Check ARPACK error

[vtraag]

There are a few tests that show intermittent errors ARPACK error. -- No shifts could be applied. This issue has already been investigated before, but never resolved. This issue is to keep track of it, and try to adress it.

I will try to look up what we have done/looked at before, and link/report here whenever relevant.

[szhorvat]

I recommend trying with ARPACK 3.9.1 (but not 3.9.0 which is known to have issues). CC @xylar

[xylar]

It looks like the arpack maintianers could use some help:
conda-forge/arpack-feedstock#49
there hasn't been much recent progress. I'm not expert enough in c/c++ libraries in general to want to volunteer. If either of you know of anyone you could send over, that would likely really speed up how soon we could move to arpack 3.9.1.

[szhorvat]

Actually, ARPACK is a Fortran library, which makes the pool of potential maintainers even smaller.

[xylar]

Ah, yeah, I'm about equally unhelpful there.

[xylar]

Just a note that I skipped 2 more tests in #82 that were causing trouble. We should re-enable everything (remove the patch) as soon as a new ARPACK is available.