docs: boolean isVertex(double x, double y)
      {
          int cnt = points.numRows;
          double[] d = points.data;
          for (int ii=0;ii<cnt;ii++)
          {
              if (x == d[2*ii] && y== d[2*ii+1])
              {
                  return true;
              }
          }
          return false;
      }