Most of the same operators and functions on sparse matrices that are
available from the Octave are equally available with oct-files. 
The basic means of extracting a sparse matrix from an octave_value
and returning them as an octave_value, can be seen in the
following example.
     octave_value_list retval;
     
     SparseMatrix sm = args(0).sparse_matrix_value ();
     SparseComplexMatrix scm =
         args(1).sparse_complex_matrix_value ();
     SparseBoolMatrix sbm = args(2).sparse_bool_matrix_value ();
     ...
     retval(2) = sbm;
     retval(1) = scm;
     retval(0) = sm;
   The conversion to an octave-value is handled by the sparse
octave_value constructors, and so no special care is needed.