Hello. I'm using slepc and I'm trying to do a stability analysis on a solid mechanics problem which in my case is associated with looking at the highest real part of the eigenvalues of the general problem Ax=?Bx. My problem has a real non-symmetric A and a positive definite B. When I try to ask for the largest real eigenvalues it takes a great number of iterations to solve the problem, especially when I reach the yielding phase of my problem, in which case I can no longer obtain the required eigenvalues.
The eigenvalues on the first steps are similar to what I obtained in Matlab for largest magnitude (Matlab doesn't converge for the largest real option). These eigenvalues are purely imaginary. When I was doing a standard eigenvalue analysis on this problem I found that I could greatly increase my performance with a Shift-Invert transformation. However, when I try the SI in the general case I get the following error: [0]PETSC ERROR: Error in external library! [0]PETSC ERROR: Error in Lapack xHSEQR 25! I'm using umfpack to do a preonly LU solve. Preconditioned Eigensolvers seem not to converge at all so for now I'm stuck with these. When I removed the umfpack I got the following error: [0]PETSC ERROR: Detected zero pivot in LU factorization: see http://www.mcs.anl.gov/petsc/documentation/faq.html#ZeroPivot! [0]PETSC ERROR: Zero pivot row 0 value 0 tolerance 2.22045e-14! Based on the FAQ I tried using -st_pc_factor_shift_type POSITIVE_DEFINITE. While this made sinvert not crash and converge fast it also messed with my eigenvalues. Any ideas on how I could solve this? Thank you so much, Miguel Arriaga
