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

[Archisman Panigrahi]

URL:
  <https://savannah.gnu.org/bugs/?58926>

                 Summary: Octave gives wrong results with intel-mkl when
diagonalizing large matrices
                 Project: GNU Octave
            Submitted by: apandada1
            Submitted on: Mon 10 Aug 2020 06:01:06 AM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: 5.2.0
         Discussion Lock: Any
        Operating System: GNU/Linux

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Details:

I installed octave (5.2.0) and intel-mkl (2020.0.166) from the default
repositories of Ubuntu 20.04

When I try to diagonalize a large matrix, Octave gives wrong results with MKL
(it is much faster, though).

This is the code (https://pastebin.pl/view/611d6fe3) which gives wrong results
with MKL.

```
for a = 1:500
        for b = 1:500
                c(a,b) = sin(a + b^2);
        endfor
endfor
 
g = eig(c);
max(real(g))
```

The correct result is `ans = 16.915` (I checked this before installing
intel-mkl, and also in another Ubuntu 18.04 installation in the same computer,
where intel-mkl was not installed).

With MKL in Ubuntu 20.04, I get random numbers of order 10^5 - 10^6, which
change every time the code is run.

I don't know whether this is related to
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=921207





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File Attachments:


-------------------------------------------------------
Date: Mon 10 Aug 2020 06:01:06 AM UTC  Name: testmkl.m  Size: 96B   By:
apandada1
code which produces wrong results with MKL
<http://savannah.gnu.org/bugs/download.php?file_id=49648>

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