perturbation

n 1: an unhappy and worried mental state; "there was too much

anger and disturbance"; "she didn't realize the upset

she caused me" [syn: {disturbance}, {upset}]

2: activity that is an intrusion or interruption; "he looked

around for the source of the disturbance"; "there was a

disturbance of neural function" [syn: {disturbance}]

3: a disposition that is confused or nervous and upset [syn: {fluster}]

4: the act of causing disorder [syn: {disruption}]

permutation

An ordering of a certain number of elements of a

given set.

For instance, the permutations of (1,2,3) are (1,2,3) (2,3,1)

(3,1,2) (3,2,1) (1,3,2) (2,1,3).

Permutations form one of the canonical examples of a "{group}"

- they can be composed and that you can find an inverse

permutation that reverses the action of any given permutation.

A permutation is a {bijection}.

The number of permutations of r things taken from a set of n

is

n P r ◦ n! / (n-r)!

where "n P r" is usually written with n and r as subscripts

and n! is the {factorial} of n.

What the football pools call a "permutation" is not a

permutation but a {combination} - the order does not matter.

(1995-04-10)