datafu.pig.hash.lsh.p_stable

Class L2LSH

java.lang.Object

datafu.pig.hash.lsh.interfaces.LSH

datafu.pig.hash.lsh.p_stable.AbstractStableDistributionFunction

datafu.pig.hash.lsh.p_stable.L2LSH

All Implemented Interfaces:

Sampler

public class L2LSH
extends AbstractStableDistributionFunction
implements Sampler

A locality sensitive hash associated with the L2 metric. This uses a 2-stable distribution to construct the hash.

Field Summary

Fields inherited from class datafu.pig.hash.lsh.interfaces.LSH

dim, rg

Constructor Summary

Constructors

Constructor and Description
L2LSH(int dim, double w, org.apache.commons.math.random.RandomGenerator rand) Constructs a new instance.

Method Summary

Modifier and Type	Method and Description
protected Sampler	getSampler() The sampler determines the metric which this LSH is associated with.
double	sample(org.apache.commons.math.random.RandomDataImpl randomData) Draw a sample s ~ Gaussian(0,1), which is 2-stable.

Methods inherited from class datafu.pig.hash.lsh.p_stable.AbstractStableDistributionFunction

apply, reset

Methods inherited from class datafu.pig.hash.lsh.interfaces.LSH

getDim, getRandomGenerator

Methods inherited from class java.lang.Object

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

Constructor Detail

L2LSH

public L2LSH(int dim,
             double w,
             org.apache.commons.math.random.RandomGenerator rand)
      throws org.apache.commons.math.MathException

Constructs a new instance.

Parameters:

dim - the dimension of the vectors to be hashed

w - a double representing the quantization parameter (also known as the projection width)

rand - the random generator

Throws:

org.apache.commons.math.MathException - MathException

Method Detail

sample

public double sample(org.apache.commons.math.random.RandomDataImpl randomData)

Draw a sample s ~ Gaussian(0,1), which is 2-stable.

Specified by:

sample in interface Sampler

Parameters:

randomData - random data generator

Returns:

a sample from a Gaussian distribution with mu of 0 and sigma of 1

getSampler

protected Sampler getSampler()

Description copied from class: AbstractStableDistributionFunction

The sampler determines the metric which this LSH is associated with. A 1-stable sample will yield a LSH which corresponds to a L1 metric; likewise for 2-stable and L2.

Specified by:

getSampler in class AbstractStableDistributionFunction

Returns:

The sampler to use.