Texas Instruments TITANIUM TI-89 User Manual

Page 436

Differential Equation Graphing

436

Predator-Prey Model

Use the two coupled 1st-order differential equations:

y1' = Ly1 + 0.1y1 ùy2 and y2' = 3y2 Ny1 ùy2

where:

y1 = Population of foxes

yi1 = Initial population of foxes (2)

y2 = Population of rabbits

yi2 = Initial population of rabbits (5)

1. Use

3 to set

Graph = DIFF

EQUATIONS

2. In the Y= Editor (

8 #), define the

differential equations and enter the
initial conditions.

Note:

To speed up graphing times, clear

any other equations in the Y= Editor. With

FLDOFF

, all equations are evaluated even

if they are not selected.

3. Press:

— or —

8 Í Set

Axes = ON

Labels = ON

Solution Method = RK

, and

Fields = FLDOFF