### 6.11.2  3D parametric surface : plotparam paramplot DrawParm

plotparam takes two main arguments, a list of three expressions of two variables and the list of these variable names where each variable name may be replaced by variable=interval to specify the range of the parameters. It accepts an optional argument to specify the discretization steps of the parameters u and v with ustep=... and vstep=....
plotparam([f(u,v),g(u,v),h(u,v)],[u,v]) draws the surface defined by the first argument : x=f(u,v),y=g(u,v),z=h(u,v), where u and v ranges default to the graphic configuration.
Input :

plotparam([v*cos(u),v*sin(u),v],[u,v])

Output :

The cone x=v*cos(u),y=v*sin(u),z=v

To specify the range of each parameters, replace each variable by an equation variable=range, like this:

plotparam([v*cos(u),v*sin(u),v],[u=0..pi,v=0..3])

Output :

A portion of the cone x=v*cos(u),y=v*sin(u),z=v

Input :

plotparam([v*cos(u),v*sin(u),v],[u=0..pi,v=0..3],ustep=0.5,vstep=0.5)

Output :

A portion of the cone x=v*cos(u),y=v*sin(u),z=v