numbers.lisp/lerp: The correct version is numerically stable,

(defun lerp (v a b)

  "Returns the result of linear interpolation between A and B, using the

interpolation coefficient V."

   (+ a (* v (- b a))))

  ;; The correct version is numerically stable, at the expense of an

  ;; extra multiply. See (lerp 0.1 4 25) with (+ a (* v (- b a))). The

  ;; unstable version can often be converted to a fast instruction on

  ;; a lot of machines, though this is machine/implementation

  ;; specific. As alexandria is more about correct code, than

  ;; efficiency, and we're only talking about a single extra multiply,

  ;; many would prefer the stable version

  (+ (* (- 1.0 v) a) (* v b)))

(declaim (inline mean))

(defun mean (sample)

    (lerp 0.1 1 2)

  1.1)

(deftest lerp.3

    (lerp 0.1 4 25)

  6.1)

(deftest mean.1

    (mean '(1 2 3))

  2)