Le 04-juin-08 à 16:01, Yves Renard a écrit : > On Wednesday 04 June 2008 10:30, Sébastien Janas wrote: >> Hi all, >> >> I want to solve the transient linear equation of diffusion. >> >> It seems that there is no function pre-build in getfem for the >> transient problems. So I assemble the mass matrix (MM) and stiffness >> matrix (SM) "manually", and then construct the linear system A*X=B >> using the backward euler >> >> A = (MM + delta t * SM) >> B = MM * X(t-1) >> >> Then I have to impose dirichlet conditions on the surface. I import >> my >> mesh from gmsh, where the surface are tagged with a number (in my >> case >> 200). How can I modify my linear system to take into accompt the >> dirichlet conditions? All the functions I found in the documentation >> are in the case where you use model bricks or standard assembly >> procedures... >> >> If I can have the list of node numbers tagged by 200 I would use the >> penalty method. But I am not able to obtain these list. >> >> I am using the python interface of getfem. >> >> Thanks for your help, >> >> Best regards, >> >> Janas Sébastien > > > This is true that there is no general strategy proposed for transient > problems, especially with the matlab or python interfaces. This is > however > not easy to build such a general strategy since the situation can > vary a lot > for differente time integration schemes. > > > However, You can have the list of nodes on a boundary with the command > > gf_mesh_fem_get(MF, 'dof on region', [bnum]); > > > but you have first to tag the boundary with the command > > gf_mesh_set(M, 'region', int bnum, imat CVFLST); > > (see the Matlab examples). > > Yves.
Is there any systematic procedure to impose the dirichlet conditions on my system A*X=B ? I have tried with the penalty method, but the sparse matrix format included in getfem set it very difficult (we can't make B[i] += A[i,i] * BIG * val because A[i,i] give an 1x1 array and not a scalar...) > > > > -- > > Yves Renard ([EMAIL PROTECTED]) tel : (33) > 04.72.43.87.08 > Pole de Mathematiques, INSA de Lyon fax : (33) > 04.72.43.85.29 > 20, rue Albert Einstein > 69621 Villeurbanne Cedex, FRANCE > http://math.univ-lyon1.fr/~renard > > --------- > _______________________________________________ Getfem-users mailing list [email protected] https://mail.gna.org/listinfo/getfem-users
