[Octave-bug-tracker] [bug #42743] Inconsistent linear algebra results - openblas bug?

[Ceral Paquet]

Follow-up Comment #5, bug #42743 (project octave):

Ok I spoke too soon - now it's not working.

I trimmed the code down a little and manage to get a panic consistently rather
than inconsistent results.

octave:1> weird_bug
ans = done1
ans = done2
ans = 0
ans = 0
ans = 0
octave:2> weird_bug
ans = done1
ans = done2
panic: Segmentation fault -- stopping myself...
attempting to save variables to 'octave-workspace'...
save to 'octave-workspace' complete
Segmentation fault

The crash always happens on the 2nd run. The code that causes it is below. 

%-------------------------------%
clear

load data

[U S V] = svd(A);
'done1'

[U2 S2 V2] = svd(A);
'done2'

norm(U-U2)
norm(S-S2)
norm(V-V2)
%-------------------------------%

I've found that doing the "small" SVD, i.e. svd(A,0), does not cause a problem
only the full version. The crash seems to occur in norm(U-U2,'fro').

Also, this is with OpenBLAS 0.2.9 and OpenBLAS 0.2.10.rc2. It doesn't happen
with ATLAS or reference implementations - I am posting a bug report to the
OpenBLAS team.

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