8 `t8.geo');
• run on low end machines and/or machines with no graphic system. Gmsh can be compiled with or without the graphical user interface, and all versions can be used either interactively or not, directly from the command line (see section 8. Running Gmsh);
• configure your preferred options. Gmsh has a large number of configuration options that can be set interactively using the GUI, scattered inside command files, changed on the fly in scripts, set in per-user configuration files, or specified on the command-line (see 2.7 General options, 3.2 Geometry options, 4.3 Mesh options, 6.3 Post-processing options, and 8. Running Gmsh);
• and do all the above on various platforms (Windows, Mac and Unix), for free (see section Copying conditions), using clear-text ASCII files and/or a small but powerful graphical user interface.

1.6 ... and what Gmsh is not so good at

Due to its historical background and limited developer manpower, Gmsh has also some (a lot of?) weaknesses:

• the bottom-up approach for describing geometries can become inconvenient for complex models;
• there is no support for NURBS and only very limited support for trimmed surfaces;
• Gmsh is not primarily a structured mesh generator: no automatic quadrilateral or hexahedral meshing algorithm is provided. If you want quadrangles, you have to use transfinite or extruded meshes or recombine unstructured triangular meshes. For hexahedra, your only choice is transfinite or extruded meshes;
• Gmsh is not a multi-bloc generator: all meshes produced by Gmsh are conforming in the sense of finite element meshes;
• the user has no control over the quality of the mesh elements generated by the 3D unstructured algorithm;
• the 2D anisotropic and the 3D unstructured algorithms are still experimental and not very robust. If these algorithms fail, try to change some characteristic lengths to generate meshes that better suit the geometrical details of the structures;
• Gmsh was designed to solve academic test-cases, not industrial-size problems. You may find that Gmsh is too slow for large problems (with thousands of geometric primitives, or millions of mesh/post-processing elements).

If you have the skills and some free time, feel free to join the project! We gladly accept any code contributions (see section 10. Programming notes) to remedy the aforementioned (and all other) shortcommings...

1.7 Syntactic rules used in this document

Here are the rules we tried to follow when writing this user's guide. Note that metasyntactic variable definitions stay valid throughout the manual (and not only in the sections where the definitions appear).

1. Keywords and literal symbols are printed like this.
2. Metasyntactic variables (i.e. text bits that are not part of the syntax, but stand for other text bits) are printed like this.
3. A colon (:) after a metasyntactic variable separates the variable from its definition.
4. Optional rules are enclosed in < > pairs.
5. Multiple choices are separated by |.
6. Three dots (...) indicate a possible (multiple) repetition of the preceding rule.

1.8 Comments

All Gmsh ASCII text input files support both C and C++ style comments:

1. any text comprised between /* and */ pairs is ignored;
2. the rest of a line after a double slash // is ignored.

These commands won't have the described effects inside double quotes or inside keywords. Also note that `white space' (spaces, tabs, new line characters) is ignored inside all expressions.

2. General tools

This chapter describes the general commands and options that can be used in Gmsh's ASCII text input files. By "general", we mean "not specifically related to one of the geometry, mesh, solver or post-processing modules". Commands peculiar to these modules will be introduced in 3. Geometry module, 4. Mesh module, 5. Solver module, and 6. Post-processing module, respectively.

Note that, if you are just beginning to use Gmsh, or just want to see what Gmsh is all about, you really don't need to read this chapter and the four next ones. Just have a quick look at 8. Running Gmsh, and go play with the graphical user interface, running the tutorials and demonstration files bundled in the distribution! Most of the commands and options described in the following chapters are available interactively in the GUI, so you don't need to worry about Gmsh's internals for creating your first geometries, meshes and post-processing plots. Once you master the tutorial (read the source files: they are heavily commented--see 7. Tutorial), you might want to come back here to learn more about the specific syntax of Gmsh's commands and esoteric options.

2.1 Expressions
2.2 Operators
2.3 Built-in functions
2.4 User-defined functions
2.5 Loops and conditionals
2.6 General commands
2.7 General options

2.1 Expressions

The two constant types used in Gmsh are real and string (there is no integer type). These types have the same meaning and syntax as in the C or C++ programming languages.

2.1.1 Floating point expressions
2.1.2 Character expressions
2.1.3 Color expressions

2.1.1 Floating point expressions

Floating point expressions (or, more simply, "expressions") are denoted by the metasyntactic variable expression (remember the definition of the syntactic rules in 1.7 Syntactic rules used in this document), and are evaluated during the parsing of the data file:

expression: real | string | string [ expression ] | # string [ ] | ( expression ) | operator-unary-left expression | expression operator-unary-right | expression operator-binary expression | expression operator-ternary-left expression operator-ternary-right expression | built-in-function | real-option

Such expressions are used in most of Gmsh's commands. The operators operator-unary-left, operator-unary-right, operator-binary, operator-ternary-left and operator-ternary-right are defined in 2.2 Operators. For the definition of built-in-functions, see 2.3 Built-in functions. The various real-options are listed in 2.7 General options, 3.2 Geometry options, 4.3 Mesh options, 5.1 Solver options, and 6.3 Post-processing options.

List of expressions are also widely used, and are defined as:

expression-list: expression-list-item <, expression-list-item> ...

with

expression-list-item: expression | expression : expression | expression : expression : expression | string [ ] | string [ { expression-list } ] | Point { expression } | transform | extrude

The second case in this last definition permits to create a list containing the range of numbers comprised between two expressions, with a unit incrementation step. The third case also permits to create a list containing the range of numbers comprised between two expressions, but with a positive or negative incrementation step equal to the third expression. The fourth case permits to reference an expression list. The fifth case permits to reference an expression sublist (whose elements are those corresponding to the indices provided by the expression-list). The sixth case permits to retrieve the coordinates of a given geometry point (see section 3.1.1 Points). The last two cases permit to retreive the indices of entities created through geometrical transformations adn extrusions (see 3.1.6 Transformations, and 3.1.5 Extrusions).

To see the practical use of such expressions, have a look at the first couple of examples in 7. Tutorial. Note that, in order to lighten the syntax, you can always omit the braces {} enclosing an expression-list if this expression-list only contains a single item.

2.1.2 Character expressions

Character expressions are defined as:

char-expression: "string" | StrPrefix ( char-expression ) | StrCat ( char-expression , char-expression ) | Sprintf ( char-expression , expression-list ) | char-option

The second case in this definition permits to take the prefix of a string (e.g. for removing the extension from a file name). The third case permits to concatenate two character expressions, and the fourth is an equivalent of the sprintf C function (where char-expression is a format string that can contain floating point formatting characters: %e, %g, etc.). The last case permits to use the value of a char-option as a char-expression. The various char-options are listed in 2.7 General options, 3.2 Geometry options, 4.3 Mesh options, 5.1 Solver options, and 6.3 Post-processing options.

Character expressions are mostly used to specify non-numeric options and input/output file names. See 7.8 `t8.geo', for an interesting usage of char-expressions in an animation script.

2.1.3 Color expressions

Colors expressions are hybrids between fixed-length braced expression-lists and strings:

color-expression: string | { expression, expression, expression } | { expression, expression, expression, expression } | color-option

The first case permits to use the X Windows names to refer to colors, e.g., Red, SpringGreen, LavenderBlush3, ... (see `Common/Colors.h' in Gmsh's source tree for a complete list). The second case permits to define colors by using three expressions to specify their red, green and blue components (with values comprised between 0 and 255). The third case permits to define colors by using their red, green and blue color components as well as their alpha channel. The last case permits to use the value of a color-option as a color-expression. The various color-options are listed in 2.7 General options, 3.2 Geometry options, 4.3 Mesh options, 5.1 Solver options, and 6.3 Post-processing options.

See 7.3 `t3.geo', for an example of the use of color expressions.

2.2 Operators

Gmsh's operators are similar to the corresponding operators in C and C++. Here is the list of the unary, binary and ternary operators currently implemented.

operator-unary-left:

-

Unary minus.

!

Logical not.

operator-unary-right:

++

Post-incrementation.

--

Post-decrementation.

operator-binary:

^

Exponentiation.

*

Multiplication.

/

Division.

%

Modulo.

+

Addition.

-

Subtraction.

==

Equality.

!=

Inequality.

>

Greater.

>=

Greater or equality.

<

Less.

<=

Less or equality.

&&

Logical `and'.

||

Logical `or'. (Warning: the logical `or' always implies the evaluation of both arguments. That is, unlike in C or C++, the second operand of || is evaluated even if the first one is true).

operator-ternary-left:

?

:

The only ternary operator, formed by operator-ternary-left and operator-ternary-right, returns the value of its second argument if the first argument is non-zero; otherwise it returns the value of its third argument.

The evaluation priorities are summarized below(2) (from stronger to weaker, i.e. * has a highest evaluation priority than +). Parentheses () may be used anywhere to change the order of evaluation:

1. (), [], ., #
2. ^
3. !, ++, --, - (unary)
4. *, /, %
5. +, -
6. <, >, <=, >=
7. ==, !=
8. &&
9. ||
10. ?:
11. =, +=, -=, *=, /=

2.3 Built-in functions

A built-in function is composed of an identifier followed by a pair of parentheses containing an expression-list (the list of its arguments)(3). Here is the list of the built-in functions currently implemented:

build-in-function:

Acos ( expression )

Arc cosine (inverse cosine) of an expression in [-1,1]. Returns a value in [0,Pi].

Asin ( expression )

Arc sine (inverse sine) of an expression in [-1,1]. Returns a value in [-Pi/2,Pi/2].

Atan ( expression )

Arc tangent (inverse tangent) of expression. Returns a value in [-Pi/2,Pi/2].

Atan2 ( expression, expression )

Arc tangent (inverse tangent) of the first expression divided by the second. Returns a value in [-Pi,Pi].

Ceil ( expression )

Rounds expression up to the nearest integer.

Cos ( expression )

Cosine of expression.

Cosh ( expression )

Hyperbolic cosine of expression.

Exp ( expression )

Returns the value of e (the base of natural logarithms) raised to the power of expression.

Fabs ( expression )

Absolute value of expression.

Fmod ( expression, expression )

Remainder of the division of the first expression by the second, with the sign of the first.

Floor ( expression )

Rounds expression down to the nearest integer.

Hypot ( expression, expression )

Returns the square root of the sum of the square of its two arguments.

Log ( expression )

Natural logarithm of expression (expression > 0).

Log10 ( expression )

Base 10 logarithm of expression (expression > 0).

Modulo ( expression, expression )

see Fmod( expression, expression ).

Rand ( expression )

Random number between zero and expression.

Sqrt ( expression )

Square root of expression (expression >= 0).

Sin ( expression )

Sine of expression.

Sinh ( expression )

Hyperbolic sine of expression.

Tan ( expression )

Tangent of expression.

Tanh ( expression )

Hyperbolic tangent of expression.

2.4 User-defined functions

User-defined functions take no arguments, and are evaluated as if a file containing the function body was included at the location of the Call statement.

Function string

Begins the declaration of a user-defined function named string. The body of the function starts on the line after `Function string', and can contain any Gmsh command.

Return

Ends the body of the current user-defined function. Function declarations cannot be imbricated.

Call string;

Executes the body of a (previously defined) function named string.

See 7.5 `t5.geo', for an example of a user-defined function.

2.5 Loops and conditionals

Loops and conditionals are defined as follows, and can be imbricated:

For ( expression : expression )

Iterates from the value of the first expression to the value of the second expression, with a unit incrementation step. At each iteration, the commands comprised between `For ( expression : expression )' and the matching EndFor are executed.

For ( expression : expression : expression )

Iterates from the value of the first expression to the value of the second expression, with a positive or negative incrementation step equal to the third expression. At each iteration, the commands comprised between `For ( expression : expression : expression )' and the matching EndFor are executed.

For string In { expression : expression }

Iterates from the value of the first expression to the value of the second expression, with a unit incrementation step. At each iteration, the value of the iterate is affected to an expression named string, and the commands comprised between `For string In { expression : expression }' and the matching EndFor are executed.

For string In { expression : expression : expression }

Iterates from the value of the first expression to the value of the second expression, with a positive or negative incrementation step equal to the third expression. At each iteration, the value of the iterate is affected to an expression named string, and the commands comprised between `For string In { expression : expression : expression }' and the matching EndFor are executed.

EndFor

Ends a matching For command.

If ( expression )

The body enclosed between `If ( expression )' and the matching Endif is evaluated if expression is non-zero.

EndIf

Ends a matching If command.

See 7.5 `t5.geo', for an example of For and If commands. Gmsh does not provide any Else (or similar) command at the time of this writing.

2.6 General commands

The following commands can be used anywhere in a Gmsh ASCII text input file:

string = expression;

Defines a new expression identifier string, or affects expression to an existing expression identifier. Eight expression identifiers are predefined (hardcoded in Gmsh's parser):

Pi

Returns 3.1415926535897932.

MPI_Size

Returns the number of processors on which Gmsh is running (always 1, except if you compiled Gmsh's parallel extensions).

MPI_Rank

Returns the rank of the current processor.

newp

Returns the next available point number. As we will see in 3. Geometry module, a unique number is associated with every geometrical point: newp permits to know the highest number already attributed. This is mostly useful when writing user-defined functions (see section 2.4 User-defined functions) or general geometric primitives, when one does not know a priori which numbers are already attributed, and which ones are still available.

newl

Returns the next available line number.

news

Returns the next available surface number.

newv

Returns the next available volume number.

newreg

Returns the next available region number. That is, newreg returns the maximum of newp, newl, news, newv and all physical entity numbers(4).

string [ ] = { expression-list };

Defines a new expression list identifier string[], or affects expression-list to an existing expression list identifier.

string [ { expression-list } ] = { expression-list };

Affects each item in the right hand side expression-list to the elements (indexed by the left hand side expression-list) of an existing expression list identifier. The two expression-lists must contain the same number of items. Remember the remark made when defining expression-lists: the braces enclosing an expression-list are optional if the list only contains a single item.

real-option = expression;

Affects expression to a real option.

char-option = char-expression;

Affects char-expression to a character option.

color-option = color-expression;

Affects color-expression to a color option.

string | real-option += expression;

Adds and affects expression to an existing expression identifier or to a real option.

string | real-option -= expression;

Subtracts and affects expression to an existing expression identifier or to a real option.

string | real-option *= expression;

Multiplies and affects expression to an existing expression identifier or to a real option.

string | real-option /= expression;

Divides and affects expression to an existing expression identifier or to a real option.

string [ { expression-list } ] += { expression-list };

Adds and affects, item per item, the right hand side expression-list to an existing expression list identifier.

string [ { expression-list } ] -= { expression-list };

Subtracts and affects, item per item, the right hand side expression-list to an existing expression list identifier.

string [ { expression-list } ] *= { expression-list };

Multiplies and affects, item per item, the right hand side expression-list to an existing expression list identifier.

string [ { expression-list } ] /= { expression-list };

Divides and affects, item per item, the right hand side expression-list to an existing expression list identifier.

Exit;

Aborts the current script.

Printf ( char-expression , expression-list );

Prints a character expression in the information window and/or on the terminal. Printf is equivalent to the printf C function: char-expression is a format string that can contain formatting characters (%f, %e, etc.). Note that all expressions are evaluated as floating point values in Gmsh (see section 2.1 Expressions), so that only valid floating point formatting characters make sense in char-expression. See 7.5 `t5.geo', for an example of the use of Printf.

Merge char-expression;

Merges a file named char-expression. This command is equivalent to the `File->Merge' menu in the graphical user interface.

Draw;

Redraws the scene. The bounding box of the scene is computed as follows:

1. If there is a geometry (i.e., at least one geometrical point), the bounding box is taken as the box enclosing all the geometrical points;
2. If there is no geometry but there is a mesh (i.e., at least one mesh vertex), the bounding box is taken as the box enclosing all the mesh vertices;
3. If there is no geometry and no mesh, but there are some post-processing views, the bounding box is taken as the box enclosing all the primitives of the last post-processing view.

Delete All;

Deletes all geometrical entities and all currently loaded meshes.

Print char-expression;

Prints the graphic window in a file named char-expression, using the current Print.Format (see section 2.7 General options).

Sleep expression;

Suspends the execution of Gmsh during expression seconds.

System char-expression;

Executes a system call.

Include char-expression;

Includes the file named char-expression at the current position in the input file. The include command should be given on a line of its own. If the path in char-expression is not absolute, char-expression is appended to the path of the including file.

2.7 General options

Here is the list of the general char-options, real-options and color-options (in that order--check the default values to see the actual types). Most of these options are accessible in the graphical user interface, but not all of them. When running Gmsh interactively, changing an option in the ASCII text input file will modify the option in the GUI in real time. This permits for example to resize the graphical window in a script, or to interact with animations in the script and in the GUI at the same time.

Gmsh's default behavior is to save some of these options in a per-user "session resource" file (General.SessionFileName) every time Gmsh is shut down. This permits for example to automatically remember the size and location of the windows or which fonts to use. Other options can be saved in a per-user "option" file (General.OptionsFileName), automatically loaded by Gmsh every time it starts up, by using the `Tools->Options->Save' menu.

General.DefaultFileName

Default project file name
Default value: "untitled.geo"
Saved in: General.SessionFileName

General.Display

X server to use (only for Unix versions)
Default value: ""
Saved in: -

General.ErrorFileName

File into which the log is saved if a fatal error occurs
Default value: ".gmsh-errors"
Saved in: General.SessionFileName

General.GraphicsFont

Font used in the graphic window
Default value: "Helvetica"
Saved in: General.SessionFileName

General.OptionsFileName

Option file created with `Tools->Options->Save'; automatically read on startup
Default value: ".gmsh-options"
Saved in: General.SessionFileName

General.SessionFileName

Option file into which session specific information is saved; automatically read on startup
Default value: ".gmshrc"
Saved in: -

General.Scheme

FLTK graphical user interface scheme (try e.g. plastic)
Default value: ""
Saved in: General.SessionFileName

General.TextEditor

System command to launch a text editor
Default value: "open -e %s"
Saved in: General.OptionsFileName

General.TmpFileName

Temporary file used by the geometry module
Default value: ".gmsh-tmp"
Saved in: General.SessionFileName

General.WebBrowser

System command to launch a web browser
Default value: "open %s"
Saved in: General.OptionsFileName

General.AlphaBlending

Enable alpha blending (transparency) in post-processing views
Default value: 1
Saved in: General.OptionsFileName

General.ArrowHeadRadius

Relative radius of arrow head
Default value: 0.12
Saved in: General.OptionsFileName

General.ArrowStemLength

Relative length of arrow stem
Default value: 0.56
Saved in: General.OptionsFileName

General.ArrowStemRadius

Relative radius of arrow stem
Default value: 0.02
Saved in: General.OptionsFileName

General.Axes

Display the axes linked to the model
Default value: 0
Saved in: General.OptionsFileName

General.Clip0

Enable clip plane 0
Default value: 0
Saved in: -

General.Clip0A

First coefficient in equation for clip plane 0 (`A' in `AX+BY+CZ+D=0')
Default value: 0
Saved in: -

General.Clip0B

Second coefficient in equation for clip plane 0 (`B' in `AX+BY+CZ+D=0')
Default value: 0
Saved in: -

General.Clip0C

Third coefficient in equation for clip plane 0 (`C' in `AX+BY+CZ+D=0')
Default value: 0
Saved in: -

General.Clip0D

Fourth coefficient in equation for clip plane 0 (`D' in `AX+BY+CZ+D=0')
Default value: 0
Saved in: -

General.Clip1

Enable clip plane 1
Default value: 0
Saved in: -

General.Clip1A

First coefficient in equation for clip plane 1
Default value: 0
Saved in: -

General.Clip1B

Second coefficient in equation for clip plane 1
Default value: 0
Saved in: -

General.Clip1C

Third coefficient in equation for clip plane 1
Default value: 0
Saved in: -

General.Clip1D

Fourth coefficient in equation for clip plane 1
Default value: 0
Saved in: -

General.Clip2

Enable clip plane 2
Default value: 0
Saved in: -

General.Clip2A

First coefficient in equation for clip plane 2
Default value: 0
Saved in: -

General.Clip2B

Second coefficient in equation for clip plane 2
Default value: 0
Saved in: -

General.Clip2C

Third coefficient in equation for clip plane 2
Default value: 0
Saved in: -

General.Clip2D

Fourth coefficient in equation for clip plane 2
Default value: 0
Saved in: -

General.Clip3

Enable clip plane 3
Default value: 0
Saved in: -

General.Clip3A

First coefficient in equation for clip plane 3
Default value: 0
Saved in: -

General.Clip3B

Second coefficient in equation for clip plane 3
Default value: 0
Saved in: -

General.Clip3C

Third coefficient in equation for clip plane 3
Default value: 0
Saved in: -

General.Clip3D

Fourth coefficient in equation for clip plane 3
Default value: 0
Saved in: -

General.Clip4

Enable clip plane 4
Default value: 0
Saved in: -

General.Clip4A

First coefficient in equation for clip plane 4
Default value: 0
Saved in: -

General.Clip4B

Second coefficient in equation for clip plane 4
Default value: 0
Saved in: -

General.Clip4C

Third coefficient in equation for clip plane 4
Default value: 0
Saved in: -

General.Clip4D

Fourth coefficient in equation for clip plane 4
Default value: 0
Saved in: -

General.Clip5

Enable clip plane 5
Default value: 0
Saved in: -

General.Clip5A

First coefficient in equation for clip plane 5
Default value: 0
Saved in: -

General.Clip5B

Second coefficient in equation for clip plane 5
Default value: 0
Saved in: -

General.Clip5C

Third coefficient in equation for clip plane 5
Default value: 0
Saved in: -

General.Clip5D

Fourth coefficient in equation for clip plane 5
Default value: 0
Saved in: -

General.ColorScheme

Default color scheme (0, 1 or 2)
Default value: 0
Saved in: General.OptionsFileName

General.ConfirmOverwrite

Ask confirmation before overwriting files?
Default value: 1
Saved in: General.SessionFileName

General.ContextPositionX

Horizontal position (in pixels) of the upper left corner of the contextual windows
Default value: 650
Saved in: General.SessionFileName

General.ContextPositionY

Vertical position (in pixels) of the upper left corner of the contextual windows
Default value: 150
Saved in: General.SessionFileName

General.DefaultPlugins

Load default plugins on startup
Default value: 1
Saved in: General.OptionsFileName

General.DoubleBuffer

Use a double buffered graphic window (on Unix, should be set to 0 when working on a remote host without GLX)
Default value: 1
Saved in: General.OptionsFileName

General.FastRedraw

Fast redraw (no mesh or view display) when interacting with the model
Default value: 1
Saved in: General.OptionsFileName

General.FontSize

Size of the font in the graphical user interface
Default value: 12
Saved in: General.SessionFileName

General.GraphicsFontSize

Size of the font in the graphic window
Default value: 14
Saved in: General.SessionFileName

General.GraphicsHeight

Height (in pixels) of the graphic window
Default value: 500
Saved in: General.SessionFileName

General.GraphicsPositionX

Horizontal position (in pixels) of the upper left corner of the graphic window
Default value: 20
Saved in: General.SessionFileName

General.GraphicsPositionY

Vertical position (in pixels) of the upper left corner of the graphic window
Default value: 30
Saved in: General.SessionFileName

General.GraphicsWidth

Width (in pixels) of the graphic window
Default value: 700
Saved in: General.SessionFileName

General.InitialModule

Module launched on startup (0=automatic, 1=geometry, 2=mesh, 3=solver, 4=post-processing)
Default value: 0
Saved in: General.OptionsFileName

General.Light0

Enable light source 0
Default value: 1
Saved in: General.OptionsFileName

General.Light0X

X position of light source 0
Default value: 0.5
Saved in: General.OptionsFileName

General.Light0Y

Y position of light source 0
Default value: 0.3
Saved in: General.OptionsFileName

General.Light0Z

Z position of light source 0
Default value: 1
Saved in: General.OptionsFileName

General.Light1

Enable light source 1
Default value: 0
Saved in: General.OptionsFileName

General.Light1X

X position of light source 1
Default value: 0.5
Saved in: General.OptionsFileName

General.Light1Y

Y position of light source 1
Default value: 0.3
Saved in: General.OptionsFileName

General.Light1Z

Z position of light source 1
Default value: 1
Saved in: General.OptionsFileName

General.Light2

Enable light source 2
Default value: 0
Saved in: General.OptionsFileName

General.Light2X

X position of light source 2
Default value: 0.5
Saved in: General.OptionsFileName

General.Light2Y

Y position of light source 2
Default value: 0.3
Saved in: General.OptionsFileName

General.Light2Z

Z position of light source 2
Default value: 1
Saved in: General.OptionsFileName

General.Light3

Enable light source 3
Default value: 0
Saved in: General.OptionsFileName

General.Light3X

X position of light source 3
Default value: 0.5
Saved in: General.OptionsFileName

General.Light3Y

Y position of light source 3
Default value: 0.3
Saved in: General.OptionsFileName

General.Light3Z

Z position of light source 3
Default value: 1
Saved in: General.OptionsFileName

General.Light4

Enable light source 4
Default value: 0
Saved in: General.OptionsFileName

General.Light4X

X position of light source 4
Default value: 0.5
Saved in: General.OptionsFileName

General.Light4Y

Y position of light source 4
Default value: 0.3
Saved in: General.OptionsFileName

General.Light4Z

Z position of light source 4
Default value: 1
Saved in: General.OptionsFileName

General.Light5

Enable light source 5
Default value: 0
Saved in: General.OptionsFileName

General.Light5X

X position of light source 5
Default value: 0.5
Saved in: General.OptionsFileName

General.Light5Y

Y position of light source 5
Default value: 0.3
Saved in: General.OptionsFileName

General.Light5Z

Z position of light source 5
Default value: 1
Saved in: General.OptionsFileName

General.LineWidth

Display width of lines (in pixels)
Default value: 1
Saved in: General.OptionsFileName

General.MenuPositionX

Horizontal position (in pixels) of the upper left corner of the menu window
Default value: 800
Saved in: General.SessionFileName

General.MenuPositionY

Vertical position (in pixels) of the upper left corner of the menu window
Default value: 50
Saved in: General.SessionFileName

General.MessagePositionX

Horizontal position (in pixels) of the upper left corner of the message window
Default value: 650
Saved in: General.SessionFileName

General.MessagePositionY

Vertical position (in pixels) of the upper left corner of the message window
Default value: 150
Saved in: General.SessionFileName

General.MessageHeight

Height (in pixels) of the message window
Default value: 350
Saved in: General.SessionFileName

General.MessageWidth

Width (in pixels) of the message window
Default value: 450
Saved in: General.SessionFileName

General.MovingLight

Use a moving (i.e. which follows the model) light source
Default value: 0
Saved in: General.OptionsFileName

General.OptionsPositionX

Horizontal position (in pixels) of the upper left corner of the option window
Default value: 650
Saved in: General.SessionFileName

General.OptionsPositionY

Vertical position (in pixels) of the upper left corner of the option window
Default value: 150
Saved in: General.SessionFileName

General.Orthographic

Orthographic projection mode (0=perspective projection)
Default value: 1
Saved in: General.OptionsFileName

General.PointSize

Display size of points (in pixels)
Default value: 3
Saved in: General.OptionsFileName

General.QuadricSubdivisions

Number of subdivisions used to draw points or lines as spheres or cylinders
Default value: 8
Saved in: General.OptionsFileName

General.RotationX

First Euler angle (used if Trackball=0)
Default value: 0
Saved in: -

General.RotationY

Second Euler angle (used if Trackball=0)
Default value: 0
Saved in: -

General.RotationZ

Third Euler angle (used if Trackball=0)
Default value: 0
Saved in: -

General.RotationCenterGravity

Rotate around the center of gravity instead of (RotationCenterX, RotationCenterY, RotationCenterZ)
Default value: 1
Saved in: General.OptionsFileName

General.RotationCenterX

X coordinate of the center of rotation
Default value: 0
Saved in: -

General.RotationCenterY

Y coordinate of the center of rotation
Default value: 0
Saved in: -

General.RotationCenterZ

Z coordinate of the center of rotation
Default value: 0
Saved in: -

General.SaveOptions

Automatically save current options in General.OptionsFileName each time you quit Gmsh?
Default value: 0
Saved in: General.SessionFileName

General.SaveSession

Automatically save session specific information in General.SessionFileName each time you quit Gmsh?
Default value: 1
Saved in: General.SessionFileName

General.ScaleX

X-axis scale factor
Default value: 1
Saved in: -

General.ScaleY

Y-axis scale factor
Default value: 1
Saved in: -

General.ScaleZ

Z-axis scale factor
Default value: 1
Saved in: -

General.Shininess

Material shininess (must be > 0)
Default value: 0.4
Saved in: General.OptionsFileName

General.SmallAxes

Display the small axes
Default value: 1
Saved in: General.OptionsFileName

General.SmallAxesPositionX

X position of small axes (use negative values for right alignment)
Default value: -60
Saved in: General.OptionsFileName

General.SmallAxesPositionY

Y position of small axes (use negative values for bottom alignment)
Default value: -40
Saved in: General.OptionsFileName

General.SolverPositionX

Horizontal position (in pixels) of the upper left corner of the solver windows
Default value: 650
Saved in: General.SessionFileName

General.SolverPositionY

Vertical position (in pixels) of the upper left corner of the solver windows
Default value: 150
Saved in: General.SessionFileName

General.StatisticsPositionX

Horizontal position (in pixels) of the upper left corner of the statistic window
Default value: 650
Saved in: General.SessionFileName

General.StatisticsPositionY

Vertical position (in pixels) of the upper left corner of the statistic window
Default value: 150
Saved in: General.SessionFileName

General.SystemMenuBar

Use the system menu bar on Mac OS X?
Default value: 1
Saved in: General.SessionFileName

General.Terminal

Should information be printed on the terminal (if available)?
Default value: 0
Saved in: General.OptionsFileName

General.Tooltips

Show tooltips in the graphical user interface
Default value: 1
Saved in: General.OptionsFileName

General.Trackball

Use trackball rotation mode
Default value: 1
Saved in: General.OptionsFileName

General.TrackballQuaternion0

First trackball quaternion component (used if General.Trackball=1)
Default value: 0
Saved in: -

General.TrackballQuaternion1

Second trackball quaternion component (used if General.Trackball=1)
Default value: 0
Saved in: -

General.TrackballQuaternion2

Third trackball quaternion component (used if General.Trackball=1)
Default value: 0
Saved in: -

General.TrackballQuaternion3

Fourth trackball quaternion component (used if General.Trackball=1)
Default value: 1
Saved in: -

General.TranslationX

X-axis translation (in model units)
Default value: 0
Saved in: -

General.TranslationY

Y-axis translation (in model units)
Default value: 0
Saved in: -

General.TranslationZ

Z-axis translation (in model units)
Default value: 0
Saved in: -

General.VectorType

Default vector display type (for normals, etc.)
Default value: 4
Saved in: General.OptionsFileName

General.Verbosity

Level of information printed during processing (0=no information)
Default value: 2
Saved in: General.OptionsFileName

General.VisibilityMode

Default mode for the visibility browser (0=Geometry+Mesh, 1=Geometry, 2=Mesh)
Default value: 0
Saved in: General.SessionFileName

General.VisibilityPositionX

Horizontal position (in pixels) of the upper left corner of the visibility window
Default value: 650
Saved in: General.SessionFileName

General.VisibilityPositionY

Vertical position (in pixels) of the upper left corner of the visibility window
Default value: 150
Saved in: General.SessionFileName

General.ZoomFactor

`Speed' of the middle mouse button zoom
Default value: 1.1
Saved in: General.OptionsFileName

General.Color.Background

Background color
Default value: {0,0,0}
Saved in: General.OptionsFileName

General.Color.Foreground

Foreground color
Default value: {255,255,255}
Saved in: General.OptionsFileName

General.Color.Text

Text color
Default value: {255,255,255}
Saved in: General.OptionsFileName

General.Color.Axes

Axes color
Default value: {255,255,0}
Saved in: General.OptionsFileName

General.Color.SmallAxes

Small axes color
Default value: {255,255,255}
Saved in: General.OptionsFileName

Print.EpsBackground

Save image background in PostScript/PDF output
Default value: 1
Saved in: General.OptionsFileName

Print.EpsBestRoot

Try to minimize primitive splitting in BSP tree sorted PostScript/PDF output
Default value: 1
Saved in: General.OptionsFileName

Print.EpsCompress

Compress PostScript/PDF output using zlib
Default value: 0
Saved in: General.OptionsFileName

Print.EpsLineWidthFactor

Width factor for lines in PostScript/PDF output
Default value: 0.5
Saved in: General.OptionsFileName

Print.EpsOcclusionCulling

Cull occluded primitives (to reduce PostScript/PDF file size)
Default value: 1
Saved in: General.OptionsFileName

Print.EpsPointSizeFactor

Size factor for points in PostScript/PDF output
Default value: 1
Saved in: General.OptionsFileName

Print.EpsPS3Shading

Enable PostScript Level 3 shading
Default value: 0
Saved in: General.OptionsFileName

Print.EpsQuality

PostScript/PDF quality (1=simple sort, 2=BSP tree sort)
Default value: 1
Saved in: General.OptionsFileName

Print.Format

File format (10=automatic)
Default value: 10
Saved in: General.OptionsFileName

Print.GifDither

Apply dithering to GIF output
Default value: 0
Saved in: General.OptionsFileName

Print.GifInterlace

Interlace GIF output
Default value: 0
Saved in: General.OptionsFileName

Print.GifSort

Sort the colormap in GIF output
Default value: 1
Saved in: General.OptionsFileName

Print.GifTransparent

Output transparent GIF image
Default value: 0
Saved in: General.OptionsFileName

Print.JpegQuality

JPEG quality (between 1 and 100)
Default value: 100
Saved in: General.OptionsFileName

3. Geometry module

Gmsh's geometry module provides a simple CAD engine, using a bottom-up approach: you need to first define points (using the Point command: see below), then lines (using Line, Circle, Spline, ..., commands or by extruding points), then surfaces (using for example the Plane Surface or Ruled Surface commands, or by extruding lines), and finally volumes (using the Volume command or by extruding surfaces).

These geometrical entities are called "elementary" in Gmsh's jargon, and are assigned identification numbers when they are created:

1. each elementary point must possess a unique identification number;
2. each elementary line must possess a unique identification number;
3. each elementary surface must possess a unique identification number;
4. each elementary volume must possess a unique identification number.

Elementary geometrical entities can then be manipulated in various ways, for example using the Translate, Rotate, Scale or Symmetry commands.

Compound groups of elementary geometrical entities can also be defined and are called "physical" entities. These physical entities cannot be modified by geometry commands: their only purpose is to assemble elementary entities into larger groups, possibly modifying their orientation, so that they can be referred to by the mesh module as single entities. As is the case with elementary entities, each physical point, physical line, physical surface or physical volume must be assigned a unique identification number. See 4. Mesh module, for more information about how physical entities affect the way meshes are saved.

3.1 Geometry commands
3.2 Geometry options

3.1 Geometry commands

The next subsections describe all the available geometry commands. These commands can be used anywhere in a Gmsh ASCII text input file. Note that the following general syntax rule is followed for the definition of geometrical entities: "If an expression defines a new entity, it is enclosed between parentheses. If an expression refers to a previously defined entity, it is enclosed between braces."

3.1.1 Points
3.1.2 Lines
3.1.3 Surfaces
3.1.4 Volumes
3.1.5 Extrusions
3.1.6 Transformations
3.1.7 Miscellaneous

3.1.1 Points

Point ( expression ) = { expression, expression, expression, expression };

Creates an elementary point. The expression inside the parentheses is the point's identification number; the three first expressions inside the braces on the right hand side give the three X, Y and Z coordinates of the point in the three-dimensional Euclidean space; the last expression sets the characteristic mesh length at that point. See 4.2.1 Characteristic lengths, for more information about how this characteristic length information is used in the meshing process.

Physical Point ( expression ) = { expression-list };

Creates a physical point. The expression inside the parentheses is the physical point's identification number; the expression-list on the right hand side should contain the identification numbers of all the elementary points that need to be grouped inside the physical point.

3.1.2 Lines

Bezier ( expression ) = { expression-list };

Creates a Bezier curve. The expression inside the parentheses is the Bezier curve's identification number; the expression-list on the right hand side should contain the identification numbers of all the curve's control points.

BSpline ( expression ) = { expression-list };

Creates a B-spline curve. The expression inside the parentheses is the B-spline curve's identification number; the expression-list on the right hand side should contain the identification numbers of all the B-spline's control points. Repeating control points has the expected effect.

Circle ( expression ) = { expression, expression, expression };

Creates a circle arc (strictly) smaller than Pi. The expression inside the parentheses is the circle arc's identification number; the first expression inside the braces on the right hand side gives the identification number of the start point of the arc; the second expression gives the identification number of the center of the circle; the last expression gives the identification number of the end point of the arc.

CatmullRom ( expression ) = { expression-list };

CatmullRom is a synonym for Spline.

Ellipse ( expression ) = { expression, expression, expression, expression };

Creates an ellipse arc. The expression inside the parentheses is the ellipse arc's identification number; the first expression inside the braces on the right hand side gives the identification number of the start point of the arc; the second expression gives the identification number of the center of the ellipse; the third expression gives the identification number of any point located on the major axis of the ellipse; the last expression gives the identification number of the end point of the arc. (A deprecated synonym for Ellipse is Ellipsis.)

Line ( expression ) = { expression, expression };

Creates a straight line segment. The expression inside the parentheses is the line segment's identification number; the two expressions inside the braces on the right hand side give identification numbers of the start and end points of the segment.

Spline ( expression ) = { expression-list };

Creates a spline curve. The expression inside the parentheses is the spline's identification number; the expression-list on the right hand side should contain the identification numbers of all the spline's control points.

Line Loop ( expression ) = { expression-list };

Creates an oriented line loop. The expression inside the parentheses is the line loop's identification number; the expression-list on the right hand side should contain the identification numbers of all the elementary lines that constitute the line loop. A line loop must be a closed loop, and the elementary lines should be ordered and oriented (using negative identification numbers to specify reverse orientation). If the orientation is correct, but the ordering is wrong, Gmsh will actually reorder the list internally to create a consistent loop. Although Gmsh supports it, it is not recommended to specify multiple line loops (or subloops) in a single Line Loop command. (Line loops are used to create surfaces: see 3.1.3 Surfaces.)

Physical Line ( expression ) = { expression-list };

Creates a physical line. The expression inside the parentheses is the physical line's identification number; the expression-list on the right hand side should contain the identification numbers of all the elementary lines that need to be grouped inside the physical line. Specifying negative identification numbers in the expression-list will reverse the orientation of the mesh elements belonging to the corresponding elementary lines in the saved mesh.

3.1.3 Surfaces

Plane Surface ( expression ) = { expression-list };

Creates a plane surface. The expression inside the parentheses is the plane surface's identification number; the expression-list on the right hand side should contain the identification numbers of all the line loops defining the surface. The first line loop defines the exterior boundary of the surface; all other line loops define holes in the surface.

Ruled Surface ( expression ) = { expression-list };

Creates a ruled surface, i.e. a surface that can be interpolated using transfinite interpolation. The expression inside the parentheses is the ruled surface's identification number; the expression-list on the right hand side should the identification number of a single line loop, composed of either three or four elementary lines.

Surface Loop ( expression ) = { expression-list };

Creates a surface loop (a shell). The expression inside the parentheses is the surface loop's identification number; the expression-list on the right hand side should contain the identification numbers of all the elementary surfaces that constitute the surface loop. A surface loop must always represent a closed shell, and the elementary surfaces should be oriented consistently (using negative identification numbers to specify reverse orientation). (Surface loops are used to create volumes: see 3.1.4 Volumes.)

Physical Surface ( expression ) = { expression-list };

Creates a physical surface. The expression inside the parentheses is the physical surface's identification number; the expression-list on the right hand side should contain the identification numbers of all the elementary surfaces that need to be grouped inside the physical surface. Specifying negative identification numbers in the expression-list will reverse the orientation of the mesh elements belonging to the corresponding elementary surfaces in the saved mesh.

3.1.4 Volumes

Volume ( expression ) = { expression-list };

Creates a volume. The expression inside the parentheses is the volume's identification number; the expression-list on the right hand side should contain the identification numbers of all the surface loops defining the volume. The first surface loop defines the exterior boundary of the volume; all other surface loops define holes in the volume. (A deprecated synonym for Volume is Complex Volume.)

Physical Volume ( expression ) = { expression-list };

Creates a physical volume. The expression inside the parentheses is the physical volume's identification number; the expression-list on the right hand side should contain the identification numbers of all the elementary volumes that need to be grouped inside the physical volume.

3.1.5 Extrusions

Lines, surfaces and volumes can also be created through extrusion of points, lines and surfaces, respectively. Here is the syntax of the geometrical extrusion commands (go to 4.2.2 Structured grids, to see how these commands can be extended in order to also extrude the mesh):

extrude:

Extrude Point | Line | Surface { expression, { expression-list } } ;

Extrudes the expression-th point, line or surface using a translation. The expression-list should contain three expressions giving the X, Y and Z components of the translation vector.

Extrude Point | Line | Surface { expression, { expression-list }, { expression-list }, expression };

Extrudes the expression-th point, line or surface using a rotation. The first expression-list should contain three expressions giving the X, Y and Z direction of the rotation axis; the second expression-list should contain three expressions giving the X, Y and Z components of any point on this axis; the last expression should contain the rotation angle (in radians).

Extrude Point | Line | Surface { expression, { expression-list }, { expression-list }, { expression-list }, expression };

Extrudes the expression-th point, line or surface using a translation combined with a rotation. The first expression-list should contain three expressions giving the X, Y and Z components of the translation vector; the second expression-list should contain three expressions giving the X, Y and Z direction of the rotation axis; the third expression-list should contain three expressions giving the X, Y and Z components of any point on this axis; the last expression should contain the rotation angle (in radians).

3.1.6 Transformations

Geometrical transformations can be applied to elementary entities, or to copies of geometrical entities (using the Duplicata command: see below). The syntax of the transformation commands is:

transform:

Dilate { { expression-list }, expression } { transform-list }

Scales all elementary entities (points, lines or surfaces) in transform-list by a factor expression. The expression-list should contain three expressions giving the X, Y and Z direction of the homothetic transformation.

Rotate { { expression-list }, { expression-list }, expression } { transform-list }

Rotates all elementary entities (points, lines or surfaces) in transform-list by an angle of expression radians. The first expression-list should contain three expressions giving the X, Y and Z direction of the rotation axis; the second expression-list should contain three expressions giving the X, Y and Z components of any point on this axis.

Symmetry { expression-list } { transform-list }

Transforms all elementary entities (points, lines or surfaces) symmetrically to a plane. The expression-list should contain four expressions giving the coefficients of the plane's equation.

Translate { expression-list } { transform-list }

Translates all elementary entities (points, lines or surfaces) in transform-list. The expression-list should contain three expressions giving the X, Y and Z components of the translation vector.

with

transform-list: Point | Line | Surface { expression-list }; ... | Duplicata { Point | Line | Surface { expression-list }; ... } | transform

3.1.7 Miscellaneous

Here is a list of all other geometry commands currently available:

Coherence;

Removes all duplicate elementary geometrical entities (e.g. points having identical coordinates). Note that Gmsh executes the Coherence command automatically after each geometrical transformation, unless Geometry.AutoCoherence is set to zero (see section 3.2 Geometry options).

Delete { Point | Line | Surface { expression-list }; ... }

Deletes all elementary entities (points, lines or surfaces) whose identification numbers are given in expression-list.

Hide { Point | Line | Surface | Volume { expression-list }; ... }

Hide the entities listed in expression-list, if General.VisibilityMode is set to 0 or 1.

Hide char-expression;

Hide the entity char-expression, if General.VisibilityMode is set to 0 or 1 (char-expression can for example be "*").

Show { Point | Line | Surface | Volume { expression-list }; ... }

Show the entities listed in expression-list, if General.VisibilityMode is set to 0 or 1.

Show char-expression;

Show the entity char-expression, if General.VisibilityMode is set to 0 or 1 (char-expression can for example be "*").

3.2 Geometry options

Geometry options control the behavior of geometry commands, as well as the way geometrical entities are handled in the graphical user interface. For the signification of the `Saved in:' field in the following list, see 2.7 General options.

Geometry.AutoCoherence

Should all duplicate entities be automatically removed?
Default value: 1
Saved in: General.OptionsFileName

Geometry.CirclePoints

Number of points used to draw a circle/ellipse
Default value: 20
Saved in: General.OptionsFileName

Geometry.ColorScheme

Default geometry color scheme (0, 1 or 2)
Default value: 0
Saved in: General.OptionsFileName

Geometry.CircleWarning

Warn if circle arc is greater than Pi
Default value: 1
Saved in: General.OptionsFileName

Geometry.ExtrudeSplinePoints

Number of control points for splines created during extrusion
Default value: 5
Saved in: General.OptionsFileName

Geometry.Highlight

Not used
Default value: 1
Saved in: General.OptionsFileName

Geometry.Light

Enable lighting for the geometry
Default value: 0
Saved in: General.OptionsFileName

Geometry.Lines

Display geometry curves?
Default value: 1
Saved in: General.OptionsFileName

Geometry.LineNumbers

Display curve numbers?
Default value: 0
Saved in: General.OptionsFileName

Geometry.LineSelectWidth

Display width of selected lines (in pixels)
Default value: 2
Saved in: General.OptionsFileName

Geometry.LineType

Display lines as solid color segments (0) or 3D cylinders (1)
Default value: 0
Saved in: General.OptionsFileName

Geometry.LineWidth

Display width of lines (in pixels)
Default value: 2
Saved in: General.OptionsFileName

Geometry.Normals

Display size of normal vectors (in pixels)
Default value: 0
Saved in: General.OptionsFileName

Geometry.OldCircle

Use old circle description (compatibility option for old Gmsh geometries)
Default value: 0
Saved in: General.OptionsFileName

Geometry.OldNewReg

Use old newreg definition for geometrical transformations (compatibility option for old Gmsh geometries)
Default value: 1
Saved in: General.OptionsFileName

Geometry.Points

Display geometry points?
Default value: 1
Saved in: General.OptionsFileName

Geometry.PointNumbers

Display points numbers?
Default value: 0
Saved in: General.OptionsFileName

Geometry.PointSelectSize

Display size of selected points (in pixels)
Default value: 5
Saved in: General.OptionsFileName

Geometry.PointSize

Display size of points (in pixels)
Default value: 4
Saved in: General.OptionsFileName

Geometry.PointType

Display points as solid color dots (0) or 3D spheres (1)
Default value: 0
Saved in: General.OptionsFileName

Geometry.ScalingFactor

Global geometry scaling factor
Default value: 1
Saved in: General.OptionsFileName

Geometry.StlCreateElementary

Treat each STL input face as a new geometrical surface
Default value: 1
Saved in: General.OptionsFileName

Geometry.StlCreatePhysical

Automatically create physical entities when importing STL faces as geometrical surfaces
Default value: 1
Saved in: General.OptionsFileName

Geometry.Surfaces

Display geometry surfaces?
Default value: 0
Saved in: General.OptionsFileName

Geometry.SurfaceNumbers

Display surface numbers?
Default value: 0
Saved in: General.OptionsFileName

Geometry.Tangents

Display size of tangent vectors (in pixels)
Default value: 0
Saved in: General.OptionsFileName

Geometry.Volumes

Display geometry volumes? (not implemented yet)
Default value: 0
Saved in: General.OptionsFileName

Geometry.VolumeNumbers

Display volume numbers? (not implemented yet)
Default value: 0
Saved in: General.OptionsFileName

Geometry.Color.Points

Normal geometry point color
Default value: {178,182,129}
Saved in: General.OptionsFileName

Geometry.Color.Lines

Normal geometry curve color
Default value: {0,0,255}
Saved in: General.OptionsFileName

Geometry.Color.Surfaces

Normal geometry surface color
Default value: {128,128,128}
Saved in: General.OptionsFileName

Geometry.Color.Volumes

Normal geometry volume color
Default value: {128,128,128}
Saved in: General.OptionsFileName

Geometry.Color.PointsSelect

Selected geometry point color
Default value: {255,0,0}
Saved in: General.OptionsFileName

Geometry.Color.LinesSelect

Selected geometry curve color
Default value: {255,0,0}
Saved in: General.OptionsFileName

Geometry.Color.SurfacesSelect

Selected geometry surface color
Default value: {255,0,0}
Saved in: General.OptionsFileName

Geometry.Color.VolumesSelect

Selected geometry volume color
Default value: {255,0,0}
Saved in: General.OptionsFileName

Geometry.Color.PointsHighlight

Highlighted geometry point color
Default value: {0,255,0}
Saved in: General.OptionsFileName

Geometry.Color.LinesHighlight

Highlighted geometry curve color
Default value: {0,0,255}
Saved in: General.OptionsFileName

Geometry.Color.SurfacesHighlight

Highlighted geometry surface color
Default value: {128,128,128}
Saved in: General.OptionsFileName

Geometry.Color.VolumesHighlight

Highlighted geometry volume color
Default value: {128,128,128}
Saved in: General.OptionsFileName

Geometry.Color.Tangents

Tangent geometry vectors color
Default value: {255,255,0}
Saved in: General.OptionsFileName

Geometry.Color.Normals

Normal geometry vectors color
Default value: {255,0,0}
Saved in: General.OptionsFileName

4. Mesh module

Gmsh's mesh module regroups several 1D, 2D and 3D mesh algorithms, all producing grids conforming in the sense of finite elements (see section 1.2 Mesh: finite element mesh generation).

The 2D unstructured algorithms generate triangles or both triangles and quadrangles (when Recombine Surface is used: see 4.2.3 Miscellaneous). The 3D unstructured algorithm only generates tetrahedra.

The 2D structured algorithms (transfinite and extrusion) generate triangles by default, but quadrangles can be obtained by using the Recombine commands (see 4.2.2 Structured grids, and 4.2.3 Miscellaneous). The 3D structured algorithms generate tetrahedra, hexahedra, prisms and pyramids, depending on the type of the surface meshes they are based on.

4.1 Elementary vs. physical entities
4.2 Mesh commands
4.3 Mesh options

4.1 Elementary vs. physical entities

If only elementary geometrical entities are defined (or if the Mesh.SaveAll option is set; see 4.3 Mesh options), the grid produced by the mesh module will be saved "as is". That is, all the elements in the grid will be saved to disk using the identification number of the elementary entities they discretize as their region number (see section 9.1 Gmsh mesh file format). This can sometimes be inconvenient:

• mesh elements cannot be duplicated;
• the orientation of the mesh elements (the ordering of their nodes) is determined entirely by the orientation of their "parent" elementary entities, and cannot be modified;
• elements belonging to different elementary entities cannot be linked as being part of a larger group having a physical or mathematical meaning (like `Left wing', `Metallic part', `Dirichlet boundary condition', ...).

To remedy these problems, the geometry module introduces the notion of "physical" entities (see section 3. Geometry module). The purpose of physical entities is to assemble elementary entities into larger, possibly overlapping groups, and to control the orientation of the elements in these groups. If physical entities are defined, the output mesh only contains those elements that belong to physical entities. The introduction of such physical entities in large models usually greatly facilitates the manipulation of the model (e.g. using `Tools->Visibility' in the GUI) and the interfacing with external solvers.

4.2 Mesh commands

The mesh module commands mostly permit to modify the characteristic lengths and specify structured grid parameters. The actual mesh "actions" (i.e., "mesh the lines", "mesh the surfaces" and "mesh the volumes") cannot be specified in the input ASCII text input files. They have to be given either in the GUI or on the command line (see 8. Running Gmsh, and 8.2 Command-line options).

4.2.1 Characteristic lengths
4.2.2 Structured grids
4.2.3 Miscellaneous

4.2.1 Characteristic lengths

The `size' of a mesh element is defined as the length of the segment for a line segment, the radius of the circumscribed circle for a triangle and the radius of the circumscribed sphere for a tetrahedron. There are three main ways to specify the size of the mesh elements for a given geometry:

1. You can specify characteristic lengths at the points of the geometrical model (with the Point command: see 3.1.1 Points). The actual size of the mesh elements will be computed by linearly interpolating these characteristic lengths on the initial mesh (see 1.2 Mesh: finite element mesh generation). This might sometimes lead to over-refinement in some areas, so that you may have to add "dummy" geometrical entities in the model in order to get the desired element sizes.

   This method works with all the algorithms implemented in the mesh module. The final element sizes are of course constrained by the structured algorithms for which the element sizes are explicitly specified (e.g. transfinite and extruded grids: see 4.2.2 Structured grids).

2. You can use geometrical "attractors", an elaborate version of the method described in the preceding item: see the definition of the Attractor command below.

   Note that attractors currently only work with the 2D anisotropic algorithm (see the Mesh.Algorithm option in 4.3 Mesh options).

3. You can give Gmsh an explicit background mesh in the form of a scalar post-processing view (see 6.1 Post-processing commands, and 9. File formats) in which the nodal values are the target element sizes. This method is very general but it requires a first (usually rough) mesh and a way to compute the target sizes on this mesh (usually through an error estimation procedure, in an iterative process of mesh adaptation). Note that the target element sizes can be constrained by the characteristic lengths defined in the geometrical model if the Mesh.ConstrainedBackgroundMesh option is set.

   This method only works with the isotropic 1D, 2D and 3D algorithm, and is not currently available with the Triangle algorithm. To load a background mesh, use the -bgm command-line option (see section 8.2 Command-line options) or select `Apply as background mesh' in the post-processing view option menu.

Here are the mesh commands that are related to the specification of characteristic lengths:

Attractor Point | Line { expression-list } = { expression, expression, expression };

Specifies a characteristic length attractor. The expression-list should contain the identification numbers of the elementary points or lines to serve as attractors; the two first expressions prescribe refinement factors in a coordinate system local to the entities, and the last expression a decay factor. This feature is still experimental, and only works with the 2D anisotropic algorithm (see Mesh.Algorithm in 4.3 Mesh options). An example of the use of attractors is given in 7.7 `t7.geo'.

Characteristic Length { expression-list } = expression;

Modifies the characteristic length of the points whose identification numbers are listed in expression-list. The new value is given by expression.

4.2.2 Structured grids

Extrude Point | Line | Surface { expression, { expression-list } } { layers; ... } ;

Extrudes both the geometry and the mesh using a translation (see section 3.1.5 Extrusions). The layers option determines how the mesh is extruded and has the following syntax:

layers: Layer { { expression-list }, { expression-list }, { expression-list } }; | Recombine;

The first expression-list defines how many elements should be created in each extruded layer. The second expression-list assigns a region number to each layer. The last expression-list gives the normalized height of each layer (the list should contain a sequence of n numbers 0 < h1 < h2 < ... < hn <= 1). See 7.3 `t3.geo', for an example.

For line extrusions, the Recombine option will recombine triangles into quadrangles when possible. For surface extrusions, the Recombine option will recombine tetrahedra into prisms, hexahedra or pyramids.

Extrude Point | Line | Surface { expression, { expression-list }, { expression-list }, expression } { layers; ... };

Extrudes both the geometry and the mesh using a rotation (see section 3.1.5 Extrusions). The layers option is defined as above.

Extrude Point | Line | Surface { expression, { expression-list }, { expression-list }, { expression-list }, expression } { layers; ... };

Extrudes both the geometry and the mesh using a combined translation and rotation (see section 3.1.5 Extrusions). The layers option is defined as above.

Transfinite Line { expression-list } = expression < Using Progression | Bump expression >

Selects the lines in expression-list to be meshed with the 1D transfinite algorithm. The expression on the right hand side gives the number of nodes that will be created on the line (this overrides any characteristic length prescription--see 4.2.1 Characteristic lengths). The optional argument `Using Progression expression' instructs the transfinite algorithm to distribute the nodes following a geometric progression (Progression 2 meaning for example that each line element in the series will be twice as long as the preceding one). The optional argument `Using Bump expression' instructs the transfinite algorithm to distribute the nodes with a refinement at both ends of the line. (A deprecated synonym for Progression is Power.)

Transfinite Surface { expression } = { expression-list };

Selects the surface expression to be meshed with the 2D transfinite algorithm (the surface can only have three or four sides). The expression-list should contain the identification numbers of the points on the boundary of the surface. The ordering of these point numbers defines the ordering and orientation of the mesh elements, and should thus follow the node ordering for triangles or quadrangles given in 9.5 Gmsh node ordering.

Transfinite Volume { expression } = { expression-list };

Selects the volume expression to be meshed with the 3D transfinite algorithm (the volume can only have six or eight faces). The expression-list should contain the identification numbers of the points on the boundary of the volume. The ordering of these point numbers defines the ordering and orientation of the mesh elements, and should thus follow the node ordering for prisms or hexahedra given in 9.5 Gmsh node ordering.

4.2.3 Miscellaneous

Here is a list of all other mesh commands currently available:

Color color-expression { Point | Line | Surface | Volume { expression-list }; ... }

Sets the mesh color of the entities in expression-list to color-expression.

Hide { Point | Line | Surface | Volume { expression-list }; ... }

Hides the mesh of the entities in expression-list, if General.VisibilityMode is set to 0 or 2.

Hide char-expression;

Hides the mesh of the entity char-expression, if General.VisibilityMode is set to 0 or 2 (char-expression can for example be "*").

Recombine Surface { expression-list } < = expression >;

Recombines the triangular meshes of the surfaces listed in expression-list into mixed triangular/quadrangular meshes. The optional expression on the right hand side specifies the maximum recombination angle allowed (a large expression leading to more triangle recombinations).

Save char-expression;

Saves the mesh in a file named char-expression, using the current Mesh.Format (see section 4.3 Mesh options).

Show { Point | Line | Surface | Volume { expression-list }; ... }

Shows the mesh of the entities in expression-list, if General.VisibilityMode is set to 0 or 2.

Show char-expression;

Shows the mesh of the entity char-expression, if General.VisibilityMode is set to 0 or 2 (char-expression can for example be "*").

4.3 Mesh options

Mesh options control the behavior of mesh commands, as well as the way meshes are displayed in the graphical user interface. For the signification of the `Saved in:' field in the following list, see 2.7 General options.

Mesh.TriangleOptions

Options for Jonathan Shewchuk's Triangle isotropic algorithm
Default value: "praqzBPY"
Saved in: General.OptionsFileName

Mesh.Algorithm

2D mesh algorithm (1=isotropic, 2=anisotropic, 3=triangle)
Default value: 1
Saved in: General.OptionsFileName

Mesh.AllowDegeneratedExtrude

Allow the generation of degenerated hexahedra or prisms during extrusion
Default value: 0
Saved in: -

Mesh.CharacteristicLengthFactor

Factor applied to all characteristic lengths (and background meshes)
Default value: 1
Saved in: General.OptionsFileName

Mesh.ColorCarousel

Color mesh by region? (0=no, 1=by elementary entity, 2=by physical entity, 3=by partition)
Default value: 1
Saved in: General.OptionsFileName

Mesh.ColorScheme

Default mesh color scheme (0, 1 or 2)
Default value: 0
Saved in: General.OptionsFileName

Mesh.ConstrainedBackgroundMesh

Should the background mesh be constrained by the characteristic lengths associated with the geometry?
Default value: 0
Saved in: General.OptionsFileName

Mesh.CpuTime

CPU time for the generation of the current mesh (in seconds)
Default value: 0
Saved in: -

Mesh.CutPlane

Enable mesh cut plane
Default value: 0
Saved in: -

Mesh.CutPlaneAsSurface

Draw the intersection volume layer as a surface
Default value: 0
Saved in: -

Mesh.CutPlaneA

First cut plane equation coefficient (`A' in `AX+BY+CZ+D=0')
Default value: 1
Saved in: -

Mesh.CutPlaneB

Second cut plane equation coefficient (`B' in `AX+BY+CZ+D=0')
Default value: 0
Saved in: -

Mesh.CutPlaneC

Third cut plane equation coefficient (`C' in `AX+BY+CZ+D=0')
Default value: 0
Saved in: -

Mesh.CutPlaneD

Fourth cut plane equation coefficient (`D' in `AX+BY+CZ+D=0')
Default value: 0
Saved in: -

Mesh.DisplayLists

Use OpenGL display lists for drawing meshes
Default value: 0
Saved in: General.OptionsFileName

Mesh.Dual

Display the dual mesh obtained by barycentric subdivision
Default value: 0
Saved in: General.OptionsFileName

Mesh.ElementOrder

Element order (1=linear elements, 2=quadratic elements)
Default value: 1
Saved in: General.OptionsFileName

Mesh.Explode

Display mesh with non adjacent elements (factor between 0 and 1)
Default value: 1
Saved in: General.OptionsFileName

Mesh.Format

Mesh output format (1=MSH, 2=UNV, 3=GREF, 19=VRML)
Default value: 1
Saved in: General.OptionsFileName

Mesh.GammaInf

Only display elements whose Gamma factor is greater than GammaInf
Default value: 0
Saved in: General.OptionsFileName

Mesh.GammaSup

Only display elements whose Gamma factor is smaller than GammaSup
Default value: 0
Saved in: General.OptionsFileName

Mesh.Interactive

Show the construction of the 2D mesh in real time (only with the 2D anisotropic algorithm)
Default value: 0
Saved in: General.OptionsFileName

Mesh.Light

Enable lighting for the mesh
Default value: 0
Saved in: General.OptionsFileName

Mesh.Lines

Display mesh lines (1D elements)?
Default value: 0
Saved in: General.OptionsFileName

Mesh.LineNumbers

Display mesh line numbers?
Default value: 0
Saved in: General.OptionsFileName

Mesh.LineType

Display mesh lines as solid color segments (0) or 3D cylinders (1)
Default value: 0
Saved in: General.OptionsFileName

Mesh.LineWidth

Display width of mesh lines (in pixels)
Default value: 1
Saved in: General.OptionsFileName

Mesh.MinimumCirclePoints

Minimum number of points used to mesh a circle
Default value: 7
Saved in: General.OptionsFileName

Mesh.MshFileVersion

MSH mesh file version to generate
Default value: 1
Saved in: General.OptionsFileName

Mesh.NbHexahedra

Number of hexahedra in the current mesh
Default value: 0
Saved in: -

Mesh.NbNodes

Number of nodes in the current mesh
Default value: 0
Saved in: -

Mesh.NbPrisms

Number of prisms in the current mesh
Default value: 0
Saved in: -

Mesh.NbPyramids

Number of pyramids in the current mesh
Default value: 0
Saved in: -

Mesh.NbQuadrangles

Number of quadrangles in the current mesh
Default value: 0
Saved in: -

Mesh.NbTetrahedra

Number of tetrahedra in the current mesh
Default value: 0
Saved in: -

Mesh.NbTriangles

Number of triangles in the current mesh
Default value: 0
Saved in: -

Mesh.Normals

Display size of normal vectors (in pixels)
Default value: 0
Saved in: General.OptionsFileName

Mesh.Points

Display mesh vertices (nodes)?
Default value: 1
Saved in: General.OptionsFileName

Mesh.PointInsertion

Point insertion method for isotropic 2D algorithm (1=center of circumscribed circle, 2=cog)
Default value: 1
Saved in: General.OptionsFileName

Mesh.PointNumbers

Display mesh node numbers?
Default value: 0
Saved in: General.OptionsFileName

Mesh.PointSize

Display size of mesh vertices (in pixels)
Default value: 3
Saved in: General.OptionsFileName

Mesh.PointType

Display mesh vertices as solid color dots (0) or 3D spheres (1)
Default value: 0
Saved in: General.OptionsFileName

Mesh.Quality

Target quality for tetrahedral elements (not fully functional)
Default value: 0
Saved in: General.OptionsFileName

Mesh.RadiusInf

Only display elements whose Radius is greater than RadiusInf
Default value: 0
Saved in: General.OptionsFileName

Mesh.RadiusSup

Only display elements whose Radius is smaller than RadiusSup
Default value: 0
Saved in: General.OptionsFileName

Mesh.RandomFactor

Random factor used in 2D and 3D meshing algorithm (test other values when the algorithm fails)
Default value: 0.0001
Saved in: General.OptionsFileName

Mesh.SaveAll

Ignore Physical definitions and save all elements
Default value: 0
Saved in: -

Mesh.ScalingFactor

Global scaling factor applied to the saved mesh
Default value: 1
Saved in: General.OptionsFileName

Mesh.Smoothing

Number of smoothing steps applied to the final mesh
Default value: 0
Saved in: General.OptionsFileName

Mesh.SpeedMax

Disable dubious point insertion tests
Default value: 0
Saved in: General.OptionsFileName

Mesh.SurfaceEdges

Display edges of surface mesh?
Default value: 1
Saved in: General.OptionsFileName

Mesh.SurfaceFaces

Display faces of surface mesh?
Default value: 0
Saved in: General.OptionsFileName

Mesh.SurfaceNumbers

Display surface mesh element numbers?
Default value: 0
Saved in: General.OptionsFileName

Mesh.Tangents

Display size of tangent vectors (in pixels)
Default value: 0
Saved in: General.OptionsFileName

Mesh.VolumeEdges

Display edges of volume mesh?
Default value: 1
Saved in: General.OptionsFileName

Mesh.VolumeFaces

Display faces of volume mesh?
Default value: 0
Saved in: General.OptionsFileName

Mesh.VolumeNumbers

Display volume mesh element numbers?
Default value: 0
Saved in: General.OptionsFileName

Mesh.Color.Points

Mesh node color
Default value: {0,255,0}
Saved in: General.OptionsFileName

Mesh.Color.PointsSup

Second order mesh node color
Default value: {255,0,255}
Saved in: General.OptionsFileName

Mesh.Color.Lines

Mesh line color
Default value: {0,255,0}
Saved in: General.OptionsFileName

Mesh.Color.Triangles

Mesh triangle color (if Mesh.ColorCarousel=0)
Default value: {160,150,255}
Saved in: General.OptionsFileName

Mesh.Color.Quadrangles

Mesh quadrangle color (if Mesh.ColorCarousel=0)
Default value: {130,120,225}
Saved in: General.OptionsFileName

Mesh.Color.Tetrahedra

Mesh tetrahedron color (if Mesh.ColorCarousel=0)
Default value: {160,150,255}
Saved in: General.OptionsFileName

Mesh.Color.Hexahedra

Mesh hexahedron color (if Mesh.ColorCarousel=0)
Default value: {130,120,225}
Saved in: General.OptionsFileName

Mesh.Color.Prisms

Mesh prism color (if Mesh.ColorCarousel=0)
Default value: {232,210,23}
Saved in: General.OptionsFileName

Mesh.Color.Pyramids

Mesh pyramid color (if Mesh.ColorCarousel=0)
Default value: {217,113,38}
Saved in: General.OptionsFileName

Mesh.Color.Tangents

Tangent mesh vector color
Default value: {255,255,0}
Saved in: General.OptionsFileName

Mesh.Color.Normals

Normal mesh vector color
Default value: {255,0,0}
Saved in: General.OptionsFileName

Mesh.Color.One

First color in color carousel
Default value: {232,210,23}
Saved in: General.OptionsFileName

Mesh.Color.Two

Second color in color carousel
Default value: {226,167,29}
Saved in: General.OptionsFileName

Mesh.Color.Three

Third color in color carousel
Default value: {217,113,38}
Saved in: General.OptionsFileName

Mesh.Color.Four

Fourth color in color carousel
Default value: {201,54,54}
Saved in: General.OptionsFileName

Mesh.Color.Five

Fifth color in color carousel
Default value: {169,12,86}
Saved in: General.OptionsFileName

Mesh.Color.Six

Sixth color in color carousel
Default value: {114,2,141}
Saved in: General.OptionsFileName

Mesh.Color.Seven

Seventh color in color carousel
Default value: {67,30,188}
Saved in: General.OptionsFileName

Mesh.Color.Eight

Eighth color in color carousel
Default value: {44,86,211}
Saved in: General.OptionsFileName

Mesh.Color.Nine

Ninth color in color carousel
Default value: {32,145,223}
Saved in: General.OptionsFileName

Mesh.Color.Ten

Tenth color in color carousel
Default value: {25,193,230}
Saved in: General.OptionsFileName

5. Solver module

Five external solvers can be interfaced simultaneously with Gmsh.

If you just want to start a solver from the solver module, with no further interactions between the solver and Gmsh, just edit the options relative to one of the five available solvers (e.g. Solver.Name0, Solver.Executable0, ...; see 5.1 Solver options), and set the corresponding "client-server" option to zero (e.g. Solver.ClientServer0 = 0). This doesn't require any modification to be made to the solver.

If you want the solver to interact with Gmsh (for error messages, option definitions, post-processing, etc.), you need to link your solver with the `GmshClient.c' file and add the appropriate function calls inside your program. You can then proceed as in the previous case, but this time you should set the client-server option to 1 (e.g. Solver.ClientServer0 = 1), so that Gmsh and the solver can communicate through a Unix socket. See 5.2 Solver example, for an example of how to interface a C solver. Bindings for solvers written in other languages (e.g. Perl) are available on http://www.geuz.org/gmsh/.

5.1 Solver options
5.2 Solver example

5.1 Solver options

Solver.Name0

Name of solver 0
Default value: "GetDP"
Saved in: General.OptionsFileName

Solver.Help0

Help string for solver 0
Default value: "A General environment for the treatment of Discrete Problems. Copyright (C) 1997-2004 Patrick Dular and Christophe Geuzaine. Visit http://www.geuz.org/getdp/ for more info"
Saved in: General.OptionsFileName

Solver.Executable0

System command to launch solver 0 (should not contain the `&' character)
Default value: "getdp"
Saved in: General.OptionsFileName

Solver.Extension0

Default file name extension for solver 0
Default value: ".pro"
Saved in: General.OptionsFileName

Solver.MeshName0

Default mesh file name for solver 0
Default value: ""
Saved in: General.OptionsFileName

Solver.MeshCommand0

Command used to specify the mesh file for solver 0
Default value: "-msh %s"
Saved in: General.OptionsFileName

Solver.OptionCommand0

Command to get options from solver 0
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstOption0

Label of first option for solver 0
Default value: "Resolution"
Saved in: General.OptionsFileName

Solver.SecondOption0

Label of second option for solver 0
Default value: "PostOperation"
Saved in: General.OptionsFileName

Solver.ThirdOption0

Label of third option for solver 0
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthOption0

Label of fourth option for solver 0
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthOption0

Label of fifth option for solver 0
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstButton0

Label of first button for solver 0
Default value: "Pre"
Saved in: General.OptionsFileName

Solver.FirstButtonCommand0

Command associated with the first button for solver 0
Default value: "-pre %s"
Saved in: General.OptionsFileName

Solver.SecondButton0

Label of second button for solver 0
Default value: "Cal"
Saved in: General.OptionsFileName

Solver.SecondButtonCommand0

Command associated with the second button for solver 0
Default value: "-cal"
Saved in: General.OptionsFileName

Solver.ThirdButton0

Label of third button for solver 0
Default value: "Pos"
Saved in: General.OptionsFileName

Solver.ThirdButtonCommand0

Command associated with the third button for solver 0
Default value: "-bin -pos %s"
Saved in: General.OptionsFileName

Solver.FourthButton0

Label of fourth button for solver 0
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthButtonCommand0

Command associated with the fourth button for solver 0
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthButton0

Label of fifth button for solver 0
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthButtonCommand0

Command associated with the fifth button for solver 0
Default value: ""
Saved in: General.OptionsFileName

Solver.Name1

Name of solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.Help1

Help string for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.Executable1

System command to launch solver 1 (should not contain the `&' character)
Default value: ""
Saved in: General.OptionsFileName

Solver.Extension1

Default file name extension for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.MeshName1

Default mesh file name for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.MeshCommand1

Command used to specify the mesh file for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.OptionCommand1

Command to get options from solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstOption1

Label of first option for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondOption1

Label of second option for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdOption1

Label of third option for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthOption1

Label of fourth option for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthOption1

Label of fifth option for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstButton1

Label of first button for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstButtonCommand1

Command associated with the first button for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondButton1

Label of second button for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondButtonCommand1

Command associated with the second button for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdButton1

Label of third button for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdButtonCommand1

Command associated with the third button for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthButton1

Label of fourth button for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthButtonCommand1

Command associated with the fourth button for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthButton1

Label of fifth button for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthButtonCommand1

Command associated with the fifth button for solver 1
Default value: ""
Saved in: General.OptionsFileName

Solver.Name2

Name of solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.Help2

Help string for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.Executable2

System command to launch solver 2 (should not contain the `&' character)
Default value: ""
Saved in: General.OptionsFileName

Solver.Extension2

Default file name extension for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.MeshName2

Default mesh file name for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.MeshCommand2

Command used to specify the mesh file for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.OptionCommand2

Command to get options from solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstOption2

Label of first option for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondOption2

Label of second option for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdOption2

Label of third option for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthOption2

Label of fourth option for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthOption2

Label of fifth option for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstButton2

Label of first button for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstButtonCommand2

Command associated with the first button for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondButton2

Label of second button for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondButtonCommand2

Command associated with the second button for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdButton2

Label of third button for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdButtonCommand2

Command associated with the third button for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthButton2

Label of fourth button for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthButtonCommand2

Command associated with the fourth button for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthButton2

Label of fifth button for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthButtonCommand2

Command associated with the fifth button for solver 2
Default value: ""
Saved in: General.OptionsFileName

Solver.Name3

Name of solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.Help3

Help string for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.Executable3

System command to launch solver 3 (should not contain the `&' character)
Default value: ""
Saved in: General.OptionsFileName

Solver.Extension3

Default file name extension for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.MeshName3

Default mesh file name for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.MeshCommand3

Command used to specify the mesh file for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.OptionCommand3

Command to get options from solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstOption3

Label of first option for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondOption3

Label of second option for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdOption3

Label of third option for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthOption3

Label of fourth option for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthOption3

Label of fifth option for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstButton3

Label of first button for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstButtonCommand3

Command associated with the first button for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondButton3

Label of second button for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondButtonCommand3

Command associated with the second button for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdButton3

Label of third button for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdButtonCommand3

Command associated with the third button for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthButton3

Label of fourth button for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthButtonCommand3

Command associated with the fourth button for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthButton3

Label of fifth button for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthButtonCommand3

Command associated with the fifth button for solver 3
Default value: ""
Saved in: General.OptionsFileName

Solver.Name4

Name of solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.Help4

Help string for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.Executable4

System command to launch solver 4 (should not contain the `&' character)
Default value: ""
Saved in: General.OptionsFileName

Solver.Extension4

Default file name extension for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.MeshName4

Default mesh file name for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.MeshCommand4

Command used to specify the mesh file for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.OptionCommand4

Command to get options from solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstOption4

Label of first option for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondOption4

Label of second option for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdOption4

Label of third option for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthOption4

Label of fourth option for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthOption4

Label of fifth option for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstButton4

Label of first button for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.FirstButtonCommand4

Command associated with the first button for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondButton4

Label of second button for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.SecondButtonCommand4

Command associated with the second button for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdButton4

Label of third button for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.ThirdButtonCommand4

Command associated with the third button for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthButton4

Label of fourth button for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.FourthButtonCommand4

Command associated with the fourth button for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthButton4

Label of fifth button for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.FifthButtonCommand4

Command associated with the fifth button for solver 4
Default value: ""
Saved in: General.OptionsFileName

Solver.ClientServer0

Connect solver 0 to the Gmsh server
Default value: 1
Saved in: General.OptionsFileName

Solver.MergeViews0

Automatically merge any post-processing view created by solver 0
Default value: 1
Saved in: General.OptionsFileName

Solver.PopupMessages0

Automatically display messages produced by solver 0
Default value: 1
Saved in: General.OptionsFileName

Solver.ClientServer1

Connect solver 1 to the Gmsh server
Default value: 0
Saved in: General.OptionsFileName

Solver.MergeViews1

Automatically merge any post-processing view created by solver 1
Default value: 1
Saved in: General.OptionsFileName

Solver.PopupMessages1

Automatically display messages produced by solver 1
Default value: 1
Saved in: General.OptionsFileName

Solver.ClientServer2

Connect solver 2 to the Gmsh server
Default value: 0
Saved in: General.OptionsFileName

Solver.MergeViews2

Automatically merge any post-processing view created by solver 2
Default value: 1
Saved in: General.OptionsFileName

Solver.PopupMessages2

Automatically display messages produced by solver 2
Default value: 1
Saved in: General.OptionsFileName

Solver.ClientServer3

Connect solver 3 to the Gmsh server
Default value: 0
Saved in: General.OptionsFileName

Solver.MergeViews3

Automatically merge any post-processing view created by solver 3
Default value: 1
Saved in: General.OptionsFileName

Solver.PopupMessages3

Automatically display messages produced by solver 3
Default value: 1
Saved in: General.OptionsFileName

Solver.ClientServer4

Connect solver 4 to the Gmsh server
Default value: 0
Saved in: General.OptionsFileName

Solver.MergeViews4

Automatically merge any post-processing view created by solver 4
Default value: 1
Saved in: General.OptionsFileName

Solver.PopupMessages4

Automatically display messages produced by solver 4
Default value: 1
Saved in: General.OptionsFileName

5.2 Solver example

Here is a small example of how to interface a C solver with Gmsh. The following listing reproduces the `utils/solvers/mysolver.c' file from the Gmsh source distribution.

/* $Id: mysolver.c,v 1.4 2004/03/13 21:00:20 geuzaine Exp $ */
/*
 * Copyright (C) 1997-2004 C. Geuzaine, J.-F. Remacle
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy,
 * modify, merge, publish, distribute, and/or sell copies of the
 * Software, and to permit persons to whom the Software is furnished
 * to do so, provided that the above copyright notice(s) and this
 * permission notice appear in all copies of the Software and that
 * both the above copyright notice(s) and this permission notice
 * appear in supporting documentation.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT OF THIRD PARTY RIGHTS. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDER OR HOLDERS INCLUDED IN THIS NOTICE BE LIABLE FOR
 * ANY CLAIM, OR ANY SPECIAL INDIRECT OR CONSEQUENTIAL DAMAGES, OR ANY
 * DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
 * WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
 * OF THIS SOFTWARE.
 * 
 *  Please report all bugs and problems to <gmsh@geuz.org>.
 */

/* This file contains a dummy client solver for Gmsh. It does not
   solve anything, but shows how to program your own solver to interact
   with the Gmsh solver module.
   
   To compile this solver, type something like:

   gcc -o mysolver.exe mysolver.c GmshClient.c
   
   To test this solver, copy the mysolver.opt file into your default
   Gmsh option file, or lauch Gmsh with the command:
   
   gmsh -option mysolver.opt */

/* We start by including some standard headers. Under Windows, you
   will need to install the cygwin tools (http://www.cygwin.com) to
   compile this example (as well as your own solver), since the Gmsh
   solver interface uses Unix sockets. */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>

/* Now we include the Gmsh client interface definitions. At the time
   of this writing, the client interface contains only three
   functions: Gmsh_Connect, Gmsh_SendString and Gmsh_Disconnect. This
   example shows how to use these functions in order to program some
   simple interactions between a solver and Gmsh. */

#include "GmshClient.h"

/* The following typedef defines the two actions of our dummy solver:
   either output some valid option strings, or run a dummy computation
   and output a post-processing map. */

typedef enum { options, run } action;

/* Let's now define some fake CPU intensive functions: */

long worktime()
{
  struct timeval tp;
  gettimeofday(&tp, (struct timezone *)0);
  return (long)tp.tv_sec * 1000000 + (long)tp.tv_usec;
}

void work()
{
  long t1 = worktime();
  while(1) {
    if(worktime() - t1 > 1.e5)
      break;
  }
}

/* And here we go with the main routine of the solver: */

int main(int argc, char *argv[])
{
  action what = run;
  int i = 0, s;
  char *name = NULL, *option = NULL, *socket = NULL, tmp[256];
  FILE *file;

  /* 1. Loop through the command line arguments, remember the action
     the solver has to perform (what) and store the socket name, the
     option name and the problem name. */

  while(i < argc) {
    if(argv[i][0] == '-') {
      if(!strcmp(argv[i] + 1, "socket")) {
        i++;
        if(argv[i])
          socket = argv[i++];
      }
      else if(!strcmp(argv[i] + 1, "options")) {
        i++;
        what = options;
      }
      else if(!strcmp(argv[i] + 1, "run")) {
        i++;
        what = run;
        if(argv[i])
          option = argv[i++];
      }
    }
    else
      name = argv[i++];
  }

  /* 2. If the '-socket' option was not given, we cannot connect to
        Gmsh... */

  if(!socket) {
    printf("No socket specified: running non-interactively...\n");
    exit(1);
  }

  /* 3. Try to connect to the socket given by the '-socket' command
     line option: */

  s = Gmsh_Connect(socket);
  switch (s) {

    /* 3.1. If the socket is <0, issue an error... */

  case -1:
    printf("Couldn't create socket %s\n", socket);
    break;
  case -2:
    printf("Couldn't connect to socket %s\n", socket);
    break;
  default:

    /* 3.2. ...otherwise, send the GMSH_CLIENT_START command (together
       with the process ID of the solver), check if a problem name was
       specified, and decide what to do according to the 'what'
       variable: */

    sprintf(tmp, "%d", getpid());
    Gmsh_SendString(s, GMSH_CLIENT_START, tmp);
    if(!name) {
      Gmsh_SendString(s, GMSH_CLIENT_ERROR, "Missing file name");
      Gmsh_Disconnect(s);
      exit(1);
    }
    switch (what) {

      /* 3.2.1. If what==options, the solver sends the valid options
         (here for the first option): */

    case options:
      Gmsh_SendString(s, GMSH_CLIENT_OPTION_1, "Val1");
      Gmsh_SendString(s, GMSH_CLIENT_OPTION_1, "Val2");
      Gmsh_SendString(s, GMSH_CLIENT_OPTION_1, "Val3");
      break;

      /* 3.2.2. If what==run, the solver runs the chosen option,
         updates the progress message, issues some information data,
         produces a post-processing map and asks Gmsh to merge it: */

    case run:
      sprintf(tmp, "Running %s with option %s...", name, option);
      Gmsh_SendString(s, GMSH_CLIENT_INFO, tmp);
      for(i = 0; i < 10; i++) {
        sprintf(tmp, "%d %% complete", 10*i);
        Gmsh_SendString(s, GMSH_CLIENT_PROGRESS, tmp);
        work();
      }
      sprintf(tmp, "Done with %s!", name);
      Gmsh_SendString(s, GMSH_CLIENT_INFO, tmp);
      file = fopen("mysolver.pos", "wb");
      if(!file) {
        Gmsh_SendString(s, GMSH_CLIENT_ERROR, "Unable to open output file");
      }
      else {
        fprintf(file, "View \"%s\"{\n", option);
	fprintf(file, "ST(0,0,0,1,0,0,0,1,0){0,1,2};\n");
        fprintf(file, "};\n");
        fclose(file);
        Gmsh_SendString(s, GMSH_CLIENT_VIEW, "mysolver.pos");
      }
      break;
    }

    /* 3.3. We can now disconnect the solver from Gmsh: */

    Gmsh_SendString(s, GMSH_CLIENT_STOP, "Goodbye!");
    Gmsh_Disconnect(s);
    break;
  }

  /* 4. That's it! */

}

To define the above solver as the second external solver in Gmsh, you should define the following solver options (either merge them in your Gmsh option file, or use the -option command-line option--see 8.2 Command-line options):

// These options define 'mysolver.exe' as the second solver in Gmsh's
// solver module, under the name 'My C Solver'.
Solver.Name1 = "My C solver";
Solver.Help1 = "A simple example of the client/server 
solver implementation in Gmsh...";
Solver.Executable1 = "./mysolver.exe";
Solver.Extension1 = "";
Solver.MeshName1 = "";
Solver.MeshCommand1 = "";
Solver.OptionCommand1 = "-options";
Solver.FirstOption1 = "Option";
Solver.SecondOption1 = "";
Solver.ThirdOption1 = "";
Solver.FourthOption1 = "";
Solver.FifthOption1 = "";
Solver.FirstButton1 = "Run";
Solver.FirstButtonCommand1 = "-run %s";
Solver.SecondButton1 = "";
Solver.SecondButtonCommand1 = "";
Solver.ThirdButton1 = "";
Solver.ThirdButtonCommand1 = "";
Solver.FourthButton1 = "";
Solver.FourthButtonCommand1 = "";
Solver.FifthButton1 = "";
Solver.FifthButtonCommand1 = "";
Solver.ClientServer1 = 1;
Solver.MergeViews1 = 1;
Solver.PopupMessages1 = 1;

6. Post-processing module

Gmsh's post-processing module can handle multiple scalar, vector or tensor data sets along with the geometry and the mesh. The data sets should be given in one of Gmsh's post-processing file formats described in 9. File formats. Once loaded into Gmsh, scalar fields can be displayed as iso-value lines and surfaces or color maps, whereas vector and tensor fields can be represented either by three-dimensional arrows or by displacement maps. In Gmsh's jargon, each data set is called a "view", and can arbitrarily mix all types of elements and fields. Each view is given a name, and can be manipulated either individually (each view has its own button in the GUI and can be referred to by its index in the scripting language) or globally (see the PostProcessing.LinkView option in 6.3 Post-processing options).

By default, Gmsh treats all post-processing views as three-dimensional plots, i.e., draws the scalar, vector and tensor primitives (points, lines, triangles, tetrahedra, etc.) in 3D space. But Gmsh can also represent each post-processing view containing scalar points as two-dimensional ("X-Y") plots, either space- or time-oriented:

• in a `2D space table', the scalar points are taken in the same order as they are defined in the post-processing view: the abscissa of the 2D graph is the curvilinear abscissa of the curve defined by the point series, and only one curve is drawn using the values associated with the points. If several time steps are available, each time step generates a new curve;
• in a `2D time table', one curve is drawn for each scalar point in the view and the abscissa is the time step.

Although visualization is usually mostly an interactive task, Gmsh exposes all the post-processing commands and options to the user in its scripting language to permit a complete automation of the post-processing process (see e.g. 7.8 `t8.geo', and 7.9 `t9.geo').

The two following sections summarize all available post-processing commands and options. Most options apply to both 2D and 3D plots (colormaps, point/line sizes, interval types, time step selection, etc.), but some are peculiar to 3D (lightning, element selection, etc.) or 2D plots (graph style, labels, etc.). Note that 2D plots can be positioned explicitly inside the graphical window, or be automatically positioned in order to avoid overlaps.

Sample post-processing files in human-readable "parsed" format (see section 9.4 Gmsh parsed post-processing file format) are available in the `tutorial' directory of Gmsh's distribution (`.pos' files).

6.1 Post-processing commands
6.2 Post-processing plugins
6.3 Post-processing options

6.1 Post-processing commands

Combine TimeSteps;

Combines the data from all the post-processing views having the same name into new multi time step views.

Combine Views;

Combines all post-processing views in a single new view.

Delete View[expression];

Deletes (removes) the expression-th post-processing view. Note that post-processing view numbers start at 0.

Duplicata View[expression];

Duplicates the expression-th post-processing view.

Plugin (string) . Run;

Executes the plugin string. The list of default plugins is given in 6.2 Post-processing plugins.

Plugin (string) . string = expression;

Sets a floating point option for a given plugin. See 7.9 `t9.geo', for some examples.

Save View[expression] char-expression;

Saves the the expression-th post-processing view in a file named char-expression.

View "string" { string ( expression-list ) { expression-list }; ... }

Creates a new post-processing view, named "string". This is the easiest way to create a post-processing view, but also the least efficient (the view is read through Gmsh's script parser, which can become quite slow if the view is large--e.g. with more than 100,000 elements). Though, this "parsed" post-processing format (explained in detail in 9.4 Gmsh parsed post-processing file format) is very powerful for testing proposes, since all the values are expressions. Two other formats, better adapted for large data sets, are described in 9.2 Gmsh ASCII post-processing file format and 9.3 Gmsh binary post-processing file format.