[Octave-bug-tracker] [bug #47415] out of memory negating a permutation matrix

[Rik]

Follow-up Comment #28, bug #47415 (project octave):

I think Carlo is on to something here.  At least when the input matrix is
sparse, the output matrix P should also be sparse (or behave like a sparse
matrix) for compatibility.

According to Octave's documentation,


If A is full subroutines from LAPACK are used and if A is sparse then UMFPACK
is used.


So there may still be a compatibility issue if Matlab returns a full
permutation matrix P when the input is a full matrix.  What does Matlab do for
this


A = sprandn (100, 100, .02);
Af = full (A);
[L, U, P, Q, R] = lu (Af);
issparse (P)


Also, if I understand things correctly it shouldn't return the Q and R values
as those are only for sparse matrices.



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