"make.z" <-
  function(n=1,family="norm",mu=0,sigma=1) {
    m = 500
    res = c()
    if(family == "norm") {
      x = matrix(rnorm(n*m,mu,sigma),nrow=n)
    } else if(family== "exp") {
      if(mu == 0) mu = 1
      x = matrix(rexp(n*m,1/mu),nrow=n)
      sigma = 1/mu                      # for exp
    }
    res = apply(x,2,function(x) (mean(x)-mu)/(sigma/sqrt(n)))
    res
  }

"make.t" <-
  function(n=1,family="norm",mu=0,sigma=1) {
    m = 500
    res = c()
    if(family == "norm") {
      x = matrix(rnorm(n*m,mu,sigma),nrow=n)
    } else if(family== "exp") {
      if(mu == 0) mu = 1
      x = matrix(rexp(n*m,1/mu),nrow=n)
    }
    res = apply(x,2,function(x) (mean(x)-mu)/(sd(x)/sqrt(n)))
    res
  }