From Newsgroup: comp.lang.lisp

andrew.baine wrote:

I'm looping over two variables to maximize a function, returning x and
y that maximize f. Any way to do it without the setf in the body?

; Here's a function you can paste to the REPL.

(defun f (x y)
(- (+ (* 9 x) (* 4 y))
(* x x)
(* y y))

A parenthesis is missing.

; And here's what I'm trying to do:

(let ((best-x -1)
(best-y -1)
(max nil))
(loop :for x :below 10 :do
(loop :for y :below 10 :do
(let ((n (f x
y)))
(if (or (null max) (> n
max))
(setf best-x
x
best-y
y
max n)))))
(values best-x best-y))

Gauche Scheme

(use util.combinations) ;; cartesian-product
(use gauche.collection) ;; find-max

(define (f x y)
(- (+ (* 9 x) (* 4 y))
(* x x)
(* y y)))

(find-max
(cartesian-product (list (iota 10) (iota 10)))
:key (cut apply f <>))

===>
(5 2)

Another solution: (4 2)


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