[Octave-bug-tracker] [bug #41116] Incorrect result for sparse LU factorization

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?41116>

                 Summary: Incorrect result for sparse LU factorization
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Mon 06 Jan 2014 02:33:23 AM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Michael C. Grant
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.8.0
        Operating System: Mac OS

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Details:


load lutest
[LL,UU]=lu(x);
[LL2,UU2]=lu(full(x));
LL*UU-x % this should be zero, but is not
LL2*UU2-x % this is zero
LL-LL2 % this is zero
UU-UU2 % this should be zero, but is not

Inspection reveals that the columns of UU remain un-permuted. But using the
three-argument version of LU does not seem to help:

[LL3,UU3,PP3]=lu(x);
LL3*UU3-PP3*x

PP3 is actually the identity matrix.
I have verified this both with a version of Octave 3.8 compiled with Homebrew,
and the prebuilt binaries from Octave Forge.



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File Attachments:


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Date: Mon 06 Jan 2014 02:33:23 AM UTC  Name: lutest  Size: 248B   By: None

<http://savannah.gnu.org/bugs/download.php?file_id=30199>

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