Yes, it is possible to use idx to reduce the number of additions.
matrix(matrix<thresh) = 0 ;
idx = find(matrix~=0);
[idxr, idxc] = ind2sub(size(matrix), idx);
numcol = size(matrix,2);
while condition is true
matrix(idx) = matrix(idx).*another matrix(idx) %matrix is sparse and has lot of zeros ;numel(matrix) = 1000000
for col = 1 : num2col
matched_rows = idxr(idxc==col);
new_matrix(a,col) = b * sum(matrix(matched_rows, col));
end
end
I would be surprised if this is more efficient, but it is possible . It would probably be more efficient to loop calculating the column-wise indices into a cell array and indexing into that.
