f40ad2ca9d
* Fixed type of `matrix-expt' * Made matrix functions respect `array-strictness' parameter (mostly wrapping functions with `parameterize' and return values with `array-default-strictness'; reindentation makes changes look larger) * Added strictness tests
32 lines
1.1 KiB
Racket
32 lines
1.1 KiB
Racket
#lang typed/racket/base
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(require "matrix-types.rkt"
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"matrix-constructors.rkt"
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"matrix-arithmetic.rkt"
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"utils.rkt")
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(provide matrix-expt)
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(: matrix-expt/ns (case-> ((Matrix Real) Positive-Integer -> (Matrix Real))
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((Matrix Number) Positive-Integer -> (Matrix Number))))
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(define (matrix-expt/ns a n)
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(define n/2 (quotient n 2))
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(if (zero? n/2)
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;; n = 1
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a
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(let ([m (* n/2 2)])
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(if (= n m)
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;; n is even
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(let ([a^n/2 (matrix-expt/ns a n/2)])
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(matrix* a^n/2 a^n/2))
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;; m = n - 1
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(matrix* a (matrix-expt/ns a m))))))
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(: matrix-expt (case-> ((Matrix Real) Integer -> (Matrix Real))
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((Matrix Number) Integer -> (Matrix Number))))
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(define (matrix-expt a n)
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(cond [(not (square-matrix? a)) (raise-argument-error 'matrix-expt "square-matrix?" 0 a n)]
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[(negative? n) (raise-argument-error 'matrix-expt "Natural" 1 a n)]
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[(zero? n) (identity-matrix (square-matrix-size a))]
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[else (call/ns (λ () (matrix-expt/ns a n)))]))
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