(commons-statistics) branch master updated: Implement the range probability(from, to) using a single sum

[aherbert]

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aherbert pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/commons-statistics.git


The following commit(s) were added to refs/heads/master by this push:
     new 716a4539 Implement the range probability(from, to) using a single sum
716a4539 is described below

commit 716a4539367956ac216dd459b0847d61a5c027ec
Author: Alex Herbert <aherb...@apache.org>
AuthorDate: Tue Sep 1 18:00:37 2026 +0100

    Implement the range probability(from, to) using a single sum
---
 .../statistics/distribution/ZipfDistribution.java  | 23 ++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git 
a/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/ZipfDistribution.java
 
b/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/ZipfDistribution.java
index 315e76c8..713bba40 100644
--- 
a/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/ZipfDistribution.java
+++ 
b/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/ZipfDistribution.java
@@ -132,6 +132,29 @@ public final class ZipfDistribution extends 
AbstractDiscreteDistribution {
         return Math.pow(x, -exponent) / nthHarmonic;
     }
 
+    /** {@inheritDoc} */
+    @Override
+    public double probability(int x0,
+                              int x1) {
+        if (x0 > x1) {
+            throw new 
DistributionException(DistributionException.INVALID_RANGE_LOW_GT_HIGH, x0, x1);
+        }
+        if (x0 == x1 || x1 < 1) {
+            // (x0, x1] does not overlap [1, n]
+            return 0;
+        }
+        // If the range is outside the bounds use the appropriate cumulative 
probability
+        if (x0 < 1) {
+            return cumulativeProbability(x1);
+        }
+        if (x1 >= numberOfElements) {
+            return survivalProbability(x0);
+        }
+        // Here: 1 <= x0 < x1 < n:
+        // sum(pdf(x)) for x in (x0, x1]
+        return generalizedHarmonic(x0 + 1, x1, exponent) / nthHarmonic;
+    }
+
     /** {@inheritDoc} */
     @Override
     public double logProbability(int x) {