In linear algebra, a permutation matrix is a matrix that has exactly one 1 in each row or column and 0s elsewhere. Permutation matrices are the matrix representation of permutations.
For example, the permutation matrix corresponding to σ=(1)(2 4 5 3) is
- PσPπ=Pσπ for any two permutations σ and π on n objects.
- P(1) is the identity matrix.
- Permutation matrices are orthogonal matrices and (Pσ)-1=P(σ-1).
A permutation matrix is a stochastic matrix; in fact doubly stochastic. One can show that all doubly stochastic matrices of a fixed size are convex linear combinations of permutation matrices, giving them a characterisation as the set of extreme points.