Re: inv function failing?

On Sun, Dec 4, 2022 at 4:05 PM Enzo Alberto Dari <[email protected]>
wrote:

> While upgrading my debian OS from 10.x to 11.x (octave 4.4.5 to 6.2.0),
> one of my scripts started failing. I managed to create a simple test
> (attached if the mailing list doesn't block it) that reproduces the problem.
> The matrix is blocked, so there is an alternate method to compute its
> inverse by blocks that always works. This test verifies if the computed
> inverse times the original matrix has condition number 1 (as it should be
> for the identity matrix).
> To make things more complicated, I ran the test in 5 machines with debian
> 11.5 (octave 6.2.0) and it failed in 3 of them, working ok in the other 2.
> Perhaps something to do with new processor features? (apparently is failing
> in machines with "newer" processors):
> Intel(R) Core(TM) i5 CPU         750  @ 2.67GHz: Ok.
> Intel(R) Core(TM) i7-4930K CPU @ 3.40GHz: Ok.
> Intel(R) Core(TM) i5-1035G1 CPU @ 1.00GHz: Fails.
> Intel(R) Core(TM) i9-7900X CPU @ 3.30GHz: Fails.
> Intel(R) Core(TM) i9-9900X CPU @ 3.50GHz: Fails.
>
> Any clue about what may be happening?
> Any tips for further analysis?
> Thanks in advance,
>
>
This mailing list is pretty much dead -- you should post on discourse.
In any case, what do you mean "fail"? Crash, core dump, or just a wrong
answer?
I would guess that the issue is with openblas libraries
provided by debian. You can try to override them with reference blas
by starting octave as
LD_PRELOAD=/usr/lib64.libblas.so octave
(adjust the path to libblas as appropriate)
And you should fill the bug against the debian package.

Your script works on i9-9880 and ryzen-9 3950 (on Fedora 37):
octave:1> chkBlockedInverse
sizeb = 19
rankb = 19
diffinvs = 3.3156e-17
ans = 1.0000
ans = 1.0000
ans = 1.0000
ans = 1.0000
diffinvs_ = 3.3156e-17
ans = 1.0000
ans = 1.0000
ans = 1.0000
ans = 1.0000
octave:2>




-- 
> Enzo A. Dari
> Profesor Titular
> Instituto Balseiro <http://www.ib.edu.ar/>
>

Dmitri.
-- 

>
>
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