[Octave-bug-tracker] [bug #51950] sparse qr may return a malformed sparse matrix R with out of bounds entries

[Rik]

Follow-up Comment #10, bug #51950 (project octave):

Unfortunately, it doesn't seem to be the sorting.  I commented out the sort
code and then re-ran the example


r =

Compressed Column Sparse (rows = 5, cols = 6, nnz = 6 [20%])

  (1, 1) -> -0.80000
  (2, 2) -> -1.4000
  (3, 3) -> -0
  (4, 4) -> -0
  (5, 5) -> -0
  (6, 6) ->  0.50000


So the extra zeros are not dropped, but the problem remains at location
(6,6).

Maybe we aren't calling QR correctly, or we've discovered some weird
longstanding bug in the library.  Someone who understands the CSPARSE library
needs to help out here.

The call is at line 208 of sparse_qr.cc


      BEGIN_INTERRUPT_IMMEDIATELY_IN_FOREIGN_CODE;
      S = CXSPARSE_DNAME (_sqr) (order, &A, 1);
      N = CXSPARSE_DNAME (_qr) (&A, S);
      END_INTERRUPT_IMMEDIATELY_IN_FOREIGN_CODE;



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