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This does an automatic fit of a multiplicative seasonal ARMA model to a series after the differencing operations have been determined. This follows the procedure described in Gomez and Maravall, "Automatic Modeling Methods for Univariate Series", in Peña, Tiao and Tsay, eds., "A Course in Time Series Analysis", New York: Wiley, 2001, and is very similar to the procedure used in X12-ARIMA.

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*
* @GMAutoFit(options)  series start end
* does an automatic fit of a multiplicative seasonal ARMA model to a series
* following the procedure described in Gomez and Maravall, Gomez and Maravall,
* "Automatic Modeling Methods for Univariate Series", in Peña, Tiao and Tsay,
* eds., "A Course in Time Series Analysis", New York: Wiley, 2001.
*
* Parameters:
*   series      Series to analyze
*   start end   Range to analyze [range of series]
*
* Options
*   DIFF=number of regular differencings[0]
*   SDIFFS=number of seasonal differencings[0]
*   CONST/[NOCONST]  Include constant in all models
*   REGULAR=maximum number of regular AR or MA parameters (each polynomial) [2]
*   SEASONAL=maximum number of seasonal AR or MA parameters (each polynomial) [1]
*   FULL/[NOFULL] FULL does an exhaustive search rather than the GM search
*   REPORT/[NOREPORT] shows a table with all the models examined
*
* Description:
*   @GMAUTOFIT searches for an approximate minimum BIC model with no more than
*   the
*
* Defines:
*   %%AUTOP,%%AUTOQ,%%AUTOPS,%%AUTOQS are the chosen number of regular AR,
*    regular MA,seasonal AR and seasonal MA lags
*
procedure GMAutoFit series  start end
type series    series
type integer   start end
*
option integer diffs    0
option integer sdiffs   0
option integer regular  2
option integer seasonal 1
option switch  const    0
option switch  report   0
option switch  full     0
*
local real      ic bestic
local integer   p q ps qs
local integer   blockrow
local integer   plower pupper qlower qupper
local report    gmreport
*
declare integer %%autop %%autoq %%autops %%autoqs
if report {
   report(use=gmreport,action=define)
   report(use=gmreport,atrow=1,atcol=1,span) "Search for Minimum BIC Model"
   report(use=gmreport,atrow=2,atcol=1,span) "Series "+%label(series)
   report(use=gmreport,atrow=3,atcol=1,span) "with "+diffs+" regular and "+sdiffs+" seasonal differences"
   report(use=gmreport,atrow=5,atcol=1,align=center) "AR" "MA" "AR(s)" "MA(s)" "LogL" "BIC"
}
*
* For the GM search, fix the regular ARMA model at (3,0) and do an exhaustive
* search over the seasonal parameters.
*
if full
   compute plower=0,pupper=regular,qlower=0,qupper=regular,blockrow=%reportrow+1
else
   compute plower=3,pupper=3,qlower=0,qupper=0
*
do p=plower,pupper
   do q=qlower,qupper
      do ps=0,seasonal
         do qs=0,seasonal
            boxjenk(ar=p,ma=q,sar=ps,sma=qs,$
               diffs=diffs,sdiffs=sdiffs,const=const,cvcrit=.001,noprint,maxl,method=bfgs) series start end
            compute ic=-2.0*%logl+%nreg*log(%nobs)
            if report ; report(use=gmreport,row=new,atcol=1) p q ps qs %logl ic
            if .not.%valid(bestic).or.ic<bestic
               compute %%autop=p,%%autoq=q,%%autops=ps,%%autoqs=qs,bestic=ic
         end do qs
      end do ps
   end do q
end do p
if full ; branch final
*
* Skip a line between blocks
*
if report ; report(use=gmreport,row=new)
*
* Fix the seasonal ARMA model at the optimal values from the previous step.
* Do an exhaustive search over the regular parameters
*
compute ps=%%autops,qs=%%autoqs
do p=0,regular
   do q=0,regular
      boxjenk(ar=p,ma=q,sar=ps,sma=qs,$
        diffs=diffs,sdiffs=sdiffs,const=const,cvcrit=.001,noprint,maxl,method=bfgs) series start end
      compute ic=-2.0*%logl+%nreg*log(%nobs)
      if report ; report(use=gmreport,row=new,atcol=1) p q ps qs %logl ic
      if p==0.and.q==0.or.ic<bestic
         compute %%autop=p,%%autoq=q,bestic=ic
   end do q
end do p
*
* Skip a line between blocks
*
if report ; report(use=gmreport,row=new)
*
* Fix the regular ARMA model at the optimal values from the previous step and
* search again over the seasonal parameters
*
compute blockrow=%reportrow+1
compute p=%%autop,q=%%autoq
do ps=0,seasonal
   do qs=0,seasonal
      boxjenk(ar=p,ma=q,sar=ps,sma=qs,$
        diffs=diffs,sdiffs=sdiffs,const=const,cvcrit=.001,noprint,maxl,method=bfgs) series start end
      compute ic=-2.0*%logl+%nreg*log(%nobs)
      if report ; report(use=gmreport,row=new,atcol=1) p q ps qs %logl ic
      if ps==0.and.qs==0.or.ic<bestic
         compute %%autops=ps,%%autoqs=qs,bestic=ic
   end do qs
end do ps
*
:final
if report {
   report(use=gmreport,action=format,atcol=1,tocol=4,width=6)
   report(use=gmreport,action=format,atcol=5,tocol=5,width=10)
   report(use=gmreport,action=format,atrow=blockrow,tag=minimum,special=onestar)
   report(use=gmreport,action=format,atcol=6,tocol=6,width=8,align=decimal)
   report(use=gmreport,action=show)
}
end