[Octave-bug-tracker] [bug #57460] Tolerance exceeded in test for "svds" on Windows

[Markus Mützel]

URL:
  <https://savannah.gnu.org/bugs/?57460>

                 Summary: Tolerance exceeded in test for "svds" on Windows
                 Project: GNU Octave
            Submitted by: mmuetzel
            Submitted on: Sun 22 Dec 2019 11:10:10 AM CET
                Category: Test Suite
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Inaccurate Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Microsoft Windows

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Details:

Running the test suite on Windows with Octave hg id 1a75fca6ad5d and MXE
Octave hg id 5a6318b5b71d, I see the following error for svds.m:

>>>>> processing
D:\Repositories\Octave\test\octave-2019-12-22-10-10-w64_clean\octave-2019-12-22-10-10-w64\mingw64\share\octave\6.0.0\m\sparse\svds.m
***** testif HAVE_ARPACK
 [u2,s2,v2,flag] = svds (A,k);
 s2 = diag (s2);
 assert (flag, ! 1);
 tol = 10 * eps() * norm(s2, 1);
 assert (s2, s(end:-1:end-k+1), tol);
!!!!! test failed
ASSERT errors for:  assert (s2,s (end:-1:end - k + 1),tol)

  Location  |  Observed  |  Expected  |  Reason
    (4)        41.9848      41.9848      Abs err 7.6739e-13 exceeds tol
6.5244e-13 by 1e-13


The shared variables used for this test are:

n = 100;
k = 7;
A = sparse
([3:n,1:n,1:(n-2)],[1:(n-2),1:n,3:n],[ones(1,n-2),0.4*n*ones(1,n),ones(1,n-2)]);
[u,s,v] = svd (full (A));
s = diag (s);
[~, idx] = sort (abs (s));
s = s(idx);


Maybe it is good enough to just increase the tolerance.
But it would be better if someone more experienced in numerical mathematics
could comment.




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