[Octave-bug-tracker] [bug #58926] Octave gives wrong results with intel-mkl when diagonalizing large matrices

[Archisman Panigrahi]

Follow-up Comment #8, bug #58926 (project octave):


[comment #6 comment #6:]
> @OP: That is enough information to localize that the bug is not within
Octave, since openblas gives the correct answer.
> 
> If you type
> 
> export MKL_THREADING_LAYER=gnu
> 
> at the bash prompt before invoking Octave, does the error go away? If so,
that would confirm that the error is between IOMP and GOMP. The MKL was given
a Gnu compatibility mode to solve that problem.
> 
I confirm that this workaround works. 

However, users who are using MKL with Octave should be somehow notified about
this bug. This issue only pops up when the size of matrices is sufficiently
big, and this may go unnoticed (having using Octave for several years, I
always believe its results, and so would most other users). I only noticed the
issue after plotting a graph of something, which seemed to be wrong.

This issue and its workaround should be mentioned in the Octave Wiki. Right
now, it is can only be found in some Debian bug reports (not mentioned in
MKL's website at all, and I could not find it anywhere else in the web), so it
is hard to find. And users normally would not double check results produced by
Octave.

I feel the severity of this bug should be increased from Normal to Very High
(it is not exactly a Octave bug, but it ends up affecting  Octave severely.
Scilab remains unaffected by this issue. Also, I don't know whether I am
allowed to do change the severity of the bug myself. I could not find how to
do it.), and this bug report should not be closed until this issue is
mentioned in the Octave Wiki.

> If that workaround works, add the "export" line to your .bashrc file and
Octave will work with MKL without surprises.

Yes, this works.

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