Calculator User Manual

138
Chapter 10: Differential Equation Graphing
10DIFFEQ.DOC TI-86, Chap 10, US English Bob Fedorisko Revised: 02/13/01 2:28 PM Printed: 02/13/01 3:02 PM Page 138 of 2010DIFFEQ.DOC TI-86, Chap 10, US English Bob Fedorisko Revised: 02/13/01 2:28 PM Printed: 02/13/01 3:02 PM Page 138 of 2010DIFFEQ.DOC TI-86, Chap 10, US English Bob Fedorisko Revised: 02/13/01 2:28 PM Printed: 02/13/01 3:02 PM Page 138 of 20
The Built-In Variable fldPic
As the TI
-
86 plots a field, it stores the field and any displayed label, axes, or cursor
coordinate information to the built-in variable
fldPic
.
These actions do not update
fldPic
.
♦
Switching the solving method format from
RK
to
Euler
or from
Euler
to
RK
♦
Entering or editing any initial condition variable value (
Q
[
1
through
Q
[
9
)
♦
Editing a value for
difTol
,
EStep
,
tMin
,
tMax
,
tStep
, or
tPlot
♦
Changing a graph style
These actions update
fldPic
.
♦
Editing an equation in the equation editor
♦
Re-assigning an axis, editing a
dTime
value, or editing a
fldRes
value
♦
Using a
GRAPH ZOOM
menu item
♦
Changing a format setting other than solving method format
♦
Editing a value for
xMin
,
xMax
,
xScl
,
yMin
,
yMax
, or
yScl
Displaying the Graph
To plot the differential equations, you can select
GRAPH
,
TRACE
,
EVAL
, or
STGDB
, or a
DRAW
,
ZOOM
, or
STPIC
operation, from the
GRAPH
menu. The TI
-
86 solves each equation
from
tMin
to
tMax
. If
t
is not an axis, it plots each point beginning at
tPlot
; otherwise, it
begins at
tMin
. As a graph is plotted, the variables
x
,
y
,
t
, and
Q
n
are updated.
tStep
affects trace resolution and graph appearance, but not the accuracy of the trace
values.
tStep
does not determine the step size for solving; using the
RK
algorithm (Runge-
Kutta 2-3) determines the step size. If the x-axis is
t
, setting
tStep
<(
tMax
N
tMin
)
à
126
increases plotting time without increasing accuracy.
Stat plot and screen drawing
s
are not stored to
fldPic
.