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

 
 

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

Submitted by:  Rik <rik5>
Submitted on:  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:  David Bateman <dbateman>
Originator Name:  Open/Closed:  Closed
Release:  dev Operating System:  GNU/Linux

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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

http://hg.savannah.gnu.org/hgweb/octave/rev/8031fc73f291

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

David Bateman <dbateman>
Project MemberIn charge of this item.
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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