LIST the program; you should now have:
10
CLS
20
N
;;
24
25
DIM
Y(24)
30
FOR
X
;;
1
TO
N
50
READ
Y(X)
60
SX
=
SX
+ X:XX =
XX
+
X*X
70
SY
=
SY
+
Y(X):XY
=
XY
+ X*Y(X)
80
NEXT
X
90
B = (N*XY - SX*SY) /
(N*XX
- SX*SX)
100
A = (SY - B*SX) / N
110
PRINT "FORECAST
FOR
PERIOD X
IS"
120
PRINT
Aj"
+
"j6j"
*
X"
200
DATA
1
60,
175,
1.40,
230
210
DATA
155,
215,
155,
225
220
DATA
215,
265, 220,
325
230
DATA
225,
270, 265,
290
240
DATA
275,
350,
255,
345
250
DATA
300,
330,
315,
380
Suppose the data in lines 200 through 250 represent quarterly sales figures for six
consecutive years. RUN the program to compute the trend line on the 24 quarters
of
data. You will not have to enter any data during execution, since the program reads
the data from the DATA satements.
If
you have entered the program changes and data
correctly, you will see the trend line equation:
FORECAST FOR PERIOD X IS
148.22463768116
+ 8.4086956521739 * X
Of
course, the time period assumed here is a quarter, so that the equation will predict
the sales for a specified quarter in the future. For example, to predict the first quarter
of
year seven (period 25), enter:
PRINT
148.225
+
8.4087
*
25
(The numbers are rounded
off
to three or four decimal places.) The result, 358.4425
which is displayed represents the trend line projection
of
sales to the next period in the
future.
A new type
of
variable, the
subscripted
variable,
has been introduced in this
experiment. While this experiment could have been performed without the use
of
a
subscripted variable, including it now will make the next experiment much easier.
The DIM Y(24) statement in line
25
defines the variable Y as a subscripted variable
having a maximum
of
24 storage locations allocated to it. These 24 storage locations
can be thought
of
as 24 separate variables:
YO),
Y(2), Y(3),
....
Y(24)
The number within the parentheses is called the SUbscript, and refers to the relative
position
of
the variable within the block
of
storage locations set aside by the
corresponding DIM (for
"DIMension")
statement. The block
of
storage locations is
called the Y
array.
Thus, the variable Y(X), used in lines
50
and 70, refers to
position X within the Y array.
93
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