3D Plotter for mathematical functions

Do you like the shaded three-dimensional body shown in the main menu page below with the wavy surface? If you agree, you find the accompanying program for computing any mathematical continuous function of class

z = f(x,y)

to such a body. This program is available both for GW-BASIC (up to EGA graphic modes only) and QuickBASIC (VGA video modes) well as. Each of these both .ZIP files contains a few of versions for different graphic modes. In the GW-BASIC version you have to insert your desired function on the top in line 140:

140 DEF FN F!(X!, Y!)=X!^2!+Y!^2!

This example will arise e.g. a paraboloid according to the equation z=x²+y². At the QuickBASIC version you have to place your wished function in the specially designed FUNCTION procedure FvonXundY, e.g. with the example above:

FUNCTION FvonXundY! (x!, y!) STATIC
  ' Hier muss die eigentliche Funktion definiert werden
  FvonXundY! = x! ^ 2! + y! ^ 2!
END FUNCTION

In further you can set freely the section cuboid, angle of vision and drawing precision so you will receive any results like in the main menu page below:

Screen shot: Three-dimensional body with waved, checked surface. Bigger
extent of 22¾ KB

For helping while optimising the section cuboid this programs outputs the lowest and the highest z value on the screen while finishing. I hope you enjoy this program! Incidental note: If you find one or more functions with a nice result you should tell them by e-mail to me, please. Thanks very much!