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[Octave-bug-tracker] [bug #58944] [z, r, p]=qr(a, b) unexpectedly return

From: Markus Mützel
Subject: [Octave-bug-tracker] [bug #58944] [z, r, p]=qr(a, b) unexpectedly returns z as q instead of q' * b
Date: Wed, 13 Jan 2021 09:40:36 -0500 (EST)
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.141 Safari/537.36 Edg/87.0.664.75 
Follow-up Comment #3, bug #58944 (project octave):

I tried the following with Octave at hg id 512591ccb174 (i.e., after the
changes for bug #57033 ):

>> A = rand(3,2);
>> B = rand(3,1);
>> [C, R, E] = qr (sparse(A), sparse(B));
>> X = E*(R\C);
>> A*X
ans =

   0.1617
   0.2306
   0.2725

>> B
B =

   0.802331
   0.021141
   0.069525


It looks like the identity described in comment #2 doesn't hold with our
current implementation.

Is that a problem?

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  <https://savannah.gnu.org/bugs/?58944>

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