Re: Importing a sparse matrix to Octave

[Carlo de Falco]

On 24 Jul 2009, at 14:06, Chong Yidong wrote:

> "John W. Eaton" <address@hidden> writes:
>
> >  # name: s
> >  # type: sparse complex matrix
> >  # nnz: 70
> >  # rows: 10
> >  # columns: 10
> >  1 1 (0,1.145193428282681)
> >  2 1 (0,0.5663270399606521)
> >  3 1 (0,0.007270909230606313)
> >  4 1 (0,0.1480797228543177)
> >  5 1 (0,0.2478795113138578)
> >  ...
> >
> > The first column is the row index, the second is the column index,  
> > and
> > the third is the corresponding value (real,complex).  The number of
> > elements must match the value of NNZ.  To load this file into Octave,
> > use the load command.
>
> Thanks.  However, this method doesn't seem to work properly:
>
> # name: s
> # type: sparse complex matrix
> # nnz: 3
> # rows: 10
> # columns: 10
> 1 1 (0,1.14)
> 3 6 (0,0.56)
> 6 2 (0.1,0.0)
>
> octave:1> load "foo.dat"
> octave:2> s
> s =
>
> Compressed Column Sparse (rows = 10, cols = 10, nnz = 3)
>
>  (1, 1) ->  0.00000 + 1.14000i
>  (3, 2) ->  0.00000 + 0.56000i
>  (6, 2) ->  0.10000 + 0.00000i
>
> The second line seems to be assigned to the wrong entry.  Is this a  
> bug?
> I'm using Octave 3.0.1, as distributed by Ubuntu.

If your code is free software you could also link it directly to  
octave-lib and let octave-lib handle the file format by doing  
something like:


--------------------------- BEGIN save_example.cc  
---------------------------
#include <octave/oct.h>
#include <octave/load-save.h>
#include <iostream>

extern bool save_ascii_data (std::ostream& os, const octave_value&  
val_arg,
                             const std::string& name, bool mark_as_global,
                             int precision);
int main (void) {
  SparseComplexMatrix M (10, 10, 3);
  M (0, 0) =   std::complex<double> (0, 1.14);
  M (2, 5) =   std::complex<double> (0, 0.56);
  M (5, 1) =   std::complex<double> (0.1, 0.0);

  const octave_value val (M);
  std::string name ("M");

  save_ascii_data   ( std::cout, val, name, 0, 10);

  return 0;
}
--------------------------- END save_example.cc  
---------------------------

mkoctfile --link-stand-alone save_example.cc -o save_example
./save_example > saved_matrix
octave -q

>> load saved_matrix
>> M
M =

Compressed Column Sparse (rows = 10, cols = 10, nnz = 3 [3%])

  (1, 1) ->  0.00000 + 1.14000i
  (6, 2) ->  0.10000 + 0.00000i
  (3, 6) ->  0.00000 + 0.56000i


HTH,
c.

P.S. sorry for my very bad c++ style...