R help - Jan 2011 - ARIMA simulation including a constant

Hi,

I have been looking at arima.sim to simulate the output from an ARMA model
fed with a normal and uncorrelated input series but I cannot find a way to
pass an intercept / constant into the model. In other words, the model input
in the function allows only for the AR and MA components but I need to pass
a constant.

Can anyone help?

Thanks

Paolo

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Sorry I am not really sure I have been taht clear.

I meant ARMA which is not bound to have zero mean. More precisely, suppose I
estimate y(t) = a + by(t-1)  + e(t) + ce(t-1) , i.e. and ARMA(1,1). My
question is how do I simulate values for yt given the values for a, b and c?
My problem with arima.sim is that I cannot find a way to pass the value for
the constant a.

Output from  R is:

Coefficient(s):
           Estimate  Std. Error  t value Pr(>|t|)
ar1         0.82978     0.01033   80.297  < 2e-16 ***
ma1         0.46347     0.01548   29.942  < 2e-16 ***
intercept  -0.02666     0.01012   -2.635  0.00841 **
---
Intercept is significant and I suppose it should be used if I want simulate
values from this ARMA(1,1)


Thanks and Apologies for not being clear

Paolo




On 3 January 2011 16:46, Prof Brian Ripley <ripley@stats.ox.ac.uk> wrote:
>  On Mon, 3 Jan 2011, Paolo Rossi wrote:
>
> Hi,
>>
>> I have been looking at arima.sim to simulate the output from an ARMA
model
>> fed with a normal and uncorrelated input series but I cannot find a way
to
>> pass an intercept / constant into the model. In other words, the model
>> input
>> in the function allows only for the AR and MA components but I need to
>> pass
>> a constant.
>>
>> Can anyone help?
>>
>
> Well, an ARIMA model by definition has zero mean (as the link on the help
> page for arima.sim to the exact definition tells you).  Perhaps you mean
> that (X-m) = Z follows an ARIMA model, in which case simulate Z and add m.
>  For a differenced ARIMA model it is not clear if you meant that you wanted
> an intercept for the original or differenced series: for the latter simply
> simulate the differenced series, add the intercept and use diffinv().
>
> Thanks
>>
>> Paolo
>>
>>        [[alternative HTML version deleted]]
>>
>
> Please do as we asked in the posting guide and not send HTML.
>
> --
> Brian D. Ripley,                  ripley@stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> 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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