;;; PLT Scheme Science Collection ;;; random-distributions/flat.ss ;;; Copyright (c) 2004-2007 M. Douglas Williams ;;; ;;; This library is free software; you can redistribute it and/or ;;; modify it under the terms of the GNU Lesser General Public ;;; License as published by the Free Software Foundation; either ;;; version 2.1 of the License, or (at your option) any later version. ;;; ;;; This library is distributed in the hope that it will be useful, ;;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU ;;; Lesser General Public License for more details. ;;; ;;; You should have received a copy of the GNU Lesser General Public ;;; License along with this library; if not, write to the Free ;;; Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA ;;; 02111-1307 USA. ;;; ;;; ------------------------------------------------------------------- ;;; ;;; This code implements a flat (uniform) distribution. It is based on ;;; the Random Number Distributions in the GNU Scientific Library. ;;; ;;; Version Date Description ;;; 0.9.0 08/06/04 This is the initial release of the flat ;;; distribution routines. (Doug Williams) ;;; 1.0.0 09/28/04 Marked as ready for Release 1.0. Added ;;; contracts for functions. (Doug Williams) ;;; 2.0.0 11/19/07 Added unchecked versions of functions and ;;; getting ready for PLT Scheme 4.0 (Doug Williams) (module flat mzscheme (require (lib "contract.ss")) (provide (rename random-flat unchecked-random-flat) (rename flat-pdf unchecked-flat-pdf) (rename flat-cdf unchecked-flat-cdf)) (provide/contract (random-flat (case-> (->r ((r random-source?) (a real?) (b (>/c a))) real?) (->r ((a real?) (b (>/c a))) real?))) (flat-pdf (->r ((x real?) (a real?) (b (>/c a))) (>=/c 0.0))) (flat-cdf (->r ((x real?) (a real?) (b (>=/c a))) (real-in 0.0 1.0)))) (require "../random-source.ss") ;; random-flat: random-source x real x real -> real ;; random-flat: real x real -> real ;; ;; This function returns a random variate from the flat (uniform) ;; distribution from a to b. (define random-flat (case-lambda ((r a b) (let ((u (unchecked-random-uniform r))) (+ (* a (- 1 u)) (* b u)))) ((a b) (random-flat (current-random-source) a b)))) ;; flat-pdf: real x real x real-> real ;; ;; This function computes the probability density p(x) at x for a ;; flat (uniform) distribution from a to b. (define (flat-pdf x a b) (if (< x a) ;; x < a 0 (if (<= x b) ;; a <= x <= b (/ 1.0 (- b a)) ;; x > b 0))) ;; flat-cdf: real x real x real-> real ;; ;; This function computes the cummulative density d(x) at x for a ;; flat (uniform) distribution from a to b. (define (flat-cdf x a b) (if (< x a) ;; x < a 0 (if (<= x b) ;; a <= x <= c (/ (- x a) (- b a)) ;; x > b 1))) )