[S] Recursive Occurrence; and sub-function

["José Ailton Alencar andrade" <andrade@inep.gov.br>]

Hello All,

     I have two question. Let the following program in S+ :

 gera.p
 function(w, lambda, theta, eta)
 {
  Pi <- function(f)
  {
   a^f/(gamma(f)^(M + N))
  }
  psi.r <- function(x)
  {
   (log(gamma(x + 1e-008)) - log(gamma(x)))/1e-008 - log(a)
  }
  a <- (lambda^(M + N) * prod(theta) * prod(eta))
  mu <- nlminb(start = 0.3, objective = psi.r, lo = 0, up =
 100)$parameters
  sig <- sqrt((2 * 1)/((N + M) * d1.psi(x = mu)))
  q <- function(t)
  {
   exp(-1/(2 * sig^2) * (t - mu)^2)
  }
  p <- rnorm(1, mu, sig)
  u <- runif(1, 0, 1)
  if(Pi(f = w) * q(t = p) > 0) {
   alpha <- min((Pi(f = p) * q(t = w))/(Pi(f = w) * q(t = p)), 1)
  }
  {
   alpha <- 1
  }
  novop <- ifelse(u <= alpha, p, w)
  novop

     Questions:

     1)when I run this program using the command:

 gera.p(w=0.4, lambda=30, theta=runif(30,0,1), eta=runif(52,0,1))

 So, the S+ put the following error message:
 Error in Pi(f = w): Recursive occurrence of default argument "a"
 Dumped

 But the object "a" is in first line of program. Why is it happening?

     2) In this same program, when I use a object "a" in sub-function
 psi.r, so it do not find "a", but clearly "a" was defined above!!!!


 THANKS

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