(defun poisson(lamb)
  ;Generates a poisson distibuted ranom number with intensity lambda
  (let 
      ((x  (randexp 1))
      (rand  0))
    (while (< x lamb)
       (setf x (+ x (randexp 1)))
       (setf rand (+ rand 1))
       )
    rand))


(defun randexp(m)
  ;Generates a random number from a exponential distribution
  ;with expeced value m,
  (- (* m (log (my-random 1.)))))