Implicit function graph.  This program creates a graph of an implicit
function of X and Y.




Program:   IMPLGRAF
Author:    John P. Powers  (jpp@cpdvax.csc.ti.com)
Date:      January 7, 1993

This program graphs an implicit function of X and Y formulated as an
inequality.

Define equation variable FXY with the implicit function before
running this program.  FXY should contain an inequality using
variables X and Y.

Run program IMPLGRAF.  Depending on the complexity of the definition
of FXY, the graph will be completed in 3-1/2 minutes (or more).

Example:
   Graph the inequality 16X^2 + 25Y^2 - 160X - 200Y + 400 < 0

   Enter on the home screen
      FXY=16X^2+25Y^2-160X-200Y+400<0 [ENTER]

   Set the graph range to x: [-2,12], y: [-2,12] for a better view of
   this conic.

   Run the program
      IMPLGRAF [ENTER]

   A filled-in ellipse is then drawn in the first quadrant.

This program uses a brute force test of (nearly) each pixel on the
screen to determine if the pixel should be turn on.  The program
makes two passes over the screen filling in a quarter of the pixels
each time.  You get a good idea of how the function looks after the
first pass and may stop the program from filling in detail on the
second pass.