//saddle surface(Hyperbolic paraboloid)function, used to calculate the delay time of each cube
//z = 1.0 + y*y/a/a - x*x/b/b
//with our selection of parameters(a and b), this value for any cube is between 0.0 and 2.0
//saddle surface(Hyperbolic paraboloid)function, used to calculate the delay time of each cube
//z = 1.0 + y*y/a/a - x*x/b/b
//with our selection of parameters(a and b), this value for any cube is between 0.0 and 2.0