Permutation

In mathematics, the notion of permutation relates to the act of arranging all the members of a set into some sequence or order, or if the set is already ordered, rearranging (reordering) its elements, a process called permuting.

Examples

For example, written as tuples, there are six permutations of the set {1,2,3}, namely:

• (1,2,3)
• (1,3,2)
• (2,1,3)
• (2,3,1)
• (3,1,2)
• (3,2,1)

These are all the possible orderings of this three element set.

As another example, an anagram of a word, all of whose letters are different, is a permutation of its letters. In this example, the letters are already ordered in the original word and the anagram is a reordering of the letters.

Combinatorics

The study of permutations of finite sets is a topic in the field of combinatorics.

Areas of mathematics

Permutations occur, in more or less prominent ways, in almost every area of mathematics.

They often arise when different orderings on certain finite sets are considered, possibly only because one wants to ignore such orderings and needs to know how many configurations are thus identified.

For similar reasons permutations arise in the study of sorting algorithms in computer science.

The number of permutations of n distinct objects is n factorial usually written as n!, which means the product of all positive integers less than or equal to n.

Algebra and group theory

In algebra and particularly in group theory, a permutation of a set S is defined as a bijection from S to itself.

That is, it is a function from S to S for which every element occurs exactly once as an image value.

This is related to the rearrangement of the elements of S in which each element s is replaced by the corresponding f(s).

The collection of such permutations form a group called the symmetric group of S.

The key to this group's structure is the fact that the composition of two permutations (performing two given rearrangements in succession) results in another rearrangement.

Permutations may act on structured objects by:

• Rearranging their components
• Replacement (substitution) of symbols

Combinations

Combinations are selections of some members of a set where order is disregarded.

Elementary combinatorics

In elementary combinatorics, the k-permutations, or partial permutations, are the ordered arrangements of k distinct elements selected from a set. When k is equal to the size of the set, these are the permutations of the set.

See also

• Alternating permutation
• Binomial coefficient
• Combination
• Combinatorics
• Convolution
• Cyclic order
• Cyclic permutation
• Element (mathematics)
• Even and odd permutations
• Factorial number system
• Josephus permutation
• Levi-Civita symbol
• List of permutation topics
• Major index
• Mathematics
• Necklace (combinatorics)
• Permutation group
• Permutation pattern
• Permutation polynomial
• Permutation representation (symmetric group)
• Probability
• Random permutation
• Rencontres numbers
• Sorting network
• Substitution
• Substitution cipher
• Superpattern
• Symbol
• Symmetric group
• Tuple
• Twelvefold way
• Weak order of permutations

External links

• Permutation @ Wikipedia