Polyfit crashes octave 3.0.0

[Ben Abbott]

On Apr 10, 2008, at 8:02 AM, Sergei Steshenko wrote:
>
> --- Ben Abbott <bpabbott at mac.com> wrote:
>
>>
>> On Apr 10, 2008, at 3:19 AM, Jaroslaw Pychowski wrote:
>>> --------
>>> Bug report for Octave 3.0.0 configured for i486-pc-linux-gnu
>>>
>>> Description:
>>> -----------
>>>
>>> Function polyfit causes segmentation fault.
>>> 51 is minimal affected value of n (see code below)
>>> Messages emitted before segmentation fault:
>>> octave:5> wn=polyfit(x,y,n);
>>> warning: matrix singular to machine precision, rcond = 1.83429e-25
>>> warning: attempting to find minimum norm solution
>>> panic: Segmentation fault -- stopping myself...
>>> attempting to save variables to `octave-core'...
>>> save to `octave-core' complete
>>> Segmentation fault
>>>
>>> Repeat-By:
>>> ---------
>>> n=51
>>> step=2/n;
>>> x=-1:step:1;
>>> y=abs(5*x);
>>> wn=polyfit(x,y,n);
>>
>> I'm replying to report the results on Mac OSX.
>>
>> On Mac OSX 10.5.2 with gfortran 4.3 and Apple's vecLib the results  
>> for
>> each of the mercurial branches are below.
>>
>> branch: release-3-0-x
>>
>> octave:6> n=51;
>> octave:7> step=2/n;
>> octave:8> x=-1:step:1;
>> octave:9> y=abs(5*x);
>> octave:10> wn=polyfit(x,y,n);
>> warning: matrix singular to machine precision, rcond = 1.83428e-25
>> warning: attempting to find minimum norm solution
>> warning: dgelsd: rank deficient 52x52 matrix, rank = 42
>>
>> branch: default
>>
>> octave:5> n=51;
>> octave:6> step=2/n;
>> octave:7> x=-1:step:1;
>> octave:8> y=abs(5*x);
>> octave:9> wn=polyfit(x,y,n);
>> octave:10>
>>
>> The default branch uses QR decomposition. The 3-0-x release uses left
>> divide, but neither gives a seg-fault for me.
>>
>> Ben
>>
>> _______________________________________________
>> Bug-octave mailing list
>> Bug-octave at octave.org
>> https://www.cae.wisc.edu/mailman/listinfo/bug-octave
>>
>
> Segfaults in my case:
>
> "
> GNU Octave, version 3.0.0
> Copyright (C) 2007 John W. Eaton and others.
> This is free software; see the source code for copying conditions.
> There is ABSOLUTELY NO WARRANTY; not even for MERCHANTIBILITY or
> FITNESS FOR A PARTICULAR PURPOSE.  For details, type `warranty'.
>
> Octave was configured for "i686-pc-linux-gnu".
>
> Additional information about Octave is available at http://www.octave.org 
> .
>
> Please contribute if you find this software useful.
> For more information, visit http://www.octave.org/help-wanted.html
>
> Report bugs to <bug at octave.org> (but first, please read
> http://www.octave.org/bugs.html to learn how to write a helpful  
> report).
>
> For information about changes from previous versions, type `news'.
>
> octave:1> n=51
> n =  51
> octave:2> step=2/n;
> octave:3> x=-1:step:1;
> octave:4> y=abs(5*x);
> octave:5> wn=polyfit(x,y,n);
> warning: matrix singular to machine precision, rcond = 1.83429e-25
> warning: attempting to find minimum norm solution
> panic: Segmentation fault -- stopping myself...
> attempting to save variables to `octave-core'...
> save to `octave-core' complete
> ".
>
> Built by myself 'octave', built built by myself gcc-4.2.3, but other  
> than that SUSE 10.2
>
> Regards,
>  Sergei.

Sergei,

Did you build from the original 3.0.0 release, or from the mercurial  
sources. ... and did you build using gfortran, if so what version?

I ask because, jwe had made some recent modifications that resolved  
similar problem on Mac OSX when Octave was built with gfortran 4.3 and  
used Apples lapack/blas ... actually I shouldn't say "problem" because  
as one was resolved, yet another was revealed.

In any event, my problem(s) were resolved by John in Mar 19. See the  
thread below.

	http://www.nabble.com/failed-build-with-current-mercurial-sources-tt15896284.html#a15944481

It may be that this particular problem is related.

Ben