Texas Instruments TI-86 User Manual

Page 271

Chapter 19: Applications

259

19APPS.DOC TI-86, Chap 19, US English Bob Fedorisko Revised: 02/13/01 2:41 PM Printed: 02/13/01 3:05 PM Page 259 of 18

ᕥ Select

GRAPH

from the

GRAPH

menu to plot the graph of the

two populations over time.

ᕦ To see the direction field of the phase-plane solution, select

FORMT

from the

GRAPH

screen, and then set

DirFld

field

format.

ᕧ Select

INITC

from the

GRAPH

menu and delete the values for

[

and

[

ᕨ Select

GRAPH

from the

GRAPH

menu to display the direction

field of the phase-plane solution.

ᕩ To see a family of specific phase-plane solutions on top of the

direction field, select

INITC

from the

GRAPH

menu, and then

enter lists for

[

and

[

as shown.

[

1={2,6,7}

[

2={6,12,18}

µ Select

TRACE

from the

GRAPH

menu to display the graph with

the trace cursor.

¸ Press

to see how many foxes and how many rabbits are alive at

t=3

. (Round the values of

(foxes) and

(rabbits) to whole

numbers.) How many foxes and rabbits are alive at

t=6

? at

t=12

On what value of

and

do the phase-plane orbits seem to

converge? What is the significance of this value?