#http://xuxzmail.blog.163.com/blog/static/25131916201232494954783/
#狗鞍面的方程为：z=x*y^3-y*x^3。这是一个4次曲面。
vertices = dimension1:320 dimension2:320
x = from (-2) to (2) dimension1
z = from (-2) to (2) dimension2
y = x*(z^3)-z*(x^3)
