generates a cell list of variational parameters for a sparse array. Useful for doing gradient descent on said array.

cmtxvars.cpp

#include <octave/oct.h>
#include <octave/Cell.h>

// SPECIAL FUNCTION THAT CONVERTS A SPARSE MATRIX 
// TO A MATRIX THAT LISTS (ROW COLUMN) OF THE FILLED VALUES

DEFUN_DLD (cmtxvars, args,  nargout, "creates a cell matrix of variations on a sparse matrix")
{
  int nargin = args.length();
  if (nargin < 1)
    print_usage ();  //make sure we actually sent one value in.
  else
  {
  	//pull the sparse matrix from the argument.
  	SparseMatrix sm = args(0).sparse_matrix_value ();
    //pull the amount we're going to do variation by from the argument.
    double delta = (nargin > 1) ? args(1).float_value() : 0.01;

  	//count how many elements we have, this should also be
  	//the length of ri array
    int count = sm.nelem();
    //save the original dimensions vector.
    dim_vector smsize(sm.dim1(), sm.dim2());

    //cursor will be used to iterate over ci array.
    int cursor = 0;

    //allocate a new cell array to store our variational matrices.
    dim_vector cmsize(count);
    Cell c(cmsize);

    //iterating over the length of the sparse matrix:
    for (int index = 0; index < count; index++)
    {
       //create a new sparse matrix.
       SparseMatrix tm(sm);
       //add the variational parameter into the matrix.
       tm.data()[index] += delta;
       //store it into the cell array
       c(index) = tm;
    }
   
    //return the cell array.
    return octave_value (c);
  }
  return octave_value_list ();
}