Re: libSVM support in Octave

[David Bateman]

Alois Schloegl wrote:
> This allows to use SVMTRAIN. However, at run-time the function 
> SVMPREDICT results in this error.
>
> error: octave_base_value::nzmax (): wrong type argument `matrix'
> panic: Segmentation fault -- stopping myself...
> attempting to save variables to `octave-core'...
> save to `octave-core' complete
> Segmentation fault
>
> After some debugging, the error massage is caused in svm_model_matlab.c 
> (line 6681) by this command
>    [num_samples] = mxGetNzmax(rhs[id]);
>  
> The segmentation fault occures only a few lines later, perhaps because 
> num_samples is -1.
>
> Again, I'd like asking you whether mxGetNzmax is implemented/supported, 
> or not.
>
>   
This is because the nzmax function is DLD-FUNCTIONS/sparse.cc was made a
method of the octave_value class. When it was a function it converted
matrices to sparse matrices prior to calling nzmax (or in fact nnz).
This feature wasn't kept when the code became an octave_value method...
The only logical way to treat this would be

octave_idx_type
octave_matrix::nnz (void) const
{
  return SparseMatrix (matrix).nnz ();
}

octave_idx_type
octave_matrix::nzmax (void) const
{
  return SparseMatrix (matrix).nzmax ();
}

and to the complex class

octave_idx_type
octave_complex_matrix::nnz (void) const
{
  return SparseComplexMatrix (matrix).nnz ();
}

octave_idx_type
octave_complex_matrix::nzmax (void) const
{
  return SparseComplexMatrix (matrix).nzmax ();
}

And similar to the boolean and scalar classes as well. I'm not sure
whether the integer classes should implement something similar of not,
though  nnz(uint8(eye(5)))  works correctly in matlab 2006a and so I
suspect the answer is we should.

That being the case, perhaps it would be better to have nnz and nzmax
methods in the Array<T> class and just call these.

D.


-- 
David Bateman                                address@hidden
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