text: Centre of Matrix ( order ( n / 2 ) * ( n / 2 ) )
code: for ( i = parseInt ( n / 4 ) ; i < 3 * parseInt ( n / 4 ) ; i ++ ) for ( j = parseInt ( n / 4 ) ; j < 3 * parseInt ( n / 4 ) ; j ++ ) arr [ i ] [ j ] = ( n * n + 1 ) - arr [ i ] [ j ] ;