com.tdunning.math.stats

Class LogHistogram

java.lang.Object

com.tdunning.math.stats.Histogram

com.tdunning.math.stats.LogHistogram

All Implemented Interfaces:

Serializable

public class LogHistogram
extends Histogram

Non-linear histogram that uses floating point representation plus a quadratic correction to bin width to achieve tighter fit to the ideal log2 sizing.

See Also:

Serialized Form

Field Summary

Fields inherited from class com.tdunning.math.stats.Histogram

counts, max, min

Constructor Summary

Constructors

Constructor and Description
LogHistogram(double min, double max)
LogHistogram(double min, double max, double epsilonFactor)

Method Summary

Modifier and Type	Method and Description
static double	approxLog2(double value) Approximates log_2(value) by abusing floating point hardware.
protected int	bucketIndex(double x)
static double	pow2(double x) Computes an approximate value of 2^x.

Methods inherited from class com.tdunning.math.stats.Histogram

add, getBounds, getCounts, setupBins

Methods inherited from class java.lang.Object

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

Constructor Detail

LogHistogram

public LogHistogram(double min,
                    double max)

LogHistogram

public LogHistogram(double min,
                    double max,
                    double epsilonFactor)

Method Detail

approxLog2

public static double approxLog2(double value)

Approximates log_2(value) by abusing floating point hardware. The floating point exponent is used to get the integer part of the log. The mantissa is then adjusted with a second order polynomial to get a better approximation. The error is bounded to be less than ±0.01 and is zero at every power of two (which also implies the approximation is continuous).

Parameters:

value - The argument of the log

Returns:

log_2(value) (within an error of about ± 0.01)

pow2

public static double pow2(double x)

Computes an approximate value of 2^x. This is done as an exact inverse of #approxLog2 so that bin boundaries can be computed exactly.

Parameters:

x - The power of 2 desired.

Returns:

2^x approximately.

bucketIndex

protected int bucketIndex(double x)

Specified by:

bucketIndex in class Histogram