org.apache.lucene.util

Class MathUtil

java.lang.Object

org.apache.lucene.util.MathUtil

public final class MathUtil
extends Object

Math static utility methods.

Method Summary

Modifier and Type	Method and Description
static double	acosh(double a) Calculates inverse hyperbolic cosine of a double value.
static double	asinh(double a) Calculates inverse hyperbolic sine of a double value.
static double	atanh(double a) Calculates inverse hyperbolic tangent of a double value.
static long	gcd(long a, long b) Return the greatest common divisor of a and b, consistently with BigInteger.gcd(BigInteger).
static double	log(double base, double x) Calculates logarithm in a given base with doubles.
static int	log(long x, int base) Returns x <= 0 ? 0 : Math.floor(Math.log(x) / Math.log(base))
static double	sumRelativeErrorBound(int numValues) Return a relative error bound for a sum of numValues positive doubles, computed using recursive summation, ie.

Methods inherited from class java.lang.Object

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

Method Detail

log

public static int log(long x,
                      int base)

Returns x <= 0 ? 0 : Math.floor(Math.log(x) / Math.log(base))

Parameters:

base - must be > 1

log

public static double log(double base,
                         double x)

Calculates logarithm in a given base with doubles.

gcd

public static long gcd(long a,
                       long b)

Return the greatest common divisor of a and b, consistently with BigInteger.gcd(BigInteger).

NOTE: A greatest common divisor must be positive, but 2^64 cannot be expressed as a long although it is the GCD of Long.MIN_VALUE and 0 and the GCD of Long.MIN_VALUE and Long.MIN_VALUE. So in these 2 cases, and only them, this method will return Long.MIN_VALUE.

asinh

public static double asinh(double a)

Calculates inverse hyperbolic sine of a double value.

Special cases:

• If the argument is NaN, then the result is NaN.
• If the argument is zero, then the result is a zero with the same sign as the argument.
• If the argument is infinite, then the result is infinity with the same sign as the argument.

acosh

public static double acosh(double a)

Calculates inverse hyperbolic cosine of a double value.

Special cases:

• If the argument is NaN, then the result is NaN.
• If the argument is +1, then the result is a zero.
• If the argument is positive infinity, then the result is positive infinity.
• If the argument is less than 1, then the result is NaN.

atanh

public static double atanh(double a)

Calculates inverse hyperbolic tangent of a double value.

Special cases:

• If the argument is NaN, then the result is NaN.
• If the argument is zero, then the result is a zero with the same sign as the argument.
• If the argument is +1, then the result is positive infinity.
• If the argument is -1, then the result is negative infinity.
• If the argument's absolute value is greater than 1, then the result is NaN.

sumRelativeErrorBound

public static double sumRelativeErrorBound(int numValues)

Return a relative error bound for a sum of numValues positive doubles, computed using recursive summation, ie. sum = x1 + ... + xn. NOTE: This only works if all values are POSITIVE so that Σ |xi| == |Σ xi|. This uses formula 3.5 from Higham, Nicholas J. (1993), "The accuracy of floating point summation", SIAM Journal on Scientific Computing.