Package org.apache.commons.math4.util

Class CombinatoricsUtils

java.lang.Object

org.apache.commons.math4.util.CombinatoricsUtils

public final class CombinatoricsUtils
extends java.lang.Object

Combinatorial utilities.

Since:

3.3

Method Summary

Modifier and Type	Method	Description
static long	stirlingS2(int n, int k)	Returns the Stirling number of the second kind, "S(n,k)", the number of ways of partitioning an n-element set into k non-empty subsets.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

stirlingS2

public static long stirlingS2(int n,
                              int k)
                       throws NotPositiveException,
                              NumberIsTooLargeException,
                              MathArithmeticException

Returns the Stirling number of the second kind, "S(n,k)", the number of ways of partitioning an n-element set into k non-empty subsets.

The preconditions are 0 <= k <= n (otherwise NotPositiveException is thrown)

Parameters:

n - the size of the set

k - the number of non-empty subsets

Returns:

S(n,k)

Throws:

NotPositiveException - if k < 0.

NumberIsTooLargeException - if k > n.

MathArithmeticException - if some overflow happens, typically for n exceeding 25 and k between 20 and n-2 (S(n,n-1) is handled specifically and does not overflow)

Since:

3.1