#' Generate multivariate seasonal component
#'
#' generates a component that is seasonally (12) difference stationary
#'
#' @param n length of series
#' @param Phi seasonal autoregressive parameter
#' @param Sig covariance martrix white noise component
#' @param burn burn in (defaults to 1000)
#' @param seasonl.period periodicity of component (defaults to 12)
#'
#' @return Ndim x n matrix of observations
#' @export
#'
gen_seasComp = function(n, Phi, Sig, burn=10^3, seasonal.period=12){
N = n+burn
Ndim = dim(Sig)[1]
if(Ndim==1 || is.null(Ndim)){ # handle univariate case first
w = rnorm(n = N, mean = 0, sd = sqrt(Sig))
s = rep(NA, N) # storage
s[1:seasonal.period] = w[1:seasonal.period] # initial values
for(i in (seasonal.period+1):N){
new.s = -1*sum(s[(i-seasonal.period+1):(i-1)]) + w[i]
s[i] = new.s
}
return(s[(burn+1):N])
} # end of univariate if() statement
w = mvtnorm::rmvnorm(n = N, mean = rep(0,Ndim), sigma = Sig)
s = matrix(NA, N, Ndim) # storage
s[1:seasonal.period, ] = w[1:seasonal.period, ] # initial values
for(i in (seasonal.period+1):N){
new.s = -1*colSums(s[(i-seasonal.period+1):(i-1), ]) + w[i,]
s[i, ] = t(new.s)
}
return(s[(burn+1):N, ])
}
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