edu.usc.ict.iago.utils

Class MathUtils

java.lang.Object

edu.usc.ict.iago.utils.MathUtils

public class MathUtils
extends java.lang.Object

Constructor Summary

Constructors

Constructor and Description
MathUtils()

Method Summary

Modifier and Type	Method and Description
static int[][]	getPermutations(int n) Implements the Steinhaus–Johnson–Trotter algorithm.
static int[][]	getPermutations(int n, int offset) See getPermutations(int).
static int[]	getRandomPermutation(int n) Returns a permutation of n elements in random order.
static <K,V extends java.lang.Comparable<? super V>> java.util.Map<K,V>	sortByValue(java.util.Map<K,V> map) Returns a map that is sorted in descending order by its values.

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

sortByValue

public static <K,V extends java.lang.Comparable<? super V>> java.util.Map<K,V> sortByValue(java.util.Map<K,V> map)

Returns a map that is sorted in descending order by its values. Helpful for looking at Preferences and orderings of points.

Parameters:

map -

Returns:

the sorted map

getRandomPermutation

public static int[] getRandomPermutation(int n)

Returns a permutation of n elements in random order.

Parameters:

n - number of elements

Returns:

random permutation

getPermutations

public static int[][] getPermutations(int n)

Implements the Steinhaus–Johnson–Trotter algorithm. Uses primitive types due to performance considerations. The internal methods used here silently agree that e.g. the work and dir arrays are the same size thus minimizing any sanity checks in the code. Since the factorial of n yields large numbers even for small values of n one should make sure not to pass arbitrarily large numbers for n to this method: at best it simply causes an OutOfMemoryError or may run for a long time.

Parameters:

n - number of elements

Returns:

permutations

getPermutations

public static int[][] getPermutations(int n,
                                      int offset)

See getPermutations(int).

Parameters:

n - number of elements

offset - elements are initialized with this offset

Returns:

permutations