Texas Instruments TI-84 Plus Manual page 32

TI-84 Plus.) As you did when finding an exponential equation for data, large input values must
be aligned or an error or possibly an incorrect answer could be the result.
Note that the calculator finds a "best-fit" logistic function rather than a logistic function
with a limiting value L such that no data value is ever greater than L. We illustrate finding a
logistic function using the data in Table 1.2.1 of Section 1.4 in Calculus Concepts.
Time (in hours)
Total number of infected
computers(in thousands)
Clear any old data. Delete any functions in the
above table with the hours after 8
Construct a scatter plot of the data. An inflection point is
indicated, and the data appear to approach limiting values on
the left and on the right. A logistic model seems appropriate.
To find the logistic function and paste the equation into the
location of the
Y1
[Logistic] VARS
Note: Calculator menu items can be chosen by using
and pressing
ENTER .
indicated in the instruction above, you can scroll down the list of functions until
highlighted and press
Press
ENTER .
the other equations.
Note that the calculator uses the variable c for the value that the
text calls L.
Press
GRAPH
function drawn on the scatter plot.
The limiting value, in this context, is about 10 computers. The
two horizontal asymptotes are y = 0 (the line lying along the x-
axis) and the line y ≈ 10. To see the upper asymptote drawn on
a graph of the data, enter 10 in
•
Provided the input values are evenly spaced, program
trying to determine if a logistic model is appropriate for certain data. If the first
differences (in list
end small, this is an indication that a logistic model may provide a good fit to the data.
32
0.1
. . in list
A M
list, press
Y= STAT ► [CALC] ALPHA B
► [Y−VARS] 1 [Function] 1 [Y1].
For instance, instead of choosing
ENTER .
This equation may take longer to generate than
(or
ZOOM 9 [ZoomStat])
and press
Y2
after running program
L3
0 0.5 1 1.5
0.597 2.851 7.148
list and turn on
Y=
and the number of computers in list
L1
to scroll to the location of the item
▼
Logistic
to see the graph of the
.
GRAPH
might be helpful when you are
DIFF
) begin small, peak in the middle, and
DIFF
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Chapter 1
2 2.5
9.403 9.900
. Enter the data in the
Plot 1
:
L2
by pressing
ALPHA B
is
B
as