# [R] how to check convergence of arima model

Wed Jul 4 11:38:26 CEST 2012

```Hello,

Put the fitted models in a list and then use lapply with AIC(). Like this

set.seed(1)
x <- 1:100 + sqrt(1:100 + runif(100)) + rnorm(100)
models <- list()
models[[1]] <- arima(diff(x), order = c(1, 0, 0))  # Just to show
models[[2]] <- arima(diff(x), order = c(1, 0, 1))  # several
models[[3]] <- arima(diff(x), order = c(2, 0, 2))  # models
models[[4]] <- arima(diff(x), order = c(2, 0, 3))
lapply(models, AIC)

Or run each model at a time through AIC(), whichever suits better.

Hope this helps

Em 04-07-2012 10:22, Sajeeka Nanayakkara escreveu:
> Hi,
>
> I need to predict exchange rates using time series. So according to ACF
> and PACF knowledge, mixed model (ARIMA) be the appropriate and now, I
> need to find order of the model (p,d,q). So, several models were fitted
> to select the suitable model using arima().
>
> Could you please tell me the procedure of selecting the correct order as
> I don't have enough time to search?
>
> Thank you.
>
> Sajeeka Nanayakkara
>
>
>
>
>
> ------------------------------------------------------------------------
> *To:* Sajeeka Nanayakkara <nsajeeka at yahoo.com>
> *Cc:* r-help at r-project.org
> *Sent:* Wednesday, July 4, 2012 2:58 PM
> *Subject:* Re: [R] how to check convergence of arima model
>
> Hello,
>
> Inline.
>
> Em 04-07-2012 09:35, Sajeeka Nanayakkara escreveu:
>  > Hi,
>  >
>  > Sorry, since I didn't see the earlier message I resend it.
>  >
>  > I read the help page that you mentioned. But the problem is for all
>  > models, code is zero. According to that, all models were converged.
>  > Considering AIC value the best model is selected.
>
> No, arima() does not select models by AIC. That is the default behavior
> of ar(); arima() does NOT select models, it selects, using optim, values
> for the parameters of a specified model. You must choose the orders
> yourself.
>
> Hope this helps,
>
>
>  >
>  > Is that correct procedure?
>  >
>  > The R code which was used is;
>  > model1<-arima(rates,c(1,1,1))
>  > model1
>  > model1\$code
>  > [1] 0
>  >
>  > Sajeeka Nanayakkara
>  >
>  >
>  >
>  > ------------------------------------------------------------------------
>  > *To:* Sajeeka Nanayakkara <nsajeeka at yahoo.com
> <mailto:nsajeeka at yahoo.com>>
>  > *Cc:* r-help at r-project.org <mailto:r-help at r-project.org>
>  > *Sent:* Wednesday, July 4, 2012 2:01 PM
>  > *Subject:* Re: [R] how to check convergence of arima model
>  >
>  > Hello,
>  >
>  > Inline.
>  >
>  > Em 04-07-2012 08:02, Sajeeka Nanayakkara escreveu:
>  >  > I have already fitted several models
>  >  > using R code; arima(rates,c(p,d,q))
>  >  >
>  >
>  > And I have already answered to a question starting like this yesterday.
>  > In the mean time, the subject line changed.
>  >
>  >  >
>  >  > As I heard, best model produce the
>  >  > smallest AIC value, but maximum likelihood estimation procedure
> optimizer
>  >  > should converge.
>  >  >
>  >  >
>  >  > How to check whether maximum likelihood estimation procedure
>  > optimizer has converged or not?
>  >
>  > Yes, it was this question, the subject line was 'question'...
>  >
>  > ... And the answer was: read the manual, that I quoted, by the way.
>  >
>  > It now changed to: read the manual, period.
>  >
>  >
>  >  >    [[alternative HTML version deleted]]
>  >  >
>  >  > ______________________________________________
>  >  > R-help at r-project.org <mailto:R-help at r-project.org>
> <mailto:R-help at r-project.org <mailto:R-help at r-project.org>> mailing list
>  >  > https://stat.ethz.ch/mailman/listinfo/r-help
>  > http://www.R-project.org/posting-guide.html
>  >  > and provide commented, minimal, self-contained, reproducible code.
>  >  >
>  >
>  >
>  >
>
>
>

```