mathematics 1. 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 you can find an inverse permutation
that reverses the action of any given permutation.
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
What the football pools call a "permutation" is not a
permutation but a
combination - the order does not matter.
same set and so
f(f'(x)) = f'(f(x)) = x.
(2001-05-10)