Repository: commons-rng Updated Branches: refs/heads/master 1b0e32ec0 -> 410f2d4b7
Named constants. Project: http://git-wip-us.apache.org/repos/asf/commons-rng/repo Commit: http://git-wip-us.apache.org/repos/asf/commons-rng/commit/410f2d4b Tree: http://git-wip-us.apache.org/repos/asf/commons-rng/tree/410f2d4b Diff: http://git-wip-us.apache.org/repos/asf/commons-rng/diff/410f2d4b Branch: refs/heads/master Commit: 410f2d4b7dd224d8e1a42ce12652fbc68f02814a Parents: 1b0e32e Author: Gilles <er...@apache.org> Authored: Sun Feb 25 17:15:06 2018 +0100 Committer: Gilles <er...@apache.org> Committed: Sun Feb 25 17:15:06 2018 +0100 ---------------------------------------------------------------------- .../RejectionInversionZipfSampler.java | 22 +++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/commons-rng/blob/410f2d4b/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 90ef8b9..d8eafb2 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 @@ -27,6 +27,14 @@ import org.apache.commons.rng.UniformRandomProvider; public class RejectionInversionZipfSampler extends SamplerBase implements DiscreteSampler { + /** Threshold below which Taylor series will be used. */ + private static final double TAYLOR_THRESHOLD = 1e-8; + /** 1/2 */ + private static final double F_1_2 = 0.5; + /** 1/3 */ + private static final double F_1_3 = 1d / 3; + /** 1/4 */ + private static final double F_1_4 = 0.25; /** Number of elements. */ private final int numberOfElements; /** Exponent parameter of the distribution. */ @@ -59,7 +67,7 @@ public class RejectionInversionZipfSampler this.numberOfElements = numberOfElements; this.exponent = exponent; this.hIntegralX1 = hIntegral(1.5) - 1; - this.hIntegralNumberOfElements = hIntegral(numberOfElements + 0.5); + this.hIntegralNumberOfElements = hIntegral(numberOfElements + F_1_2); this.s = 2 - hIntegralInverse(hIntegral(2.5) - h(2)); } @@ -98,7 +106,7 @@ public class RejectionInversionZipfSampler // u is uniformly distributed in (hIntegralX1, hIntegralNumberOfElements] double x = hIntegralInverse(u); - int k = (int) (x + 0.5); + int k = (int) (x + F_1_2); // Limit k to the range [1, numberOfElements] if it would be outside // due to numerical inaccuracies. @@ -115,7 +123,7 @@ public class RejectionInversionZipfSampler // // where C = 1 / (hIntegralNumberOfElements - hIntegralX1) - if (k - x <= s || u >= hIntegral(k + 0.5) - h(k)) { + if (k - x <= s || u >= hIntegral(k + F_1_2) - h(k)) { // Case k = 1: // @@ -216,10 +224,10 @@ public class RejectionInversionZipfSampler * @return {@code log(1 + x) / x}. */ private static double helper1(final double x) { - if (Math.abs(x) > 1e-8) { + if (Math.abs(x) > TAYLOR_THRESHOLD) { return Math.log1p(x) / x; } else { - return 1 - x * (0.5 - x * (0.33333333333333333 - 0.25 * x)); + return 1 - x * (F_1_2 - x * (F_1_3 - F_1_4 * x)); } } @@ -233,10 +241,10 @@ public class RejectionInversionZipfSampler * @return {@code (exp(x) - 1) / x} if x is non-zero, or 1 if x = 0. */ private static double helper2(final double x) { - if (Math.abs(x) > 1e-8) { + if (Math.abs(x) > TAYLOR_THRESHOLD) { return Math.expm1(x) / x; } else { - return 1 + x * 0.5 * (1 + x * 0.33333333333333333 * (1 + 0.25 * x)); + return 1 + x * F_1_2 * (1 + x * F_1_3 * (1 + F_1_4 * x)); } } }
