jdd.util.math

Class Chi2Test

java.lang.Object

jdd.util.math.Chi2Test

public class Chi2Test
extends Object

\chi^2 random distribution test.

This class is used to test the distribution of series of numbers such hashes and (pseudo) random numbers.

assume that you want to test a function f() which returns a number between 0 and N-1:

 Chi2Test  c2t = new Chi2Test(N);

 while(c2t.more()) c2t.add( f() );

 if(c2t.isChi2Acceptable())
    System.out.println("The distribution of f() is random enough for me!");
 

Constructor Summary

Constructors

Constructor and Description
Chi2Test(int n) start a chi^2 for the input numbers 0..n-1

Method Summary

Modifier and Type	Method and Description
void	add(int x) add a new number.
double	getChi2() get the chi2 value.
int[]	getDistibution() Get the distribution vector
double	getStandardDeviation() get the standard deviation.
boolean	isChi2Acceptable() "Acceptable" does not mean good.
boolean	isStandardDeviationAcceptable() "Acceptable" does not mean good.
static void	main(String[] args)
boolean	more() returns true if it has enough samples to give an accurate answer.
void	reset() reset the chi^2, start all over

Methods inherited from class java.lang.Object

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

Constructor Detail

Chi2Test

public Chi2Test(int n)

start a chi^2 for the input numbers 0..n-1

n must be larger than 20. don't make it too large unless you have enough memory for it.

Also, if n is too small (say bellow 1000), then you might get many false answers so instead consider the majority of multiple runs.

Method Detail

reset

public void reset()

reset the chi^2, start all over

more

public boolean more()

returns true if it has enough samples to give an accurate answer.

NOTE: most other functions here cannot be called before this functions starts returning falsees!

add

public void add(int x)

add a new number. you now you have fed it enough numbers when more() returns false.

See Also:

more()

getChi2

public double getChi2()

get the chi2 value. do not call before more() has returned true!

getStandardDeviation

public double getStandardDeviation()

get the standard deviation. do not call before more() has returned true!

isChi2Acceptable

public boolean isChi2Acceptable()

"Acceptable" does not mean good. For example, for hash functions, acceptable means very good. So don't take it as a hard limit, it sometimes fails so do multiple runs,

Returns:

true if the current chi2 value is acceptable

See Also:

isStandardDeviationAcceptable(), getChi2()

isStandardDeviationAcceptable

public boolean isStandardDeviationAcceptable()

"Acceptable" does not mean good. For example, for hash functions, acceptable means very good. So don't take it as a hard limit, it sometimes fails so do multiple runs,

Returns:

true if the current standard deviation is acceptable.

See Also:

isChi2Acceptable(), getStandardDeviation()

getDistibution

public int[] getDistibution()

Get the distribution vector

main

public static void main(String[] args)