Dear Umut, Is it possible that the error comes from the MUMPS interface ? What kind of sparse matrix do you use ?
Yes, you can send me the program, I will try to check. Yves. On mercredi 19 octobre 2011, Umut Tabak wrote: > On 10/19/2011 10:29 AM, Umut Tabak wrote: > > Dear all, > > > > I have run into a problem today with the gmm++ library. I am not very > > sure where the problem could be. I coded a symmetric lanczos solver > > for my problem and used gmm++ and MUMPS (as the linear solver). > > However, the accuracy of the basic linear algebra operations > > matrix-vector product and gmm::add, scale and so seem to be > > questionable to me. > > > > Well it could be a bit cryptic to understand for you, maybe, but let > > me rephrase with an example: > > > > I am computing some coefficients to form a tridiagonal matrix and > > these coefficients that I compute in gmm++ start to deviate from the > > ones I computed in MATLAB. They seem to be the same at the starting > > iterations then conducting these matrix-vector operations(for > > orthogonalizations), they start to diverge, I am not sure what the > > problem could be. > > > > I went over my code several times, however, the end results tell me > > that there is indeed a problem in the orthogonalization phase, which > > is basically a combination of matrix-vector operations. > > > > Any comments are appreciated on this issue. > > > > Best regards, > > Umut > > As a reply to my own post, there is definitely a problem in the linear > algebra operations in gmm++ from accuracy point of view. > > I tested my problem with MTL4 and the results seem to be far more close > to what they should be. > > I am not sure what the problem is in gmm++ but this deserves some > attention. > > I can provide a test case in MATLAB and gmm++ where I compare these > tridiagonal coefficients of the lanczos proces. To test the MATLAB code, > one should have the MUMPS MATLAB interface installed. > Best regards, > Umut -- Yves Renard ([email protected]) tel : (33) 04.72.43.87.08 Pole de Mathematiques, INSA-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
