org.apache.commons.numbers.combinatorics

Class FactorialDouble

java.lang.Object

org.apache.commons.numbers.combinatorics.FactorialDouble

public final class FactorialDouble
extends Object

Class for computing the natural logarithm of the factorial of a number. It allows to allocate a cache of precomputed values.

Method Summary

Modifier and Type	Method and Description
static FactorialDouble	create() Creates an instance with no precomputed values.
double	value(int n) Computes the factorial of n.
FactorialDouble	withCache(int cacheSize) Creates an instance with the specified cache size.

Methods inherited from class java.lang.Object

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

Method Detail

create

public static FactorialDouble create()

Creates an instance with no precomputed values.

Returns:

instance with no precomputed values

withCache

public FactorialDouble withCache(int cacheSize)

Creates an instance with the specified cache size.

Parameters:

cacheSize - Number of precomputed values of the function.

Returns:

a new instance where cacheSize values have been precomputed.

Throws:

IllegalArgumentException - if cacheSize < 0.

value

public double value(int n)

Computes the factorial of n. The result should be small enough to fit into a double: The largest n for which n! does not exceed Double.MAX_VALUE is 170. Double.POSITIVE_INFINITY is returned for n > 170.

Parameters:

n - Argument.

Returns:

n!

Throws:

IllegalArgumentException - if n < 0.