Hi David, Thank you very much for reply!
I have checked the lapack documentation and the respective petsc C-files beforehand but it did not help very much. I am solving the eigenvalue problem to compute the constant in the trace theorem and hence the matrix A is associated with the integral on the boundary. I do not only get an error when I increase the number of grid elements but also when I decrease the part of the boundary over which I integrate. As I decrease in both cases the ratio between non-zero and zero elements in the matrix, I was wondering if Lapack might have problems with the fact that A has only very few non-zero elements? I am actually using KRYLOVSCHUR now and that works well, but I was just curious why Lapack causes an error. Thanks, Kathrin Hi Kathrin, I'm not sure why lapack would fail here, you could try to look up that error "Error in Lapack xGGES 260" in the lapack documentation? In my experience, lapack works robustly unless the problem is "too large": lapack treats the matrices as dense, so you "hit a wall" at some point and have to go to krylov subspace eigensolvers in slepc instead. But it doesn't sound like your meshes are too large here. It sounds like you're having issues for anything bigger than a 5x5 mesh, right? You could try to use one of slepc's krylov subspace eigensolvers (e.g. LANCZOS, ARNOLDI or KRYLOVSCHUR) to see if that works better? Also, you may already know this, but just in case: You can write libMesh matrices out using matrix->print_matlab(), and then read them into matlab --- you might find this helpful for comparing the matlab vs. slepc results for the larger meshes. David ------------------------------------------------------------------------------ Managing the Performance of Cloud-Based Applications Take advantage of what the Cloud has to offer - Avoid Common Pitfalls. Read the Whitepaper. http://pubads.g.doubleclick.net/gampad/clk?id=121054471&iu=/4140/ostg.clktrk _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
