[petsc-users] [slepc] nan output for eigenvectors

Patrick Alken patrick.alken at geomag.info
Tue Sep 6 23:18:41 CDT 2022

I sometimes get Nan output values in computed eigenvectors for the
generalized symmetric eigenvalue problem produced by slepc. Is this a known
issue, and is it related to the conditioning of the matrix pair (A,B)? Is
there some way to compute a "condition number" of the matrix pair ahead of
time to see if i have a good chance of getting stable eigenvectors out?

In a possibly related issue, i am finding that petsc/slepc compiled with
debugging vs optimization can produce very different eigenvectors for the
same problem, while the eigenvalues are the same. The eigenvectors seem
more accurate when I use the debugging version of the libraries. Could this
be also a conditioning problem with the matrix pair?
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