# Writing a function n R [closed]

Hello, How Can i write this function in R? and any simulation codes about SETAR model including codes, links, books or any guide, would be appreciated.? Thanks in advance

Please expect this to be removed from CrossValidated soon and moved to stackoverflow or something like this, as your question is mostly about programming.

If you can't write this function, I wonder, what you will do with it. However, this should be your function in R:

X_t <- function(X_tminus1, lambda_tminus1){
if(X_tminus1 <= 4)
lambda <- .9+.2*X_tminus1 + .4*lambda_tminus1
else
lambda <- 2.2 + .3*X_tminus1 + .5*lambda_tminus1
return(list(lambda = lambda, X_t = rpois(1, lambda)))
}


I guess, you likely want to produce time series with this. This is an example that should work (no guarantee, though. Please test before usage):

X_t <- function(X_tminus1, lambda_tminus1){
if(X_tminus1<=4)
lambda <- .9+.2*X_tminus1 + .4*lambda_tminus1
else
lambda = 2.2 + .3*X_tminus1 + .5*lambda_tminus1
return(list(lambda=lambda, X_t=rpois(1, lambda)))
}

create_n_values <- function(X, lambda, n){
xs <- numeric(n)
for(i in 1:n){
X_t_val <- X_t(X, lambda)
X <- X_t_val[[1]]
lambda <- X_t_val[[2]]
xs[i] <- X
}
return(xs)
}

#example create 25 values wit X_tminus1=1 and lambda_tminus1=1:
create_n_values(X=1, lambda=1, n=25)