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

    All Methods Static Methods Concrete Methods
    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.

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