> Dear GetFEM++ users, > > I would like to play around with transport equations and while writing the > questions below I realised that the stiffness matrix will not be > symmetrical. So before we start: can GetFEM calculate the non-symmetric > stiffness matrix? There is no need to solve the linear system. From the > mailing list it seems that the answer is no.
I have done thermo-elastic coupling in GetFEM which gives non-symmetric tangent matrix and there was no problem with it. Could you pleas indicate to which posting in the mailing list are you referring? > NO: can you suggest any other FEM package that can handle > these kind of equations in more than 3 dimensions? > > YES: Please read on. > > I would like to play around a little bit with the Fokker-Planck (FP) > equation: (a PDE that has many names so you may recognise is as (at > least similar to) Klein-Kramers, Liouville, Boltzmann-transport > equation etc ...). However, I have limited experience with FEM and > thus problems in deciding whether or not FEM is the way to go and to > decipher the user manual. You have indicated that you would like to solve problems in space with dimension > 3. I might be wrong but besides selecting FEM solver you may encounter problems generating n-dimensional discretisation of the space (triangulation) unless the space is simple hypercube (though some tools can handle n-dimensional space, if I recall correctly qhull for instance). "whether or not FEM is the way to go" is a good question. Personally given a PDE to solve I would ask myself if I need unstructured meshes for any reason. If so (for instance to handle complex geometries, to capture discontinuities in solution or initial data) then yes, FEM might be a way to go. Otherwise if I can go with topologically regular meshes and the solution is fairly regular I would consider sort of FDM. I would look at the above question not purely from the point of view of numerical methods but considering the issue : what is the advantage of investing in new software tools, especially if I can solve the problem with the means I already have. If the drive is scientific curiosity, the yes, I can go, but otherwise pragmatic approach seems to be most fruitful. It may sound a bit bitter but biggest deficiency of most of the software packages is the insufficient support in overcoming steep learning curves. In most cases this is not the fault of the authors of the tools but a tip of a more general problem (and a topic for separate long discussion). > The main question: > 0: Can the GetFEM++ handle the first order derivatives? Do they not give a > non-symmetric stiffness matrix? As I mentioned I do not see that a lack of symmetry of the tangent matrix is any problem for GetFEM. > 1: How do I enter the first order derivative terms, i.e., A.grad(u) terms? > Where A is a vector or vector field. (Preferentially in the python > interface) This is possible in C++ interface, but unfortunately I cannot comment if also in the Python interface. Regards, Roman -- Roman Putanowicz, PhD < [email protected] > Institute for Computational Civil Engng (L-5) Dept. of Civil Engng, Cracow Univ. of Technology www.l5.pk.edu.pl, tel. +48 12 628 2569, fax 2034 _______________________________________________ Getfem-users mailing list [email protected] https://mail.gna.org/listinfo/getfem-users
