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function [Ap, Ai, Ax] = sparse2csr(A, is_one_based_in)
%
% [Ap, Ai, Ax] = sparse2csr(A, [is_one_based])
%
% convert matlab sparse matrix to
% Compressed sparse row format
%
is_one_based = 0;
if (nargin >= 2),
is_one_based = is_one_based_in;
end;
is_zero_based = ~is_one_based;
nrow = size(A,1);
ncol = size(A,2);
nnzA = nnz(A);
Ap = zeros( 1,nrow+1);
Ai = zeros( 1,nnzA);
Ax = zeros( 1,nnzA);
% -----------------
% coordinate format
% -----------------
[ii,jj,aa] = find(A);
% ---------------------------
% sort to group rows together
% ---------------------------
[dummy, iperm] = sort( jj + (ii-1) * ncol);
clear dummy;
ii = ii(iperm);
jj = jj(iperm);
aa = aa(iperm);
% -------------------------
% compute non-zeros per row
% -------------------------
nz_per_row = sum( A ~= 0, 2);
% -------------------------
% setup Ap(:) pointer array
% -------------------------
Ap(1) = 1;
Ap(2:(nrow+1)) = 1+cumsum( nz_per_row(1:nrow) );
% ------------------------------------------
% fill Ai(:) column indices and Ax(:) values
% ------------------------------------------
istart=1;
for irow=1:nrow,
if (nz_per_row(irow) >= 1),
iend = istart + nz_per_row(irow)-1;
is_same_row = all( ii(istart:iend) == irow );
if (~is_same_row),
error(sprintf('sparse2csr: irow=%g,istart=%g,iend=%g', ...
irow, istart, iend ));
end;
Ai(istart:iend) = jj(istart:iend);
Ax(istart:iend) = aa(istart:iend);
istart = iend + 1;
end;
end;
if (is_zero_based),
Ap = Ap-1;
Ai = Ai-1;
end;
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