$rows = n;
$cols = m;
$rowstep = i;
$colstep = j;
$num_row_subs = $rows/$rowstep;
$num_col_subs = $cols/$colstep;

for $r (0 .. $num_row_subs-1) {
	for $c (0 .. $num_col_subs-1) {
		for $sub_row (0 .. $rowstep-1) {
			for $sub_col (0 .. $colstep-1) {
				$row = $r*$rowstep+$sub_row;
				$col = $c*$colstep+$sub_col;
				print "[$r*$rowstep+$sub_row = $row][$c*$colstep+$sub_col = $col]<br>\n";
			}
		}
	}
}