Texas Instruments PLUS TI-89 - Manual (Page 165)

148 Chapter 9: Sequence Graphing
09SEQUEN.DOC TI-89/TI-92 Plus: Sequence Graphing (English) Susan Gullord Revised: 02/23/01 10:59 AM Printed: 02/23/01 2:14 PM Page 148 of 14
1. On the Y= Editor ( ¥ # ), define u1(n) = ë .8u1(n ì 1) + 3.6 . Set
initial value ui1 = ë 4 .
2. Set Axes = TIME .
3. On the Window Editor
( ¥ $ ), set the Window
variables.
nmin=1. xmin=0. ymin= ë 10.
nmax=25. xmax=25. ymax=10.
plotstrt=1. xscl=1. yscl=1.
plotstep=1.
4. Graph the sequence
( ¥ %).
By default, a sequence uses
the
Square display style.
5. On the Y= Editor, set Axes = WEB and Build Web = AUTO .
6. On the Window Editor, change
the Window variables.
nmin=1. xmin= ë 10. ymin= ë 10.
nmax=25. xmax=10. ymax=10.
plotStrt=1. xscl=1. yscl=1.
plotStep=1.
7. Regraph the sequence.
Web plots are always shown
as lines, regardless of the
selected display style.
8. Press …. As you press B, the trace cursor follows the web. The
screen displays the cursor coordinates nc , xc , and yc (where xc
and yc represent u(n ì 1) and u(n) , respectively).
As you trace to larger values of nc , you can see xc and yc approach
the convergence point.
1. On the Y= Editor ( ¥ # ), define u1(n) = 3.2u1(n м 1) м .8(u1(n ì 1)) 2 .
Set initial value ui1 = 4.45 .
2. Set Axes = TIME .
3. On the Window Editor
( ¥ $ ), set the
Window variables.
nmin=0. xmin=0. ymin= ë 75.
nmax=10. xmax=10. ymax=10.
plotStrt=1. xscl=1. yscl=1.
plotStep=1.
4. Graph the sequence
( ¥ % ).
Because the sequence
quickly diverges to large
negative values, only a few
points are plotted.
Example:
Convergence
Tip: During a trace, you can
move the cursor to a
specified n value by typing
the value and pressing
¸ .
Tip: When the nc value
changes, the cursor is on
the sequence. The next time
you press
B , nc stays the
same but the cursor is now
on the y=x reference line.
Example:
Divergence
u(n)
n
u(n)
y=x
u(n ì 1)
u(n)
n
y= ë .8x + 3.6