Re: inv function failing?

I narrowed it down to the pthreads version of libopenblas:
LD_PRELOAD=/usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblas.so.0
octave-cli chkBlockedInverse.m
gives incorrect results, while
LD_PRELOAD=/usr/lib/x86_64-linux-gnu/openblas-openmp/libopenblas.so.0
octave-cli chkBlockedInverse.m
works ok.
In Debian both packages: libopenblas0-pthread and libopenblas0-openmp can
be installed in the same system, the default being managed by tne
"alternatives system", but can also be selected manually as above.
I will file a bug report against the libopenblas0-pthread package.
Thanks again, the tip about blas libraries and LD_PRELOAD was really
helpful.
Enzo

On Sun, Dec 4, 2022 at 9:11 PM Enzo Alberto Dari <[email protected]>
wrote:

> Thanks Chris, Dmitri.
> Indeed, the correct behaviour is all condition numbers equal to 1. The
> matrix has the form: B=[b zeros; zeros eye], so the inverse can be computed
> as [inv(b) zeros; zeros eye] and it works ok. However inv(B) sometimes
> gives non-zeros on the upper right block!. So: by fail I mean incorrect
> results, and in that case the output is something like:
> sizeb = 19
> rankb = 19
> diffinvs = 32.430
> ans = 769.02
> ans = 1.1160e+06
> ans = 1.0000
> ans = 1.0000
> diffinvs_ = 32.430
> ans = 617.64
> ans = 28.923
> ans = 1.0000
> ans = 1.0000
> I tried Dmitri's suggestion:
> LD_PRELOAD=/usr/lib/x86_64-linux-gnu/blas/libblas.so.3.9.0 octave-cli
> chkBlockedInverse.m
> It still fails, but then I tried to rule out multithreading issues and ran:
> OMP_NUM_THREADS=1 octave-cli chkBlockedInverse.m
> And the results were:
> sizeb = 19
> rankb = 19
> diffinvs = 2.6377e-17
> ans = 1.0000
> ans = 1.0000
> ans = 1.0000
> ans = 1.0000
> diffinvs_ = 2.6377e-17
> ans = 5.4962
> ans = 5.5663
> ans = 1.0000
> ans = 1.0000
> So: the blocked matrix: [b zeros; zeros eye] is correctly inverted with
> one thread, the other: [eye zeros; zeros, b] seems to have some problems
> with precision, but the main issue seems to be in the multithreading
> implementation!
> Enzo
>
> On Sun, Dec 4, 2022 at 6:24 PM Dmitri A. Sergatskov <
> [email protected]> wrote:
>
>>
>>
>> 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.
>> --
>>
>>>
>>>
>>> ----------
>>> We are transitioning to a web based forum
>>> for community help discussions at
>>> https://octave.discourse.group/c/help
>>>
>>
>
> --
> Enzo A. Dari
> Profesor Titular
> Instituto Balseiro <http://www.ib.edu.ar/>
>


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


----------
We are transitioning to a web based forum
for community help discussions at
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