[Octave-bug-tracker] [bug #53390] lu factorization of large sparse matrices often fails

[Marco Caliari]

Follow-up Comment #11, bug #53390 (project octave):

@Rik: this bug has always been in octave and it is due, in my opinion, to a
misleading documentation in umfpack (the author told me he will add a
clarifying note to the documentation). If it came up only now, it is because
people eihter do not use lu of sparse matrices or use it in the right way
([L,U,P,Q] = lu (S), maybe after noting that otherwise it fails). The proposal
in comment #9 will take some time and it is not feasible for 4.4.0. What about
adding sentence in the documentation? Something like


When called with two or three output arguments and a sparse input
matrix, 'lu' does not attempt to perform sparsity preserving column
permutations.  Called with a fourth output argument, the sparsity preserving
column transformation Q is returned, such that 'P * A * Q = L * U'. This is
the preferred way to call lu with sparse input matrices.


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