code: public void setFlipY(double y0, double y1) {
  		xx = 1;
  		xy = 0;
  		xd = 0;
  		yx = 0;
  		yy = -1;
  		yd = y0 + y1;
  	}
docs: Sets the transformation to be a flip around the Y axis. Flips the Y
  coordinates so that the y0 becomes y1 and vice verse.
  
  @param y0
  The Y coordinate to flip.
  @param y1
  The Y coordinate to flip to.