Hands on the CombinatoricsUtils class in Apache Commons Math

Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!

https://commons.apache.org/proper/commons-math/javadocs/api-3.6/index.html?org/apache/commons/math3/util/CombinatoricsUtils.html

%%classpath add mvn
org.apache.commons commons-math3 3.6.1

import org.apache.commons.math3.util.CombinatoricsUtils._

import org.apache.commons.math3.util.CombinatoricsUtils._

binomialCoefficient¶

binomialCoefficient(5, 3)

10

binomialCoefficientDouble(5, 3)

10.0

binomialCoefficientLog(5, 3)

2.302585092994046

checkBinomial(5, 3)

combinationsIterator¶

Notice that this methods returns an iterator of the type java.util.Iterator[Array[Int]], which is not a Scala Iterator! For combinations/permutations iterator, it is suggested that you use Seq.combinations and/or Seq.permutations.

val it = combinationsIterator(5, 3)

org.apache.commons.math3.util.Combinations$LexicographicIterator@1ab48026

Factorial¶

factorial(10)

3628800

factorial(100)

org.apache.commons.math3.exception.MathArithmeticException: arithmetic exception
  at org.apache.commons.math3.util.CombinatoricsUtils.factorial(CombinatoricsUtils.java:281)
  ... 46 elided

factorialDouble(100)

9.332621544395286E157

factorialDouble(20)

2.43290200817664E18

factorialLog(100)

363.7393755555636

Stirling¶

stirlingS2(10, 3)

9330