I'm using PSSYEVX to get the eigenvalues and eigenvectors of large matrices. Things seem to be working okay...except for this issue with PSLAMCH. I'm using it (as recommend in the PSSYEVX documentation) to determine the tolerance:
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(I've tried 's' as well.)
The problem is that PSSYEVX returns INFO=2, indicating that not all eigenvectors converged. When I check ABSTOL, I see that it equals zero. The documentation indicates that this is not an optimal value -- but how do I choose an appropriate value? Why would PSLAMCH return a value of zero?
Also, even though INFO=2, all of the elements of IFAIL are zero.