.. index::
   single: Lags
   single: Distributed Lags
   single: Almon lag
   single: G7 Command; sma
   single: Constraints

Distributed Lags
================

To easily estimate a polynomial distributed lag, in which the lag coefficients are constrained softly to lie along a certain degree of polynomial, use the *sma* command described here.

**sma <top> <first> <last> <order> [f]**
   The *sma* command imposes a series of constraints which "softly" require the regression coefficients between <first> and <last> to lie on a polynomial of degree order.  If the 'f' is present, the polynomial is "free" at the end; without the 'f', the polynomial will be assumed to be zero for the coefficient after <last>.

Examples::

   sma 100 a4 a9 3 f
   sma 100 a8 a16 1