[Octave-bug-tracker] [bug #65170] [octave forge] (statistics) Failing BIST in fitcknn

[Rafael Laboissière]

URL:
  <https://savannah.gnu.org/bugs/?65170>

                 Summary: [octave forge] (statistics) Failing BIST in fitcknn
                   Group: GNU Octave
               Submitter: rlaboiss
               Submitted: Tue 16 Jan 2024 05:07:27 PM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Unexpected Error or Warning
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: other
         Discussion Lock: Any
        Operating System: GNU/Linux
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


-------------------------------------------------------
Date: Tue 16 Jan 2024 05:07:27 PM UTC By: Rafael Laboissière <rlaboiss>
One of the BISTs of function fitcknn of the statistics package, version 1.6.1,
is failing:


octave:1> pkg load statistics
octave:2> test fitcknn
***** test
 x = [1, 2, 3; 4, 5, 6; 7, 8, 9; 3, 2, 1];
 y = ["a"; "a"; "b"; "b"];
 C = cov (x);
 a = fitcknn (x, y, "Cov" , C, "distance", "mahalanobis");
 assert (class (a), "ClassificationKNN");
 assert ({a.DistParameter}, {C})
 assert ({a.NSMethod, a.Distance}, {"exhaustive", "mahalanobis"})
 assert ({a.BucketSize}, {50})
!!!!! test failed
ClassificationKNN: Cov must be a symmetric positive definite matrix.


According to the documentation, the argument "Cov" must be a positive definite
matrix. Now, in the BIST above, the C matrix is not positive definite.
Indeed:


octave:3> x = [1, 2, 3; 4, 5, 6; 7, 8, 9; 3, 2, 1];
octave:4> C = cov (x);
octave:5> [~, p] = chol (C)
p = 3










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