sigmoid <- function(z){
 
  #   Compute sigmoid function
  #
  #   g <- sigmoid(z) computes the sigmoid of z.
  
  # ====================== YOUR CODE HERE ======================
  # Instructions: Compute the sigmoid of each value of z 
  #               (z can be a matrix, vector or scalar).
  
  
  
  # ============================================================
  return(g)
}