;;; Permute (shuffle): Return a random permutation of input vector. From Knuth
;;; "Algorithm P" (3rd ed, vol. 2, p. 145).
;;;   vec: vector to permute
;;; Note that rint will have to be replaced with a different RNG proc.
(define (permute vec)
  (do ((x (f64vector-quick-copy vec))
       (j (fx- (f64vector-length vec) 1) (fx- j 1)))
      ((= j 0) x)
    (f64vector-swap! x j (rint 0 j))))