blob: e28e91b01b18ddd4c3155403bfba67793329e628 (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
|
;;;; Under Creative Commons Attribution-ShareAlike 4.0
;;;; International. See
;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
(define-module (net ricketyspace sicp two eleven)
#:use-module (net ricketyspace sicp two seven)
#:export (mul-interval-alt))
(define (mul-interval-alt x y)
(define lbx (lower-bound x))
(define ubx (upper-bound x))
(define lby (lower-bound y))
(define uby (upper-bound y))
(define (n a) (< a 0)) ; is negative
(define (p a) (>= a 0)) ; is positive
(define (signs slbx subx slby suby)
(and (slbx lbx)
(subx ubx)
(slby lby)
(suby uby)))
(cond ((signs n p p p) (make-interval (* lbx uby) (* ubx uby)))
((signs p p n p) (make-interval (* ubx lby) (* ubx uby)))
((signs p p p p) (make-interval (* lbx lby) (* ubx uby)))
((signs n n n n) (make-interval (* lbx lby) (* ubx uby)))
((signs n n p p) (make-interval (* ubx uby) (* lbx lby)))
((signs p p n n) (make-interval (* ubx uby) (* lbx lby)))
((signs n n n p) (make-interval (* ubx uby) (* ubx lby)))
((signs n p n n) (make-interval (* ubx uby) (* lbx uby)))
((signs n p n p) (make-interval (min (* lbx uby) (* ubx lby))
(* ubx uby)))
(else (error "Intervals not supported"))))
;;; Guile REPL
;;;
;;; scheme@(guile-user)> ,use (net ricketyspace sicp two eleven)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval -2 -3) (make-interval 5 7))
;;; $8 = (-21 . -10)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval 2 3) (make-interval -5 -7))
;;; $9 = (-21 . -10)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval -2 3) (make-interval -5 7))
;;; $10 = (-15 . 21)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval -2 -3) (make-interval -5 7))
;;; $11 = (-21 . 15)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval -2 3) (make-interval -5 -7))
;;; $12 = (-21 . 14)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval -2 3) (make-interval 5 7))
;;; $13 = (-14 . 21)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval 2 3) (make-interval -5 7))
;;; $14 = (-15 . 21)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval 2 3) (make-interval 5 7))
;;; $15 = (10 . 21)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval -2 -3) (make-interval -5 -7))
;;; $16 = (10 . 21)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval -2 -3) (make-interval 5 7))
;;; $17 = (-21 . -10)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval 2 3) (make-interval -5 -7))
;;; $18 = (-21 . -10)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval -2 -3) (make-interval -5 7))
;;; $19 = (-21 . 15)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval -2 3) (make-interval -5 -7))
;;; $20 = (-21 . 14)
;;; scheme@(guile-user)> (mul-interval-alt (make-interval -2 3) (make-interval -5 7))
;;; $21 = (-15 . 21)
|