z.test <- function(x, alternative="two.sided", mu, popu.var) {
n <- length(x)
xmean <- mean(x)
eta <- abs(xmean - mu)
return(1 - pnorm(eta, mean=0, sd=sqrt(popu.var/n)) + pnorm(-eta, mean=0, sd=sqrt(popu.var/n) ))
}