(define (dot-product v w)
(accumulate + 0 (map * v w)))
(define (matrix-*-vector m v)
(map (lambda (x) (dot-product x v)) m))
(define (transpose mat)
(accumulate-n cons nil mat))
(define (matrix-*-matrix m n)
(let ((cols (transpose n)))
(map (lambda (x)
(matrix-*-vector cols x))
m)))
gosh> (matrix-*-vector '((1 2)
(3 4))
'(5 6))
(17 39)
gosh> (dot-product '(1 2) '(3 4))
11
gosh> (matrix-*-vector '((1 2)
(3 4))
'(5 6))
(17 39)
gosh> (matrix-*-matrix '((1 2 3)
(4 5 6))
'((7 10)
(8 11)
(9 12)))
((50 68) (122 167))
