Petar Kapriš
2ca5e73a27
Notes: The exercise 2.37 on Hexlet's site has an error, noted in the comments. Also, their page for exercise 2.38 should probably have 0 tests. And finally, I did not calculate the exact number in the final exercise 2.43, but I included a relevant discussion.
36 lines
838 B
Scheme
36 lines
838 B
Scheme
#lang sicp
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;;;;
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;; Error in the hexlet exercise: the matrix-*-vector line should say
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;; m_ij*v_j not m_ij*v_i
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;;;;
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(define (accumulate op initial sequence)
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(if (null? sequence)
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initial
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(op (car sequence)
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(accumulate op initial (cdr sequence)))))
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(define (accumulate-n op init seqs)
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(if (null? (car seqs))
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'()
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(cons (accumulate op init (map car seqs))
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(accumulate-n op init (map cdr seqs)))))
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(define (dot-product v w)
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(accumulate + 0 (map * v w)))
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(define (matrix-*-vector m v)
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(map (lambda (row)
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(dot-product row v))
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m))
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(define (matrix-*-matrix m n)
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(let ((cols (transpose n)))
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(map (lambda (row-m)
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(map (lambda (col)
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(dot-product row-m col))
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cols))
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m)))
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(define (transpose m)
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(accumulate-n cons '() m))
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