The User Defined model
When you set the model to user defined it means that you are expected to supply the complete equation,
including the values of any coefficients. The calculator will not calculate the values of any variables you
include. For example, if you were to supply an equation of
A/(X–B)
as your model then the calculator would
use the values of
A
and
B
currently in memory. By repeatedly adjusting the values of
A
and
B
in
HOME
you
could find the best version of the curve for the data.
This may seem to be a useless model but it can be quite useful if you want to experiment with a model that is
not one of those supplied with the calculator.
Connected data
One of the settings on the second page of the
PLOT SETUP
screen can
be useful for some types of data. For example, one of the common tasks
in many mathematical courses is the analysis of time series data.
Unlike most bivariate data, time series values are usually plotted as a
line graph - i.e. as connected points. This facilitated by
Connect
.
For example:
The sales of an ice-cream shop are shown as quarterly sales figures for the
years 1992 to 1993. Display this data on a line graph.
Yr
1992
1993
Qtr
1 2 3 4 1 2 3 4
Sales 12 18 20 15 13 20 23 16
($1000)
The result (with
Connect
checked) is shown right. Notice that although
the
X
values in the table were 1, 2, 3, 4, 1, 2, 3, 4 we can’t use them
that way because it would result in 1992 Qtr 1 being graphed on top of
1993 Qtr 1. The graph on the right was produced by entering values of
1992, 1992.25, 1992.5, 1992.75 etc.
This is not the end of the story though. When you activate
Connect
the calculator will always sort the points
into ascending order based on their x values before graphing. Thus (1,3) (5,4) (2,7) would be graphed as
(1,3) (2,7) (5,4). Not doing this would result in a graph that doubled back on itself and looked like a
scribble instead of a line graph.
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