Thank you for a nice welcoming message to the email list! (and sorry for the slow reply, meetings ...)
> Posted by Roman Putanowicz on May 20, 2011 - 03:04: > >> 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? See last question (not very conclusive) ... https://mail.gna.org/public/getfem-users/2008-05/msg00011.html >> 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). In the specific problem I'm looking at I have a regular mesh with 2 independent cylinder coordinates (2 x 2D), i.e., r_1,2 and fi_1,2. Now I could simply transform the PDE to cylindrical coordinates and use a finite difference method. However, for this problem and learning for the future I'd prefer to just keep Cartesian coordinates -> curved boundaries. I'll be fine with Mesh.add_point(). > "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. 1: Python lowers the time investment hugely (as does matlab). I'm not that scared of the time investment. 2: I'm curious about the FEM. Since I come from a quantum chemistry background I see the similarities, i.e., using a basis and projecting the solution to the space spanned by the basis. I think this is the way to go and I have the experience with bases formed by radial functions*spherical harmonics. The FEM community has a lot of code and experience with localized basis sets. This I think will be worthwhile to learn. >> 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. A hint on how it would be entered in the C++ interface? I can then dig into the documentation. Thanks again and have a nice weekend. - Magnus ----------------------------------------------- Magnus Paulsson Assistant Professor School of Computer Science, Physics and Mathematics Linnaeus University Phone: +46-480-446308 Mobile: +46-70-6942987 _______________________________________________ Getfem-users mailing list [email protected] https://mail.gna.org/listinfo/getfem-users
