Describing the mesh programmatically

Describing the mesh inside the FreeFem++ program is very handy. Once this is done, changing the shape of the mesh or the size of elements is reduced to changing a parameter value. It can be done in 2D and 3D, but it only works easily in 2D. In the FreeFem++ documentation, everything is described in chapter Mesh Generation.

External CAD tools

In 3D, meshes can be still be defined and generated in the FreeFem++ program, but taking care of all the details (especially when intersections of surfaces are involved) becomes a nightmare. So it is advised to use an external CAD tool like Gmsh. Here is how (thank you to PP for trying this out) :

• Draw geometry and build the mesh in Gmsh. Then export it to the Medit format.
• Find the numeric labels of the boundaries which will need a boundary condition (e.g. by loading the mesh in Medit and displaying the material properties of hand-picked points on the boundaries).
• Load the mesh into the FreeFem++ program with readmesh3().

For learning purposes it may be sufficient to build meshes out of basic geometrical shapes like cubes and spheres. Please check the list of FreeFem++ 3D examples in case one of them suits your needs.

• bold black : all standard FreeFem++ keywords.
• blue : user-defined objects. User-defined types are in bold face. Character strings are in "dark blue".
• green : macros and include files.
• bold red : spelling mistakes, syntax errors, undefined objects, macros and include files containing errors. In the above example (click for a bigger image) there are two mistakes : "plotx" does not exist (it should be "plot") and "f" is not defined because it was mistyped as "fx".
• purple : comments.
• Once you have a coherent program, you can run it just by clicking on a button (no need to save it) and if FreeFem++ produces a error the problematic line will be highlighted.

Simply use the plot() command with 3D data :

All VTK classes are potentially usable. But it's not realistic to reimplement Paraview inside FreeFem++-cs. So please let me know what graphical functionalities you need (e.g. through the comment form below). Here is the current list of available graphical options :

All options will eventually be modifiable from the FreeFem++ program through plot() options.

The official FreeFem++ documentation (which doubles as the FreeFem++ book) can be accessed in many different ways :

• As a PDF :
  http://www.freefem.org/ff++/ftp/freefem++doc.pdf
• As HTML, both from inside FreeFem++-cs and from the web :
  http://www.ljll.math.upmc.fr/lehyaric/ffcs/doc/ff/ffdoc.html
• Through a quick reference card : following a request made during the 2009 FreeFem++ workshop, I have summarized all FreeFem++ keywords on one page for quick reference. Each keyword is linked to the relevant chapters of the FreeFem++ documentation when available :
  http://www.ljll.math.upmc.fr/lehyaric/ffcs/refcard.php (by the way, anyone willing to help me add \index{} flags into the documentation is very welcome)
• You will find more documents on the Manuals web page.

Asking questions to the community

• Mailing list for the FreeFem++ language and its command-line version :
  http://www.ljll.math.upmc.fr/cgi-bin/mailman/listinfo/freefempp
• Dialoguing about FreeFem++-cs : with the comment form at the bottom of most pages on the FreeFem++-cs web site.

3D graphical tools

Here are some 3D graphical tools that may become useful when developing more powerful simulations.

• Medit : How to link FreeFem++ and Medit : link with medit in the FreeFem++ documentation. The full Medit documentation is accessible from FreeFem++-cs or online at Medit documentation.
• VTK output : very useful to connect to e.g. Paraview. The trick is to save FreeFem++ data into the VTK format. See for example FreeFem++ iovtk.cpp load module example or use "File/Save Image As.../VTK" in FreeFem++-cs.
• Gmsh : you may have already used Gmsh as a CAD tool to generate a 3D mesh. Since Gmsh also contains a very nice visualisation module, you may find it useful to plug FreeFem++ output back into Gmsh. See for instance http://www.geuz.org/pipermail/gmsh/2010/005844.html.

Editors

The FreeFem++-cs editor has one big advantage for new users : it highlights mistyped variables in red. Apart from that, it will never have as many features as a complete development editor (Emacs anyone?). FreeFem++-cs can deal with a program text edited in an external editor :

• "File/Auto Reload" to reload a file into FreeFem++-cs automatically when it has been changed externally.
• "Compute/Auto Run" to run a newly reloaded program text automatically.
• "Edit/Hide Editor Panel" to put the unused internal editor window out of sight and make more space for the graphics window.

Load modules

FreeFem++ "load modules" are dynamic libraries written in C++. Because of the universal nature of C++, load modules can be used to implement any functionality missing from FreeFem++. The downside is that it can be very complicated to implement. Basically only FH creates new load modules, everyone else only modifies existing ones.

Compiling FreeFem++ load modules requires "ff-c++", which is not included in the FreeFem++-cs package at the moment ("ff-c++" is very precise on where the different headers and object files have to be, so I have not tried to follow these constraints in FreeFem++-cs). If you need to develop modules, you need to switch to plain FreeFem++. Once the module is built, you may return to FreeFem++-cs to use it.

Parallel programming

Multicores are supported automatically throught the use of numerical libraries capable of Shared Memory Parallelism (e.g. multithreaded ATLAS). Distributed Memory Parallelism (several distinct machines working together) is also possible but it requires MPI programming.

As of this writing (September 2010), the default precompiled version of FreeFem++-cs does not include a multithreaded BLAS version, and does not run MPI programs either. If you want to run parallel programs, you need to download and compile FreeFem++ with the correct configuration options. Please check MPI programming in FreeFem++.

When simulations become too resource-intensive for the local machine, computations can be run through ssh on a remote server where FreeFem++-cs is installed, through "Options/Remote server" and "Options/Other Options.../Remote server command". The local machine must still be powerful enough to display the resulting graphics.

Through the years, the obvious selling point for FreeFem++-cs has been its single window. Its simplicity appeals to newcomers.

FreeFem++-cs could be improved in many ways, but stability and quality control will be our first focus now that 3D is implemented.

Thank you for your interest in FreeFem++-cs!