Hi Shawn,
Yes, this may be the case. Lapack is somehow trying to invert a singular matrix. Could you provide a small test case? I’ve just tried solving a mixed eigenvalue problem and it worked…
Thank you very much Christopher. I think the ArnoldiSolver is working well. I realized the problem is possibly that I didn’t update ngsolve to the latest version…
I currently have trouble updating ngsolve since I accidentally deleted mac-based-python2.7!