Repository: commons-math Updated Branches: refs/heads/master 002276ea3 -> bd5afc0b5
[MATH-1221] Improve performance of ZipfDistribution by caching the nth generalized harmonic. Project: http://git-wip-us.apache.org/repos/asf/commons-math/repo Commit: http://git-wip-us.apache.org/repos/asf/commons-math/commit/bd5afc0b Tree: http://git-wip-us.apache.org/repos/asf/commons-math/tree/bd5afc0b Diff: http://git-wip-us.apache.org/repos/asf/commons-math/diff/bd5afc0b Branch: refs/heads/master Commit: bd5afc0b5a977c168cf046e3244477b48fa72c5d Parents: 002276e Author: Thomas Neidhart <thomas.neidh...@gmail.com> Authored: Fri May 1 14:12:44 2015 +0200 Committer: Thomas Neidhart <thomas.neidh...@gmail.com> Committed: Fri May 1 14:12:44 2015 +0200 ---------------------------------------------------------------------- src/changes/changes.xml | 3 +++ .../commons/math4/distribution/ZipfDistribution.java | 15 +++++++++------ 2 files changed, 12 insertions(+), 6 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/commons-math/blob/bd5afc0b/src/changes/changes.xml ---------------------------------------------------------------------- diff --git a/src/changes/changes.xml b/src/changes/changes.xml index 1fb151f..649258f 100644 --- a/src/changes/changes.xml +++ b/src/changes/changes.xml @@ -54,6 +54,9 @@ If the output is not quite correct, check for invisible trailing spaces! </release> <release version="4.0" date="XXXX-XX-XX" description=""> + <action dev="tn" type="fix" issue="MATH-1221"> + Improve performance of "ZipfDistribution" by caching the nth generalized harmonic. + </action> <action dev="tn" type="fix" issue="MATH-1220" due-to="Otmar Ertl"> <!-- backported to 3.6 --> Improve performance of "ZipfDistribution#sample()" by using a rejection algorithm. </action> http://git-wip-us.apache.org/repos/asf/commons-math/blob/bd5afc0b/src/main/java/org/apache/commons/math4/distribution/ZipfDistribution.java ---------------------------------------------------------------------- diff --git a/src/main/java/org/apache/commons/math4/distribution/ZipfDistribution.java b/src/main/java/org/apache/commons/math4/distribution/ZipfDistribution.java index 366af69..0e54e76 100644 --- a/src/main/java/org/apache/commons/math4/distribution/ZipfDistribution.java +++ b/src/main/java/org/apache/commons/math4/distribution/ZipfDistribution.java @@ -30,11 +30,13 @@ import org.apache.commons.math4.util.FastMath; */ public class ZipfDistribution extends AbstractIntegerDistribution { /** Serializable version identifier. */ - private static final long serialVersionUID = -140627372283420404L; + private static final long serialVersionUID = 20150501L; /** Number of elements. */ private final int numberOfElements; /** Exponent parameter of the distribution. */ private final double exponent; + /** Cached values of the nth generalized harmonic. */ + private final double nthHarmonic; /** Cached numerical mean */ private double numericalMean = Double.NaN; /** Whether or not the numerical mean has been calculated */ @@ -93,6 +95,7 @@ public class ZipfDistribution extends AbstractIntegerDistribution { this.numberOfElements = numberOfElements; this.exponent = exponent; + this.nthHarmonic = generalizedHarmonic(numberOfElements, exponent); } /** @@ -120,7 +123,7 @@ public class ZipfDistribution extends AbstractIntegerDistribution { return 0.0; } - return (1.0 / FastMath.pow(x, exponent)) / generalizedHarmonic(numberOfElements, exponent); + return (1.0 / FastMath.pow(x, exponent)) / nthHarmonic; } /** {@inheritDoc} */ @@ -130,7 +133,7 @@ public class ZipfDistribution extends AbstractIntegerDistribution { return Double.NEGATIVE_INFINITY; } - return -FastMath.log(x) * exponent - FastMath.log(generalizedHarmonic(numberOfElements, exponent)); + return -FastMath.log(x) * exponent - FastMath.log(nthHarmonic); } /** {@inheritDoc} */ @@ -142,7 +145,7 @@ public class ZipfDistribution extends AbstractIntegerDistribution { return 1.0; } - return generalizedHarmonic(x, exponent) / generalizedHarmonic(numberOfElements, exponent); + return generalizedHarmonic(x, exponent) / nthHarmonic; } /** @@ -174,7 +177,7 @@ public class ZipfDistribution extends AbstractIntegerDistribution { final double s = getExponent(); final double Hs1 = generalizedHarmonic(N, s - 1); - final double Hs = generalizedHarmonic(N, s); + final double Hs = nthHarmonic; return Hs1 / Hs; } @@ -210,7 +213,7 @@ public class ZipfDistribution extends AbstractIntegerDistribution { final double Hs2 = generalizedHarmonic(N, s - 2); final double Hs1 = generalizedHarmonic(N, s - 1); - final double Hs = generalizedHarmonic(N, s); + final double Hs = nthHarmonic; return (Hs2 / Hs) - ((Hs1 * Hs1) / (Hs * Hs)); }
