Package 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
  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.
  `static double`
  `sumUpperBound(double sum, int numValues)`
  Return the maximum possible sum across `numValues` non-negative doubles, assuming one sum yielded `sum`.
  `static int`
  `unsignedMin(int a, int b)`
  Return the min of the two given unsigned integers.

  ### Methods inherited from class java.lang.Object

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

- ## Method Details

  - ### 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.

  - ### sumUpperBound

    public static double sumUpperBound(double sum, int numValues)
    Return the maximum possible sum across `numValues` non-negative doubles, assuming one sum yielded `sum`.
    See Also:
      - `sumRelativeErrorBound(int)`

  - ### unsignedMin

    public static int unsignedMin(int a, int b)
    Return the min of the two given unsigned integers.