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[Octave-bug-tracker] [bug #51950] Segfault during a sparse QR factorizat


From: Marco Caliari
Subject: [Octave-bug-tracker] [bug #51950] Segfault during a sparse QR factorization
Date: Wed, 6 Sep 2017 12:13:25 -0400 (EDT)
User-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:55.0) Gecko/20100101 Firefox/55.0

Follow-up Comment #3, bug #51950 (project octave):

I confirm the problem in 4.2.1. It seems to me that in order to trigger the
bug you need r rectangular and with some zeros on the diagonal. I have no
problem with


A = sprandn(5, 6, 1);[q r] = qr(A);[q r] = qr(r);


(no zeros on the diagonal of r) or


A = sprandn(5, 5, 0.1);[q r] = qr(A);[q r] = qr(r);


(r is square). But, it is strange to me that I have no problem with


r = sprandn(5, 6, 0.1);r = triu(r);[q r] = qr(r);


It seems that r has to be the result of a qr factorization and not a simple
upper triangular rectangular matrix with some zeros on the diagonal. Strange.

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