Package org.ejml.dense.row.misc

Class PermuteArray

java.lang.Object
org.ejml.dense.row.misc.PermuteArray
public class PermuteArray extends Object
Generates a permutations of an integer set from 0 to N-1. This can either be generated all at once as a list of one at a time.

  • Constructor Summary

    Constructors
    Constructor
    Description
    PermuteArray(int N)
     

  • Method Summary

    Modifier and Type
    Method
    Description
    static List<int[]>
    createList(int N)
    Creates a list of all permutations for a set with N elements.
    static int
    fact(int N)
    Computes N factorial
    @org.jetbrains.annotations.Nullable int[]
    next()
    Creates the next permutation in the sequence.
    int
    sgn()
    Returns signature of the permutation.

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • PermuteArray

      public PermuteArray(int N)

  • Method Details

    • sgn

      public int sgn()

      Returns signature of the permutation. This is the sgn() operator and returns -1 or 1 depending on it being odd or even.
      sgn(σ) = ( − 1)m

      where m is the number of inversions.

      NOTE: This implementation is painfully slow O(N!). There is probably another algorithm out there which is much faster.

      Returns:
      -1 or 1 for odd or even permutations.

    • fact

      public static int fact(int N)
      Computes N factorial

    • createList

      public static List<int[]> createList(int N)
      Creates a list of all permutations for a set with N elements.
      Parameters:
      N - Number of elements in the list being permuted.
      Returns:
      A list containing all the permutations.

    • next

      @Nullable public @org.jetbrains.annotations.Nullable int[] next()
      Creates the next permutation in the sequence.
      Returns:
      An array containing the permutation. The returned array is modified each time this function is called.