(Comp.sources.hp48)
Item: 115 by eldorado@ecn.purdue.edu [Dave Jansen]
  Subj: 3d plot
  Date: Mon Jun 01 1992

Here is a 3 dimensional surface graphing program for the HP48SX.

Some features are:
1.  It doesn't go belly up if it encounters a divide by zero or
                    undefined result.
2.  It allows the domains of the XY plane to be defined to any value
                    (although it centers the plot on the origin).
3.  The equation is entered in X, Y, Z format not parametric form.
4.  It creates a matrix of the topology of the surface which is useful for
                    locating actual values of a max or min.

It is controlled by its own plot parameters which are stored in SPAR.  SPAR
is defined as a list with the following elements:
{ lower X limit; upper X limit; X increment; lower Y limit; upper Y limit;
          Y increment; angle of X with horizontal; angle of Y with horizontal;
          flag signalling to plot a plane at Z; value of Z to plot plane;
          X expansion factor; Y expansion factor }

The upper and lower X limit is the domain in the X coordinate.
Likewise for the upper and lower Y limit.

The X and Y increments set how close together the points will be.

The angles allow the XY plane to change shape for better viewing.  If they
are changed by the same amount for consecutive plots, the graph will seem 
to rotate.  A type of rotation by 90 degrees can be done using the Translate
command on the variable TOPO.  The Translate command is found in the Matrix
directory.

The flag determining whether an XY plane should be plotted can have the
values -1, 0, 1.  0 designates no plane plotted.  1 designates the surface
will be plotted on top of the plane.  -1 draws the plane above the surface.

Z is the value one the Z axis (the altitude) at which the XY plane will
be plotted.

The X and Y expansion factors scale the graph on the HP screen.

Directions

1.  Enter your equation and store it in varible EQ
2.  Press the SFACE menu key
3.  Wait for the screen to draw and then press a key to end
4.  If you wish to change one of the parameters in SPAR, do so and then
    choose TRACE since the topology of the EQ is known.  This means that
    recalculation is not needed to review the graph.
5.  The topology and the actual graph are saved when done.

Enjoy.  Send comments, questions, complaints to:

Dave Jansen             |  INTERNET:  eldorado@en.ecn.purdue.edu
Electrical Engineering  |  BITNET:    eldorado%ea.ecn.purdue.edu@purccvm
Purdue University       |  UUCP:     {purdue,pur-ee}!en.ecn.purdue.edu!eldorado