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[Octave-bug-tracker] [bug #53700] eigs test failure related to ARPACK ge

From: Dan Sebald
Subject: [Octave-bug-tracker] [bug #53700] eigs test failure related to ARPACK generating real NaN rather than complex NaN+1i*NaN
Date: Tue, 24 Apr 2018 13:39:40 -0400 (EDT)
User-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:55.0) Gecko/20100101 Firefox/55.0

Follow-up Comment #30, bug #53700 (project octave):

The warning can be turned off with:

warning ("off", "Octave:eigs:UnconvergedEigenvalues", "local");

So the suggestion of

+%! d = eigs (A, floor((length(A)-1)/2), "sm", opts);

won't work.  How about floor(length(A)/4) rather than floor((length(A)-1)/2)? 
That would put the NEV somewhere in the middle of the range where the Krylov
subspace isn't adequate.

It's up to Marco to make the choice.  Check for real/imaginary or pick an NEV
somewhere that generates lots of 1.0+-iZi and NaN+iNaN.  Probably doesn't
matter too much.  We're seeing so much variation in the convergence behavior
for all the different libraries and compilers out there.


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