Chapter 6: Sequence Graphing
110
Note:
A potential convergence point occurs whenever a sequence intersects the
y=x
reference
line. However, the sequence may or may not actually converge at that point, depending on the
sequence’s initial value.
Drawing the Web
To activate the trace cursor, press
r
. The screen displays the sequence and the current
n
, X,
and Y values (X represents
u(
n
N
1)
and Y represents
u(
n
)
). Press
~
repeatedly to draw the web
step by step, starting at
n
Min
. In Web format, the trace cursor follows this course.
1. It starts on the x-axis at the initial value
u(
n
Min)
(when
PlotStart=1
).
2. It moves vertically (up or down) to the sequence.
3. It moves horizontally to the
y=x
reference line.
4. It repeats this vertical and horizontal movement as you continue to press
~
.
Using Web Plots to Illustrate Convergence
Example: Convergence
1. Press
o
in
Seq
mode to display the sequence Y= editor. Make sure the graph style is set to
í
(dot), and then define
n
Min
,
u(
n
)
and
u(
n
Min)
as u(n) = -.8u(n-1) + 3.6.
2. Press
y
.
Í
to set
Time
axes format.
3. Press
p
and set the variables as shown below.
4. Press
s
to graph the sequence.
5. Press
y .
and select the
Web
axes setting.
nMin=1
nMax=25
PlotStart=1
PlotStep=1
Xmin=0
Xmax=25
Xscl=1
Ymin=
L
10
Ymax=10
Yscl=1
