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Moved binomial to separate number-theory file.

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This commit is contained in:
Jens Axel Søgaard 2012-07-03 13:23:44 +02:00
parent 15752bf7b4
commit e6497178e3
2 changed files with 34 additions and 20 deletions
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23
bracket/bracket.rkt
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@ -55,24 +55,7 @@
(module number-theory racket/base
(provide binomial)
; binomial : natural natural -> natural
; compute the binomial coeffecient n choose k
(define (binomial n k)
; <http://www.swox.com/gmp/manual/Binomial-Coefficients-Algorithm.html>
; http://lavica.fesb.hr/cgi-bin/info2html?(gmp)Binomial%20Coefficients%20Algorithm
; TODO: Check range of n and k
(cond
[(= k 0) 1]
[(= k 1) n]
[(= k 2) (/ (* n (- n 1)) 2)]
[(> k (/ n 2)) (binomial n (- n k))]
[else (* (+ n (- k) 1)
(for/product ([i (in-range 2 (+ k 1))])
(/ (+ n (- k) i)
i)))])))
(module undefined racket/base (module undefined racket/base
(provide undefined undefined?) (provide undefined undefined?)
@ -87,6 +70,8 @@
(define (symbolic-id? id) (define (symbolic-id? id)
(or (symbol? id) (or (symbol? id)
(and (syntax? id) (and (syntax? id)
; Syntax symbolical identifiers are not in use.
; Remove this?
(memv (syntax-e id) (memv (syntax-e id)
'(Plus Minus Times Quotient Power =)))))) '(Plus Minus Times Quotient Power =))))))
@ -790,12 +775,12 @@
(module bracket racket (module bracket racket
(require (submod ".." number-theory) (require "../number-theory/number-theory.rkt"
(submod ".." expression) (submod ".." expression)
(submod ".." undefined) (submod ".." undefined)
(submod ".." equation-expression) (submod ".." equation-expression)
"graphics.rkt") "graphics.rkt")
(provide ; (all-from-out (submod ".." symbolic-application)) (provide
(rename-out [free-of Free-of] (rename-out [free-of Free-of]
[base Base] [base Base]
[const Const] [const Const]

29
number-theory/number-theory.rkt Normal file
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@ -0,0 +1,29 @@
#lang racket/base
(provide binomial)
; binomial : natural natural -> natural
; compute the binomial coeffecient n choose k
(define (binomial n k)
; <http://www.swox.com/gmp/manual/Binomial-Coefficients-Algorithm.html>
; http://lavica.fesb.hr/cgi-bin/info2html?(gmp)Binomial%20Coefficients%20Algorithm
; TODO: Check range of n and k
(cond
[(= k 0) 1]
[(= k 1) n]
[(= k 2) (/ (* n (- n 1)) 2)]
[(> k (/ n 2)) (binomial n (- n k))]
[else (* (+ n (- k) 1)
(for/product ([i (in-range 2 (+ k 1))])
(/ (+ n (- k) i)
i)))]))
(module* test #f
(require rackunit)
; Binomial
(check-equal? (binomial 5 0) 1)
(check-equal? (binomial 5 1) 5)
(check-equal? (binomial 5 2) 10)
(check-equal? (binomial 5 3) 10)
(check-equal? (binomial 5 4) 5)
(check-equal? (binomial 5 5) 1)
(check-equal? (binomial 10 6) 210))