org.openimaj.math.util

Class MathUtils

java.lang.Object

org.openimaj.math.util.MathUtils

public class MathUtils
extends Object

A collection of maths functions not available anywhere else ive seen

Author:

Sina Samangooei (ss@ecs.soton.ac.uk)

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	MathUtils.ExponentAndMantissa Class to hold an exponent and mantissa

Constructor Summary

Constructors

Constructor and Description
MathUtils()

Method Summary

Modifier and Type	Method and Description
static MathUtils.ExponentAndMantissa	frexp(double value) Implementation of the C frexp function to break floating-point number into normalized fraction and power of 2.
static double	logSum(double log_a, double log_b) Given log(a) and log(b) calculate log(a + b) boils down to log( exp(log_a) + exp(log_b) ) but this might overflow, so we turn this into log([exp(log_a - log_c) + exp(log_b - log_c)]exp(log_c)) and we set log_c == max(log_a,log_b) and so it becomes: LARGE + log(1 + exp(SMALL - LARGE)) == LARGE + log(1 + SMALL) ~= large the whole idea being to avoid an overflow (exp(LARGE) == VERY LARGE == overflow)
static int	nextPowerOf2(int n) Returns the next power of 2 superior to n.

Methods inherited from class java.lang.Object

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

Constructor Detail

MathUtils

public MathUtils()

Method Detail

logSum

public static double logSum(double log_a,
                            double log_b)

Given log(a) and log(b) calculate log(a + b) boils down to log( exp(log_a) + exp(log_b) ) but this might overflow, so we turn this into log([exp(log_a - log_c) + exp(log_b - log_c)]exp(log_c)) and we set log_c == max(log_a,log_b) and so it becomes: LARGE + log(1 + exp(SMALL - LARGE)) == LARGE + log(1 + SMALL) ~= large the whole idea being to avoid an overflow (exp(LARGE) == VERY LARGE == overflow)

Parameters:

log_a -

log_b -

Returns:

log(a+b)

nextPowerOf2

public static int nextPowerOf2(int n)

Returns the next power of 2 superior to n.

Parameters:

n - The value to find the next power of 2 above

Returns:

The next power of 2

frexp

public static MathUtils.ExponentAndMantissa frexp(double value)

Implementation of the C frexp function to break floating-point number into normalized fraction and power of 2.

Parameters:

value - the value

Returns:

the exponent and mantissa of the input value

See Also:

"http://stackoverflow.com/questions/1552738/is-there-a-java-equivalent-of-frexp"