lag a ts
ts=lagts(arg1[,arg2])
* arg1 = the order of differenciation (optional, set to 1 if not provided) or a ts
* arg2 (if arg1 was he order of differenciation) = a time series
* ts = the lagged time series
y=reshape(1:20,'1985m1') // create a ts y = lagts(x) // y is x lagged once. y = lagts(4,x) // y is x lagged four times y = lagts(-1,x) // y is x forwarded once