#### Example.

Input:

plot3d(x*y,x,y)

Output:

To draw a parameterized surface:

- plot3d takes one mandatory argument and two optional arguments:
  - funcs, a list of three functions or three expressions involving two variables.
  - u and v, the names of the variable in the expression (if funcs is a list of expressions), which can also specify a range of values for each variable.

    If funcs is a list of functions, this argument is optional, and are the ranges a..b for the variables.

    If the ranges are not given, the default values are taken from the graph configuration (see Section 2.5.8).

- plot3d(funcs,u,v) draws the surface.

#### Examples.

- Input:
  plot3d([v*cos(u),v*sin(u),v],u,v)
  Output:
- Input:
  plot3d([v*cos(u),v*sin(u),v],u=0..pi,v=0..3)
  Output: