Centre of matrix , order ( n / 2 ) * ( n / 2 )
for i in range ( n / 4 , 3 * ( n / 4 ) ) : NEW_LINE INDENT for j in range ( n / 4 , 3 * ( n / 4 ) ) : NEW_LINE INDENT arr [ i ] [ j ] = ( n * n + 1 ) - arr [ i ] [ j ] ; NEW_LINE DEDENT DEDENT