code: public static void flip( int []a , int N ) {
  		int H = N/2;
  
  		for (int i = 1; i <= H; i++) {
  			int j = N-i;
  			int tmp = a[i];
  			a[i] = a[j];
  			a[j] = tmp;
  		}
  	}
docs: TODO move into ddogleg? primitive flip  <--- I think this is specific to polygons