[Octave-bug-tracker] [bug #61246] matrix inversions give wrong results (inv, lu, mldivide)

[Markus Mützel]

Follow-up Comment #5, bug #61246 (project octave):

For me on Windows 10 with Octave 6.3.0 (32bit) using reference BLAS:

>> version -blas
ans = unknown or reference BLAS
>> n = 7;
>> randn('seed',1);
>> a = randn(n);
>> x = (1:n)';
>> b = a * x;
>> r = x - a \ b
r =

   1.7764e-15
   3.5527e-15
  -1.3323e-15
  -3.5527e-15
  -8.8818e-16
   2.6645e-15
  -2.6645e-15


And the same with OpenBLAS:

>> version -blas
ans = OpenBLAS (config: OpenBLAS 0.3.13 NO_LAPACK NO_LAPACKE DYNAMIC_ARCH
NO_AFFINITY Nehalem MAX_THREADS=24)
>> n = 7;
>> randn('seed',1);
>> a = randn(n);
>> x = (1:n)';
>> b = a * x;
>> r = x - a \ b
r =

   4.6629e-15
   1.0214e-14
   2.6645e-15
  -7.9936e-15
  -1.7764e-15
   1.7764e-15
  -5.3291e-15


I don't see the large deviations you are using.

My CPU:

>> system('wmic CPU GET Name')
Name
Intel(R) Core(TM) i5-4690 CPU @ 3.50GHz



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