Author: fanningpj
Date: Sun Jun 5 09:49:10 2022
New Revision: 1901661
URL: http://svn.apache.org/viewvc?rev=1901661&view=rev
Log:
use commons-math3 for poisson dist
Modified:
poi/trunk/poi/src/main/java/org/apache/poi/ss/formula/functions/Poisson.java
Modified:
poi/trunk/poi/src/main/java/org/apache/poi/ss/formula/functions/Poisson.java
URL:
http://svn.apache.org/viewvc/poi/trunk/poi/src/main/java/org/apache/poi/ss/formula/functions/Poisson.java?rev=1901661&r1=1901660&r2=1901661&view=diff
==============================================================================
---
poi/trunk/poi/src/main/java/org/apache/poi/ss/formula/functions/Poisson.java
(original)
+++
poi/trunk/poi/src/main/java/org/apache/poi/ss/formula/functions/Poisson.java
Sun Jun 5 09:49:10 2022
@@ -17,6 +17,7 @@
package org.apache.poi.ss.formula.functions;
+import org.apache.commons.math3.distribution.PoissonDistribution;
import org.apache.poi.ss.formula.OperationEvaluationContext;
import org.apache.poi.ss.formula.eval.BoolEval;
import org.apache.poi.ss.formula.eval.ErrorEval;
@@ -30,16 +31,6 @@ public class Poisson implements FreeRefF
private static final double DEFAULT_RETURN_RESULT = 1;
- /** All long-representable factorials */
- private static final long[] FACTORIALS = {
- 1L, 1L, 2L,
- 6L, 24L, 120L,
- 720L, 5040L, 40320L,
- 362880L, 3628800L, 39916800L,
- 479001600L, 6227020800L, 87178291200L,
- 1307674368000L, 20922789888000L, 355687428096000L,
- 6402373705728000L, 121645100408832000L, 2432902008176640000L };
-
/**
* This checks is x = 0 and the mean = 0.
* Excel currently returns the value 1 where as the
@@ -61,25 +52,6 @@ public class Poisson implements FreeRefF
}
}
- private static double probability(int k, double lambda) {
- return Math.pow(lambda, k) * Math.exp(-lambda) / factorial(k);
- }
-
- private static double cumulativeProbability(int x, double lambda) {
- double result = 0;
- for(int k = 0; k <= x; k++){
- result += probability(k, lambda);
- }
- return result;
- }
-
- private static long factorial(final int n) {
- if (n < 0 || n > 20) {
- throw new IllegalArgumentException("Valid argument should be in
the range [0..20]");
- }
- return FACTORIALS[n];
- }
-
@Override
public ValueEval evaluate(ValueEval[] args, OperationEvaluationContext ec)
{
return evaluate(args, ec.getRowIndex(), ec.getColumnIndex());
@@ -114,7 +86,10 @@ public class Poisson implements FreeRefF
// truncate x : as per excel function def
boolean cumulative = ((BoolEval)arg2).getBooleanValue();
- double result = cumulative ? cumulativeProbability((int) x, mean)
: probability((int) x, mean);
+ PoissonDistribution poissonDistribution = new
PoissonDistribution(mean);
+ double result = cumulative ?
+ poissonDistribution.cumulativeProbability((int) x) :
+ poissonDistribution.probability((int) x);
// check the result
NumericFunction.checkValue(result);
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