[Octave-bug-tracker] [bug #41116] Incorrect result for sparse LU factorization

[Marco Caliari]

Follow-up Comment #8, bug #41116 (project octave):

Dear Michael,


[LL2,UU2]=lu(full(x));


makes no column permutation: in fact LL2*UU2=x, without any Q matrix.
With the workaround I suggested, I get from


[LL,UU]=lu(x);
+verbatim-

exactly the same (correct) factorization, that is no column permutation in the
final result. It seems to me that the column reordering we see between the
symbolic and the numerical factorization in UMFPACK is a sort of "inner"
reordering that we have to take into account, but without a real column
permutation (that is Q different from identity) in the result.

Marco

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