org.apache.mahout.math.jet.math

Class Arithmetic

java.lang.Object

org.apache.mahout.math.jet.math.Arithmetic

public final class Arithmetic
extends Object

Arithmetic functions.

Method Summary

Methods

Modifier and Type	Method and Description
static double	binomial(long n, long k) Efficiently returns the binomial coefficient, often also referred to as "n over k" or "n choose k".
static double	logFactorial(int k) Returns log(k!).

Methods inherited from class java.lang.Object

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

Method Detail

binomial

public static double binomial(long n,
              long k)

Efficiently returns the binomial coefficient, often also referred to as "n over k" or "n choose k". The binomial coefficient is defined as

• k<0: 0.
• k==0 || k==n: 1.
• k==1 || k==n-1: n.
• else: (n * n-1 * ... * n-k+1 ) / ( 1 * 2 * ... * k ).

Returns:

the binomial coefficient.

logFactorial

public static double logFactorial(int k)

Returns log(k!). Tries to avoid overflows. For k<30 simply looks up a table in O(1). For k>=30 uses stirlings approximation.

Parameters:

k - must hold k >= 0.