Texas Instruments TI-92 Owners Manual - Page 164

Using Web Plots, Valid Functions for Web Plots, When You Display the Graph Screen, Drawing the Web - 92 manual

Page 164 highlights

Using Web Plots A web plot graphs u(n) vs. u(nì 1), which lets you study the long-term behavior of a recursive sequence. The examples in this section also show how the initial value can affect a sequence's behavior. Valid Functions for Web Plots A sequence must meet the following criteria; otherwise, it will not be graphed properly on WEB axes. The sequence: ¦ Must be recursive with only one recursion level; u(nì 1) but not u(nì 2). ¦ Cannot reference n directly. ¦ Cannot reference any other defined sequence except itself. When You Display the Graph Screen After you select WEB axes and display the Graph screen, the TI-89 / TI-92 Plus: ¦ Draws a y=x reference line. ¦ Plots the selected sequence definitions as functions, with u(nì 1) as the independent variable. This effectively converts a recursive sequence into a nonrecursive form for graphing. For example, consider the sequence u1(n) = 5ìu1(nì1) and an initial value of ui1=1. The TI-89 / TI-92 Plus draws the y=x reference line and then plots y = 5ì x. Drawing the Web After the sequence is plotted, the web may be displayed manually or automatically, depending on how you set Build Web on the AXES dialog box. If Build Web = TRACE AUTO The web is: Not drawn until you press .... The web is then drawn step-by-step as you move the trace cursor (you must have an initial value before using Trace). Note: With WEB axes, you cannot trace along the sequence itself as you do in other graphing modes. Drawn automatically. You can then press ... to trace the web and display its coordinates. Note: The web starts at plotstrt. The value of n is incremented by 1 each time the web moves to the sequence (plotStep is ignored). The web: 1. Starts on the x axis at the initial value ui (when plotstrt = 1). 2. Moves vertically (either up or down) to the sequence. 3. Moves horizontally to the y=x reference line. 4. Repeats this vertical and horizontal movement until n=nmax. Chapter 9: Sequence Graphing 147

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Chapter 9: Sequence Graphing
147
A sequence must meet the following criteria; otherwise, it will not be
graphed properly on
WEB
axes. The sequence:
¦
Must be recursive with only one recursion level;
u(n
ì
1)
but not
u(n
ì
2)
.
¦
Cannot reference
n
directly.
¦
Cannot reference any other defined sequence except itself.
After you select
WEB
axes and display the Graph screen, the
TI
-
89 / TI
-
92 Plus:
¦
Draws a
y=x
reference line.
¦
Plots the selected sequence definitions as functions, with
u(n
ì
1)
as the independent variable. This effectively converts a recursive
sequence into a nonrecursive form for graphing.
For example, consider the sequence
u1(n) =
5
ì
u1(n
ì
1) and an
initial value of
ui1=1
. The
TI
-
89 / TI
-
92 Plus
draws the
y=x
reference
line and then plots
y =
5
ì
x
.
After the sequence is plotted, the web may be displayed manually or
automatically, depending on how you set
Build Web
on the
AXES
dialog box.
If Build Web =
The web is:
TRACE
Not drawn until you press
. The web is then
drawn step-by-step as you move the trace cursor
(you must have an initial value before using
Trace
).
Note:
With
WEB
axes, you cannot trace along the
sequence itself as you do in other graphing modes.
AUTO
Drawn automatically. You can then press
to
trace the web and display its coordinates.
The web:
1.
Starts on the x axis at the initial value
ui
(when
plotstrt = 1
).
2.
Moves vertically (either up or down) to the sequence.
3.
Moves horizontally to the
y=x
reference line.
4.
Repeats this vertical and horizontal movement until
n
=
nmax
.
Using Web Plots
A web plot graphs u(n) vs. u(n
ì
1), which lets you study the
long-term behavior of a recursive sequence. The examples in
this section also show how the initial value can affect a
sequence’s behavior.
Valid Functions for
Web Plots
When You Display
the Graph Screen
Drawing the Web
Note:
The web starts at
plotstrt. The value of n is
incremented by 1 each time
the web moves to the
sequence (plotStep is
ignored).