*
* Example NONLIN.DAT from pp 211-212
*
open data nonlin.dat
data(format=free,org=columns) 1 31 time actual logactual
*
graph(footer="Figure 6-2 Slight nonlinear trend")
# actual
*
* You can get the second difference directly with the DIFFERENCE instruction with
* the option DIFFS=2.
*
diff actual / act1d
diff(diffs=2) actual / act2d
*
stats act2d
set fit2d * 32 = 2*actual{1}-actual{2}+%mean
set err2d = actual-fit2d
*
print(picture="*.##") / actual act1d act2d fit2d err2d
*
* Analysis of the log series.
*
diff logactual / log1d
stats log1d
*
* Compute the fitted value in log form, then take the exp of it to get back to
* levels.
*
set fitlog * 32 = exp(logactual{1}+%mean)
set errlog = actual-fitlog
*
print(picture="*.##") / logactual log1d fitlog errlog