This script draws a 3D surface plot with hidden-line removal.
The expression to plot is defined in a python function which takes 2 arguments (x,y) and returns z.
Plotting is performed by python function surf() which takes arguments telling it which function to plot and the ranges on x,y and z axis. An optional text string can be added to the plot.
The script uses a function which extends the functionality of the kandinsky module:
connect draws a line between two arbitrary points
connect(x1,y1,x2,y2,co="black")
The script uses only the math and kandinsky libraries.