Command Reference : Special Expression Reference
  
Special Expression Reference
The following reference is an alphabetical listing of special expressions that may be used in series assignment and generation, or as terms in estimation specifications.
Special Expression Summary
ar autoregressive error specification.
d fractional difference specification.
@expand automatic dummy variables.
ma moving average error specification.
na not available (missing value) code.
nrnd normal random number generation.
pdl polynomial distributed lag specification.
rnd uniform random number generation.
sar seasonal autoregressive error specification.
sma seasonal moving average error specification.
@wexpand automatic dummy variables from strings.