bugGNU Octave - Bugs: bug #40305, real (sparse (2i)) creates bad...


bug #40305: real (sparse (2i)) creates bad internally formatted sparse matrix

Submitter:  Rik <rik5>
Submitted:  Fri 18 Oct 2013 05:48:45 PM UTC
Category:  Interpreter Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Segfault, Bus Error, etc.
Status:  Fixed Assigned to:  dbateman
Originator Name:  Open/Closed:  * Closed
Release:  * dev Operating System:  * GNU/Linux
Fixed Release:  None Planned Release:  None
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Fri 18 Oct 2013 10:48:37 PM UTC, comment #2: 

I backed the temporary fix out 12 minutes after you checked in your fix.

Rik <rik5>
Project Administrator
Fri 18 Oct 2013 09:18:28 PM UTC, comment #1: 

I'm surprised this bug was there since at least 2005 without being seen and fixed as the fix is trivial. See the changeset


Rik, should you backout the changeset 1d41b1910531 as casting a sparse matrix as full isn't really that great an idea as the memory requirement and performance might be significantly degraded.


David Bateman <dbateman>
Project Member
Fri 18 Oct 2013 05:48:45 PM UTC, original submission:  

I just tracked down a segfault in Octave to incorrect behavior of real() for sparse matrices.

Check out the following:

debug> x = sparse (2i)
x = Compressed Column Sparse (rows = 1, cols = 1, nnz = 1 [100%])

  (1, 1) ->  0 + 2i
debug> typeinfo (x)
ans = sparse complex matrix
debug> xr = real (x)
xr = Compressed Column Sparse (rows = 1, cols = 1, nnz = 1 [100%])

  (1, 1) -> 0
debug> typeinfo (xr)
ans = sparse matrix
debug> nnz (xr)
ans =  1

The problem is that the internal format seems to have become corrupted after the call to real which changed a non-zero entry to a zero entry.  nnz() should return 0 after the call to real().

If you try to use this bad matrix in further calculations it can lead to a segfault.  Example:

complex (xr, sparse (1))

Rik <rik5>
Project Administrator


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    Follow 3 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2013-10-18 dbateman StatusNone Fixed
        Assigned toNone dbateman
        Open/ClosedOpen Closed

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