Texas Instruments PLUS TI-89 - Manual (Page 193)

176 Chapter 11: Differential Equation Graphing
11DIFFEQ.DOC TI-89/TI-92 Plus: Differential Equation (English) Susan Gullord Revised: 02/23/01 11:04 AM Printed: 02/23/01 2:15 PM Page 176 of 26
Steps
³
TI-89
Keystrokes
›
TI-92 Plus
Keystrokes Display
1. Display the MODE dialog box.
For Graph mode, select
DIFF EQUATIONS .
3
B 6
¸ 3
B 6
¸
2. Display and clear the Y= Editor.
Then define the 1st-order
differential equation:
y1'(t)=.001y1 щ (100 м y1)
Press p to enter the ù shown above.
Do not use implied multiplication
between the variable and
parentheses. If you do, it is treated as
a function call.
Leave the initial condition yi1 blank.
¥ #
ƒ 8 ¸
¸.0 0 1
Y 1 p c 1 0 0
| Y 1 d ¸ ¥ #
ƒ 8 ¸
¸ . 0 0 1
Y 1 p c 1 0 0
| Y 1 d ¸
3. Display the GRAPH FORMATS
dialog box. Then set Axes = ON ,
Labels = ON , Solution Method =
RK , and Fields = SLPFLD .
Important: To graph one differential
equation, Fields must be set to
SLPFLD or FLDOFF . If Fields= DIRFLD ,
an error occurs when you graph.
¥ Í
D D B 2
D D B 2
D B 1
D B 1 ¸ ¥ F
D D B 2
D D B 2
D B 1
D B 1 ¸
4. Display the Window Editor, and
set the Window variables as
shown to the right.
¥ $
0 D 1 0 D
. 1 D 0 D
· 1 0 D 1 1 0
D 1 0 D · 1 0
D 1 2 0 D
1 0 D 0 D.0 0 1
D 2 0 ¥ $
0 D 1 0 D
. 1 D 0 D
· 1 0 D 1 1 0
D 1 0 D · 1 0
D 1 2 0 D
1 0 D 0 D . 0 0
1 D 2 0
5. Display the Graph screen.
Because you did not specify an initial
condition, only the slope field is
drawn (as specified by
Fields=
SLPFLD in the GRAPH
FORMATS dialog box).
¥ % ¥ %
Preview of Differential Equation Graphing
Graph the solution to the logistic 1st-order differential equation y' = .001y щ (100 м y). Start
by drawing only the slope field. Then enter initial conditions in the Y= Editor and
interactively from the Graph screen.
Important: With y1'
selected, the
TI
- 89 / TI - 92 Plus will graph
the y1 solution curve, not
the derivative y1'.