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[Octave-bug-tracker] [bug #58944] [z, r, p]=qr(a, b) unexpectedly return
From: |
Rik |
Subject: |
[Octave-bug-tracker] [bug #58944] [z, r, p]=qr(a, b) unexpectedly returns z as q instead of q' * b |
Date: |
Thu, 13 Aug 2020 17:38:32 -0400 (EDT) |
User-agent: |
Mozilla/5.0 (Windows NT 10.0; WOW64; Trident/7.0; rv:11.0) like Gecko |
Update of bug #58944 (project octave):
Status: None => Need Info
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Follow-up Comment #1:
This may not be implemented in Octave. Looking at the documentation, the
calling forms are:
-- [Q, R] = qr (A)
-- [Q, R, P] = qr (A) # non-sparse A
-- X = qr (A) # non-sparse A
-- R = qr (A) # sparse A
-- [C, R] = qr (A, B)
-- [...] = qr (..., 0)
-- [...] = qr (..., "vector")
-- [...] = qr (..., "matrix")
There is a three-output form for a single input matrix A, but there is no
listing for a three-output form with 2 inputs. In the main body of the
documentation there is also no discussion of a form such as
[C, R, P] = qr (A, B)
It gets weirder. Matlab won't accept
[z,r,p] = qr (a,b);
and complains that the matrices must be sparse. If I do that with
[z,r,p] = qr (sparse(a),sparse(b));
then it works and returns a 3x1 vector.
However, Octave goes the other way. it will accept full matrices with a
permutation output, but not sparse ones:
[z,r,p] = qr(sparse(a),sparse(b));
error: qr: Permutation output is not supported for sparse input
I think we need to decide what should happen and then go implement that.
Should the [z,r,p] form be allowed with full matrices? Should the [z,r,p] =
qr (a,b) form work with sparse matrices?
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