Texas Instruments TI-89 Manual Book page 202

Selecting an Initial
Condition
Interactively from
the Graph Screen
Note: With or
SLPFLD
, you can select
DIRFLD
initial conditions interactively
regardless of whether you
enter initial conditions in the
Y= Editor.
Note: With , you
FLDOFF
can select initial conditions
interactively. However, if
three or more equations are
entered, you must enter a
single value (not a list) as
the initial condition for each
equation in the Y= Editor.
Otherwise, a Dimension
error occurs when graphing.
Note about Tracing
a Solution Curve
When a differential equation is graphed (regardless of whether a
solution curve is displayed), you can select a point on the Graph
screen and use it as an initial condition.
If Fields = Do this:
1. Press:
SLPFLD
– or – TI-89
DIRFLD TI-92 Plus:
2. Specify an initial condition. Either:
¦
Move the cursor to the applicable point and
press ¸.
– or –
¦
For each of the two coordinates, type a value
and press ¸.
A circle marks the initial condition and the solution
curve is drawn.
1. Press:
FLDOFF
TI-89
TI-92 Plus:
You are prompted to select the axes for which you
want to enter initial conditions.
Your selections will be used as the axes for the
graph.
2. You can accept the defaults or change them. Then
press ¸.
3. Specify an initial condition as described for
SLPFLD
When you enter initial conditions in the Y= Editor or let
graph solution curves automatically, you can use ... to trace the
curves.
However, you cannot trace a curve drawn by selecting an initial
condition interactively. These curves are drawn, not plotted.
Chapter 11: Differential Equation Graphing
: 2 Š
Š
For (1st-order only), enter values
SLPFLD
for t0 and y(t0) .
For (2nd-order or system of two 1st-
DIRFLD
order equations only), enter values for both
initial conditions, where
y(t0)
set in the Y= Editor or Window Editor.
: 2 Š
Š
or .
DIRFLD
is the value
t0
t is a valid selection.
It will let you specify
a value for t0.
ncurves
185