Package edu.cmu.tetrad.util

Class ChoiceGenerator

java.lang.Object

edu.cmu.tetrad.util.ChoiceGenerator

public final class ChoiceGenerator
extends Object

Generates (nonrecursively) all of the combinations of a choose b, where a, b are nonnegative integers and a >= b. The values of a and b are given in the constructor, and the sequence of choices is obtained by repeatedly calling the next() method. When the sequence is finished, null is returned.

A valid combination for the sequence of combinations for a choose b generated by this class is an array x[] of b integers i, 0 <= i < a, such that x[j] < x[j + 1] for each j from 0 to b - 1.

To see what this class does, try calling ChoiceGenerator.testPrint(5, 3), for instance.

Version:

$Id: $Id

Author:

josephramsey

Constructor Summary

Constructors

Constructor	Description
ChoiceGenerator(int a, int b)	Constructs a new choice generator for a choose b.

Method Summary

Modifier and Type	Method	Description
int	getA()	Getter for the field a.
int	getB()	Getter for the field b.
static int	getNumCombinations(int a, int b)	Returns the number of combinations of a choose b.
static double	logCombinations(int a, int b)	Returns the natural logarithm of the number of combinations of a choose b.
int[]	next()	next.
static void	testPrint(int a, int b)	This static method will print the series of combinations for a choose b to System.out.

Methods inherited from class java.lang.Object

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

Constructor Details

ChoiceGenerator

public ChoiceGenerator(int a,
 int b)

Constructs a new choice generator for a choose b. Once this initialization has been performed, successive calls to next() will produce the series of combinations. To begin a new series at any time, call this init method again with new values for a and b.

Parameters:

a - the number of objects being selected from.

b - the number of objects in the desired selection.

Method Details

testPrint

public static void testPrint(int a,
 int b)

This static method will print the series of combinations for a choose b to System.out.

Parameters:

a - the number of objects being selected from.

b - the number of objects in the desired selection.

getNumCombinations

public static int getNumCombinations(int a,
 int b)

Returns the number of combinations of a choose b.

Parameters:

a - the number of objects being selected from.

b - the number of objects in the desired selection.

Returns:

the number of combinations of a choose b.

logCombinations

public static double logCombinations(int a,
 int b)

Returns the natural logarithm of the number of combinations of a choose b.

Parameters:

a - the number of objects being selected from.

b - the number of objects in the desired selection.

Returns:

the natural logarithm of the number of combinations of a choose b.

next

public int[] next()

next.

Returns:

the next combination in the series, or null if the series is finished.

getA

public int getA()

Getter for the field a.

Returns:

Ibid.

getB

public int getB()

Getter for the field b.

Returns:

Ibid.