Re: [Rd] Fixing an only one coefficient in an ARIMA model

From: Prof Brian Ripley <>
Date: Thu, 30 Oct 2008 16:23:14 +0000 (GMT)

On Tue, 28 Oct 2008, Yohann MOREAU wrote:

> Good afternoon,
> I would like fitting an ARIMA model without the first coefficient.
> For example, I want to fit an AR(3) like this :
> y[t]=a[1]*y[t-1]+a[2]*y[t-2]+a[3]*y[t-3], where a[1]=0.
> How can I specify it in the function "arima", if it is possible ?

RTFM time:

    fixed: optional numeric vector of the same length as the total

           number of parameters.  If supplied, only 'NA' entries in
           'fixed' will be varied.  ' = TRUE' will be
           overridden (with a warning) if any AR parameters are fixed.
           It may be wise to set ' = FALSE' when fixing MA
           parameters, especially near non-invertibility.

> Thank you in advance.
> Yohann Moreau
> [[alternative HTML version deleted]]
> ______________________________________________
> mailing list

And this is a R-help question: please do study the posting guide.

Brian D. Ripley,        
Professor of Applied Statistics,
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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