This function subtracts B [ ] [ ] from A [ ] [ ] , and stores the result in C [ ] [ ]
function subtract ( A , B , C ) { var i , j ; for ( i = 0 ; i < N ; i ++ ) for ( j = 0 ; j < N ; j ++ ) C [ i ] [ j ] = A [ i ] [ j ] - B [ i ] [ j ] ; }