Texas Instruments TI-89 Titanium User Manual page 425

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
.
EQUATIONS
2. In the Y= Editor (8 #), define the
differential equations and enter the
initial conditions.
To speed up graphing times, clear
Note:
any other equations in the Y= Editor. With
, all equations are evaluated even
FLDOFF
if they are not selected.
3. Press:
,
9
— or —
@ 8 Í Set
Solution Method = RK
Fields = FLDOFF
Differential Equation Graphing
Graph = DIFF
,
Axes = ON Labels = ON
, and
.
,
422