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ex2.37.scm
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ex2.37.scm
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(define (accumulate op initial sequence)
(if (null? sequence)
initial
(op (car sequence)
(accumulate op initial (cdr sequence)))))
(define (accumulate-n op init seqs)
(if (null? (car seqs))
nil
(cons (accumulate op init (map car seqs))
(accumulate-n op init (map cdr seqs)))))
(define (dot-product v w)
(accumulate + 0 (map * v w)))
(dot-product (list 1 2 3) (list 4 5 6))
(define matrix (list (list 1 2 3 4) (list 4 5 6 6) (list 6 7 8 9)))
(define (matrix-*-vector m v)
(map (lambda (x) (dot-product x v)) m))
(matrix-*-vector matrix (list 1 1 1 1))
(define (transpose mat)
(accumulate-n cons nil mat))
(define nil '())
(transpose matrix)
(define (matrix-*-matrix m n)
(let ((cols (transpose n)))
(map (lambda (x) (matrix-*-vector cols x)) m)))
(define matrix1 (list (list 1 4 6) (list 2 5 7) (list 3 6 8) (list 4 6 9)))
(matrix-*-matrix matrix matrix1)
(matrix-*-matrix matrix1 matrix)