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$Id: FAQ,v 1.54 2005-03-03 15:07:29 geuzaine Exp $
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Gmsh is an automatic three-dimensional finite element mesh generator,
facilities. Its design goal is to provide a simple meshing tool for
academic problems with parametric input and advanced visualization
capabilities.
License. See the file doc/LICENSE for more information, or go to the
GNU foundation's web site at http://www.gnu.org.
* 1.3 What does 'Gmsh' mean?
<http://www.geuz.org/gmsh/> is the primary location to obtain
information about Gmsh. You will for example find a complete reference
manual as well as a searchable archive of the Gmsh mailing list
(<gmsh@geuz.org>) on this webpage.
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Gmsh is known to run on Windows 95/98/NT/2000/XP, Linux, Mac OS X,
Compaq Tru64 Unix (aka OSF1, aka Digital Unix), Sun OS, IBM AIX, SGI
IRIX, FreeBSD and HP-UX. It should compile on any Unix-like operating
system, provided that you have access to a recent C and C++ compiler.
You should have the OpenGL libraries installed on your system, and in
the path of the library loader. A free replacement for OpenGL can be
found at <http://www.mesa3d.org>.
* 2.3 What do I need to compile Gmsh from the sources?
You need a C and a C++ compiler (e.g. the GNU compilers gcc and g++)
as well as the GSL (version 1.2 or higher; freely available from
http://sources.redhat.com/gsl/) and FLTK (version 1.1.x, configured
with OpenGL support; freely available from http://www.fltk.org).
You'll also need the jpeg library if you want to save jpeg images, and
the libpng and zlib libraries if you want to save png images.
Under Windows, you will need the Cygwin tools and compilers (freely
available from http://www.cygwin.com), as well as "cygwin-enabled"
version of FLTK (i.e., you have to configure FLTK with "./configure
--enable-cygwin").
If you change some configuration options (type ./configure --help to
get the list of all available choices), don't forget to do 'make
clean' before rebuilding Gmsh.
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* 3.1 Gmsh [from a binary distribution] complains about missing
libraries.
Try 'ldd gmsh' (or 'otool -L gmsh' on Mac OS X) to check if all the
required shared libraries are installed on your system. If not,
install them. If it still doesn't work, recompile Gmsh from the
sources.
* 3.2 Gmsh keeps re-displaying its graphics when other windows
partially hide the graphical window.
Disable opaque move in your window manager.
* 3.3 The graphics display very slowly.
Are you are executing Gmsh from a remote host (via the network)
without GLX? You should turn double buffering off (with the -nodb
command line option).
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* 4.2 Gmsh is very slow when I use many transformations (Translate,
Rotate, Symmetry, Extrude, etc. ). What's wrong?
The default behavior of Gmsh is to check and suppress all duplicate
entities (points, lines and surfaces) each time a transformation
command is issued. This can slow down things a lot if many
transformations are performed. There are two solutions to this
problem:
- you may save the unrolled geometry in another file (e.g. with
gmsh file.geo -0 > flat.geo), and use this new file for subsequent
computations;
- you may set the 'Geometry.AutoCoherence' option to 0. This will
prevent any automatic duplicate check/replacement. If you still
need to remove the duplicates entities, simply add 'Coherence;' at
strategic locations in your geo files (e.g. before the creation of
line loops, etc.).
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- in the interface: Tools->Options->Mesh->2D->Isotropic algorithm (Triangle)
integrated in the new ones, so please don't send bug reports on the
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old algorithm anymore.
Send us your geometry, and we will investigate. Please keep the
following in mind though: 2D (surface) meshes are generated by
projecting the 2D mesh in a "mean plane" of the surface. This gives
nice results only if the surface curvature is small enough. Otherwise
you must cut the surface into several pieces (patches). For example,
using half circles to define a cylinder will fail with the
unstructured algorithm: you should define arcs with angles smaller
than Pi, and thus define the cylinder with at least three patches.
The 3D algorithm is still very experimental. Try to change some
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characteristic lengths in your input file to generate meshes that
better suit the geometrical details of your structure.
* 5.4 I changed the characteristic lengths, but the 3D algorithm still
does not work. What should I do?
Buy a professional mesh generator ;-) You can also try to use Netgen
instead of the default algorithm for the 3D mesh. Note that all
surface meshes have to be oriented with exterior normals in this case.
We are working on it. But since we have a (very) limited amount of
time to spend on the development of Gmsh, this may take a while. For
very big meshes, see the answer to the previous question...
* 5.6 The quality of the elements generated by the 3D algorithm is
very bad.
Upgrade to Gmsh >= 1.54 and use "Optimize quality". If badly shaped
elements still exist due to the surface recovery step, you can try to
use Netgen instead of the default algorithm for the 3D mesh. Note that
all surface meshes have to be oriented with exterior normals in this
case.
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The swapping algorithm is not very clever at the moment. Try to change
the surface mesh a bit, or recombine your mesh to generate prisms or
* 5.8 Tools->Visibility does not seem to work with extruded meshes.
This is fixed in Gmsh >= 1.54. However, when region numbers are
explicitly assigned to mesh entities in the extrude commands (which
partially destroys the geometry/mesh relationship), the Visibility
tool will only work as expected when displaying Elementary
entities. In this particular case, the only solution to visualize
extruded Physical entities is to save the mesh, and to read it again.
* 5.9 Does Gmsh support curved elements?
Yes, Gmsh can generate both 1st order and 2nd order elements. To
generate second order elements, click on 'Second order elements' in
the mesh menu after the mesh is completed. To always generate 2nd
order elements, select 'Generate second order elements' in the mesh
option panel. From the command line, you can also use '-order 2'.
* 5.10 Can I import an existing surface mesh in Gmsh and use it to
build a 3D mesh?
Yes, either in the form of a STL triangulation, or by using the
"Discrete Surface" commands. Note that Gmsh cannot currently modify
the surface mesh you provide in this way, so the surface mesh has to
be conform (without gaps, hanging nodes, etc.) and must contain
surface elements having the (final) desired sizes.
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If you want to simply launch a program from within Gmsh, just edit the
options to define your solver commands (e.g. Solver.Name0,
Solver.Executable0, etc.), and set the ClientServer option to zero
If you want your solver to interact with Gmsh (for error messages,
option definitions, post-processing, etc.), you will need to link your
solver with the GmshClient routines and add the appropriate function
calls inside your program. You will of course also need to define your
solver commands in an option file, but this time you should set the
ClientServer variable to 1 (e.g. Solver.ClientServer = 1). C, C++,
Perl and Python solver examples are available in the source
distribution in the utils/solvers directory.
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executable. What's wrong?
The solver executable (for example, 'getdp.exe') has to be in your
path. If not, simply go to the solver options (for example,
Solver->GetDP->Options->Executable) to specify its location.
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On recent versions of Microsoft Windows (XP SP2), it seems that you
need to execute the solver (e.g. launch 'getdp.exe') at least once
* 6.3 Can I launch Gmsh from my solver (instead of launching my solver
from Gmsh) in order to monitor a solution?
Sure. A simple C program showing how to do this is given in
'utils/misc/callgmsh.c'.
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* 7.2 Can I save isosurfaces to a files?
Yes: first run the CutMap plugin to extract the isosurface, then use
'View->Save As' to save the new view.
* 7.3 Can Gmsh generate isovolumes?
Yes, with the CutMap plugin (set the extractVolume to -1 or 1 to
extract the positive or negative levelset).
* 7.4 How do I animate my plots?
If the views contain multiple time steps, you can press the 'play'
button under the graphic window, or change the time step by hand in
the view option panel. You can also use the left and right arrow keys
to change the time step in all visible views in real time.
If you want to loop through different views instead of time steps, you
can use the 'Loop through views instead of time steps' option in the
view option panel, or use the up and down arrow keys.
Load a vector view containing the displacement field, and set 'Vector
display' to 'Displacement' in View->Options->Aspect. If the
displacement is too small (or too large), you can scale it with the
'Displacement factor' option. (Remember that you can drag the mouse in
all numeric input fields to slide the value!)
Another option is to use the "general transformation expressions" (in
View->Options->Offset) on a scalar view, with the displacement map
selected as the transformation data source.
Yes, there are several ways to do that.
The easiest is to load two views: the first one containing a
displacement field (a vector view that will be used to deform the
mesh), and the second one containing the field you want to display
(this view has to contain the same number of elements as the
displacement view). You should then set 'Vector display' to
'Displacement' in the first view, as well as set 'Data source' to
point to the second view. (You might want to make the second view
invisible, too. If you want to amplify or decrease the amount of
deformation, just modify the 'Displacement factor' option.)
Another solution is to use the "general transformation expressions"
(in View->Options->Offset) on the field you want to display, with the
displacement map selected as the transformation data source.
And yet another solution is to use the DiplacementRaise plugin.
* 7.7 Can I color the arrows representing a vector field with data
from a scalar field?
Yes: load both the vector and the scalar fields (the two views must
have the same number of elements) and, in the vector field options,
* 7.8 Can I color isovalue surfaces with data from another scalar
* 7.11 Can I do arithmetic operations on a view? Can I perform
operations involving different views?
Yes, with the Evaluate plugin.
* 7.12 Some plugins seem to create empty views. What's wrong?
There can be several reasons:
- the plugin might be written for specific element types only (for
example, only for scalar triangles or tetrahedra). In that case, you
should transform your view before running the plugin (you can use
Plugin(DecomposeinSimplex) to transform all quads, hexas, prisms and
pyramids into triangles and tetrahedra).
- the plugin might expect a mesh while all you provide is a point
cloud. In 2D, you can use Plugin(Triangulate) to transform a point
cloud into a triangulated surface. A 3D version of this plugin is
not available yet but it is on our TODO list.
- the input parameters are out of range.
In any case, you can automatically remove all empty views with
'View->Remove->Empty Views' in the GUI, or with "Delete Empty Views;"
in a script.