# EULER (Graphical Version) - TI 81

Introduction
This program plots an approximate solution for the differential equation  using Euler's method. These solutions can be superimposed on a slopefield by running the Slope Field program first. Previous graphs are not cleared for comparison purposes.

If you have not used one of the programs posted on this website before, you should read through the information in the Intro to Programming section first.

The Program
 :All-Off {All-Off is in Y-VARS under OFF} :Disp "INITIAL X" {Disp is in PRGM under I/O} :Input X {Input is in PRGM under I/O} :Disp "INITIAL Y" :Input Y :Disp "STEP SIZE" :Input H :Lbl 1 {Lbl is in PRGM under CTL} :0C {The 0 is a zero}{The arrow is STO } :Lbl 2 :X+HU :Y+Y1*HV {Y1 is in Y-VARS under FUNCTION} :Line(X,Y,U,V) {Line is in DRAW under Draw} :UX :VY :IS>(C,20) {IS> is in PRGM under CTL} :Goto 2 {Goto is in PRGM under CTL} :Pause {Pause is in PRGM under CTL} :Goto 1

Running the Program

You will need to enter a function  f(x,y) into Y1 before running the program. You should also adjust your WINDOW accordingly. The program will ask for an initial set of coordinates for X and Y. You will also need to provide a stepsize. This can be either positive or negative. The program will plot 20 steps and then pause. Hit ENTER to plot the next 20 steps, and so on.

To test the program try the following:
f(x,y)  =  x + y,
WINDOW: -4< x <4,  -4< y <4,
Initial X  =  0,  Initial Y  =  0,
Stepsize  =  0.05