Program:	DIFFEQ
Author:	Dave Gaebler
February 17, 1999

Variables used:A,B,C,D,E,F,G,H,N,X,Y,,Str1,n,u(n)
This program approximates solutions to the differential equation dy/dx=f(x,y).  You enter 
dy/dx, x1, and y1.  Then you can do two things: (1) Graph the approximation.  The graph is a
bunch of points which will be erased if you change the window.  This option uses the Runge-
Kutta method.  (2) Find the approximate y-value at a given x-value.  This is done with the
Euler method.  When you enter dy/dx, you must use certain expressions instead of x and y. 
Sorry, it's the only way I could get it to work.  For example, if dy/dx=x/y, enter 
dy/dx=(H(n-1)+A)/u(n-1).  Be sure not to use quotes, as dy/dx is stored in a string.  Also,
if you want to find the y-value at x=c, make sure c-x1 is an integer multiple of h.  I know,
it's quite limited, but it's the best I could do.  
Oh yeah, there is an endless loop asking you to input the x-value.  Don't panic; you can
escape by pressing ON.