sicp习题试解 (2.37)

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;

; Structure and Interpretation of Computer Programs

; (trial answer to excercises)

;

; 计算机程序的构造和解释(习题试解)

;

; created: code17 08/19/05

; modified:

; (保持内容完整不变前提下，可以任意转载)

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;; SICP No.2.37

(define (matrix-*-vector m v)

(map (lambda (x) (dot-product x v)) m))

(define (transpose mat)

(accumulate-n cons () mat))

(define (matrix-*-matrix m n)

(let ((cols (transpose n)))

(map (lambda (x) (matrix-*-vector cols x)) m)))

;; Test-it:

;; Welcome to MzScheme version 209, Copyright (c) 2004 PLT Scheme, Inc.

;; > (define m (list (list 1 2 3 4) (list 4 5 6 6) (list 6 7 8 9)))

;; > (define v (list 4 3 2 1))

;; > (matrix-*-vector m v)

;; (20 49 70)

;; > > (transpose m)

;; ((1 4 6) (2 5 7) (3 6 8) (4 6 9))

;; > (matrix-*-matrix m (transpose m))

;; ((30 56 80) (56 113 161) (80 161 230))