R help - Oct 2011 - Undiff - order 7

Hello users.

I need a help again, please?

I runned my Arima model using difference order = 7
*
Y2=diff(Yst[,2],differences = 7)*
 Yfit=arima(Yst2,order=c(3,0,0),seasonal=list(order=c(0,0,0),period=7),include.mean=TRUE)

and forecast

Yfor=forecast.Arima(Yfit, h=31)

Now, I would like to compare the forecast with current values as:
seqplot.ts(current_st[,2],Yfor$mean,
colx="1",coly="red",ltyx=1,ltyy=2)

How the model will runned with a difference order = 7, this graph will not
be in the same scale.
I tryed to do:

prev <- cumsum(c(Yfor$mean))
prevst<-ts(prev, freq=365, start=c(2011,7))
seqplot.ts(Y1st[,2],prevst,
colx="1",coly="red",ltyx=1,ltyy=2)

But the graphic still strange. The forecast still bigger.
Somemeone could help me in this undiff in R, please?

Thanks
Flávio

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