*
* Example DUMMY5.DAT from page 437
*
open data dummy5.dat
data(format=free,org=columns) 1 20 time demand improve time timeximp
*
* You can create the variables used (other than demand) with
* set improve = t>=11
* set time    = t
* set timeximp = t*improve
*
linreg demand
# constant improve time timeximp