code: public void setVertex(int i, double x, double y) {
          this.x.set(i, x);
          this.y.set(i, y);
          this.z.set(i, 0d);
          calcG();
      }
docs: Sets the coordinates of the point.
  
  @param i The index number of the point.
  @param x The x-coordinate of the point.
  @param y The y-coordinate of the point.