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Project: http://git-wip-us.apache.org/repos/asf/commons-rng/repo Commit: http://git-wip-us.apache.org/repos/asf/commons-rng/commit/525686df Tree: http://git-wip-us.apache.org/repos/asf/commons-rng/tree/525686df Diff: http://git-wip-us.apache.org/repos/asf/commons-rng/diff/525686df Branch: refs/heads/master Commit: 525686dffd5fb9874ab6ab6ed6a0da89cd38cff9 Parents: 886a71f Author: Gilles <er...@apache.org> Authored: Thu Nov 17 14:20:37 2016 +0100 Committer: Gilles <er...@apache.org> Committed: Thu Nov 17 14:20:37 2016 +0100 ---------------------------------------------------------------------- .../RejectionInversionZipfSampler.java | 51 +++++++++----------- 1 file changed, 24 insertions(+), 27 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/commons-rng/blob/525686df/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/distribution/RejectionInversionZipfSampler.java ---------------------------------------------------------------------- diff --git a/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/distribution/RejectionInversionZipfSampler.java b/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/distribution/RejectionInversionZipfSampler.java index 02b1ca4..a5bd8c6 100644 --- a/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/distribution/RejectionInversionZipfSampler.java +++ b/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/distribution/RejectionInversionZipfSampler.java @@ -66,36 +66,33 @@ public class RejectionInversionZipfSampler /** * Rejection inversion sampling method for a discrete, bounded Zipf * distribution that is based on the method described in - * <p> - * Wolfgang Hörmann and Gerhard Derflinger - * "Rejection-inversion to generate variates from monotone discrete - * distributions", ACM Transactions on Modeling and Computer Simulation - * (TOMACS) 6.3 (1996): 169-184. - * </p> - * - * <p> - * The paper describes an algorithm for exponents larger than 1 - * (Algorithm ZRI). - * The original method uses {@code H(x) = (v + x)^(1 - q) / (1 - q)} - * as the integral of the hat function. - * This function is undefined for q = 1, which is the reason for - * the limitation of the exponent. - * If instead the integral function - * {@code H(x) = ((v + x)^(1 - q) - 1) / (1 - q)} is used, - * for which a meaningful limit exists for q = 1, the method works - * for all positive exponents. - * </p> - * - * <p> - * The following implementation uses v = 0 and generates integral - * number in the range [1, numberOfElements]. - * This is different to the original method where v is defined to - * be positive and numbers are taken from [0, i_max]. - * This explains why the implementation looks slightly different. - * </p> + * <blockquote> + * Wolfgang Hörmann and Gerhard Derflinger. + * <i>"Rejection-inversion to generate variates from monotone discrete + * distributions",<i><br> + * <strong>ACM Transactions on Modeling and Computer Simulation</strong> (TOMACS) 6.3 (1996): 169-184. + * </blockquote> */ @Override public int sample() { + // The paper describes an algorithm for exponents larger than 1 + // (Algorithm ZRI). + // The original method uses + // H(x) = (v + x)^(1 - q) / (1 - q) + // as the integral of the hat function. + // This function is undefined for q = 1, which is the reason for + // the limitation of the exponent. + // If instead the integral function + // H(x) = ((v + x)^(1 - q) - 1) / (1 - q) + // is used, + // for which a meaningful limit exists for q = 1, the method works + // for all positive exponents. + // The following implementation uses v = 0 and generates integral + // number in the range [1, numberOfElements]. + // This is different to the original method where v is defined to + // be positive and numbers are taken from [0, i_max]. + // This explains why the implementation looks slightly different. + while(true) { final double u = hIntegralNumberOfElements + nextDouble() * (hIntegralX1 - hIntegralNumberOfElements); // u is uniformly distributed in (hIntegralX1, hIntegralNumberOfElements]
