function [ row, col, b ] = r8gb_to_r8sp ( m, n, ml, mu, a, nz_num )
%*****************************************************************************80
%
%% R8GB_TO_R8SP copies a R8GB matrix to a R8SP matrix.
%
% Discussion:
%
% The R8GB storage format is for an M by N banded matrix, with lower
% bandwidth ML and upper bandwidth MU. Storage includes room for ML
% extra superdiagonals, which may be required to store nonzero entries
% generated during Gaussian elimination.
%
% The original M by N matrix is "collapsed" downward, so that diagonals
% become rows of the storage array, while columns are preserved. The
% collapsed array is logically 2*ML+MU+1 by N.
%
% LINPACK and LAPACK band storage requires that an extra ML
% superdiagonals be supplied to allow for fillin during Gauss
% elimination. Even though a band matrix is described as
% having an upper bandwidth of MU, it effectively has an
% upper bandwidth of MU+ML. This routine will copy nonzero
% values it finds in these extra bands, so that both unfactored
% and factored matrices can be handled.
%
% The R8SP storage format stores the row, column and value of each nonzero
% entry of a sparse matrix.
%
% It is possible that a pair of indices (I,J) may occur more than
% once. Presumably, in this case, the intent is that the actual value
% of A(I,J) is the sum of all such entries. This is not a good thing
% to do, but I seem to have come across this in MATLAB.
%
% The R8SP format is used by CSPARSE ("sparse triplet"), SLAP
% ("nonsymmetric SLAP triad"), by MATLAB, and by SPARSEKIT ("COO" format).
%
% Licensing:
%
% This code is distributed under the GNU LGPL license.
%
% Modified:
%
% 14 September 2006
%
% Author:
%
% John Burkardt
%
% Parameters:
%
% Input, integer M, the number of rows of the matrices.
% M must be positive.
%
% Input, integer N, the number of columns of the matrices.
% N must be positive.
%
% Input, integer ML, MU, the lower and upper bandwidths of A1.
% ML and MU must be nonnegative, and no greater than min(M,N)-1.
%
% Input, real A(2*ML+MU+1,N), the R8GB matrix.
%
% Input, integer NZ_NUM, the number of nonzero entries in A.
% This number can be obtained by calling R8GB_NZ_NUM.
%
% Output, integer ROW(NZ_NUM), the row indices.
%
% Output, integer COL(NZ_NUM), the column indices.
%
% Output, real B(NZ_NUM), the R8SP matrix.
%
nz = 0;
for i = 1 : m
jlo = max ( 1, i - ml );
jhi = min ( n, i + mu + ml );
for j = jlo : jhi
if ( a(ml+mu+1+i-j,j) == 0.0 )
continue;
end
if ( nz_num <= nz )
fprintf ( 1, '\n' );
fprintf ( 1, 'R8GB_TO_R8SP - Fatal error!\n' );
fprintf ( 1, ' NZ_NUM = %d\n', nz_num );
fprintf ( 1, ' But the matrix has more nonzeros than that!\n' );
error ( 'R8GB_TO_DS3 - Fatal error!' );
end
nz = nz + 1;
row(nz) = i;
col(nz) = j;
b(nz) = a(ml+mu+1+i-j,j);
end
end
if ( nz < nz_num )
fprintf ( 1, '\n' );
fprintf ( 1, 'R8GB_TO_R8SP - Warning!\n' );
fprintf ( 1, ' NZ_NUM = %d\n', nz_num );
fprintf ( 1, ' But the number of nonzeros is %d\n', nz );
end
return
end