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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(nN1) and Y represents u(n)). Press ~ repeatedly to draw the web
step by step, starting at
nMin. In Web format, the trace cursor follows this course.
1. It starts on the x-axis at the initial value u(nMin) (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 nMin, u(n) and u(nMin) 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=
L10
Ymax=10
Yscl=1
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