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.
pdl polynomial distributed lag specification.
sar seasonal autoregressive error specification.
sma seasonal moving average error specification.