[R] Specifying Transfer Function in Time series Intervention model

[Subhadip Nath]

Hi Team, 

I am running ARIMAX with TSA package.  my code is
fit2 <- arimax(yseries, order = c(1,0,1),xtransf =
data.frame(X1var),transfer=list(c(1,0)))
my question is
1st Q.--> If I need to take difference of X1var then what should i do?. What
i am doing like submitting R code as 
X1vard <- diff(X1var)
and then i am including in the xtransf.  Same time if  i need to take
difference of yseries 
yseriesd<-diff(yseries)
here ARIMAX order = c(1,0,1) i have to keep. ARIMAX order = c(1,1,1) is
giving error. Hope this is correct procedure.

2nd Q -->>In the transfer = list(c(1,0), 1 is Autoregressive operator
function and 0 is Moving average operator. I am not able to change the value
of MA operator. I am receiving an error message 
"Error in optim(init[mask], armaCSS, method = "BFGS", hessian = FALSE,  : 
  initial value in 'vmmin' is not finite"
I am using R 2.15.1 version.

3rd Q --> If i need to take Lag values of X1var. how to incorporate in the
model.

Warm regards,
Subhadip


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