bugGNU Octave - Bugs: bug #55831, Incorrect sparse QR factorization


bug #55831: Incorrect sparse QR factorization

Submitter:  None
Submitted:  Tue 05 Mar 2019 07:37:57 AM UTC
Category:  Octave Function Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Incorrect Result
Status:  Duplicate Assigned to:  None
Originator Name:  Originator Email:  -email is unavailable-
Open/Closed:  * Closed Release:  * 5.1.0
Operating System:  * Any Fixed Release:  None
Planned Release:  None
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Wed 06 Mar 2019 08:03:46 PM UTC, comment #2: 

Yes, marking as a duplicate and closing report.

Rik <rik5>
Project Administrator
Wed 06 Mar 2019 02:41:02 PM UTC, comment #1: 

I think it is a duplicate (or related to) bug #51950.

Marco Caliari <caliari>
Project Member
Tue 05 Mar 2019 07:37:57 AM UTC, original submission:  

The following code:
[Q,R] = qr(sparse([1,0;0,0]));
Q = [-1 0
      0 0]

obviously Q is not unitary
it seems to me that each column with all zeros in a sparse input return a column with all zeros in the Q matrix

the size of Q is also incorrect when the input is sparse and an economy size factorization is requested. e.g.:
[Q,R] = qr(sparse(5,2),0);
outputs Q with size 5x5 rather than 5x2. Even though Q is 5x5, R is 2x2.

btw, is there a reason why Octave does not return a sparse Q like Matlab does when the input is sparse? I know Q is usually dense, but in some cases it may be sparse (e.g., economy factorization of a tall and sparse matrix). This could be useful to avoid running out of memory, for instance.



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    Follow 4 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2019-03-06 rik5 StatusNone Duplicate
        Open/ClosedOpen Closed
        Dependencies- Depends on bugs #51950
    2019-03-06 caliari Operating SystemMicrosoft Windows Any

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