Texas Instruments TI-86 - Manual (Page 150)

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 20 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 20 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 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 ) à126
increases plotting time without increasing accuracy.
Stat plot and screen drawings
are not stored to fldPic.