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permutations (version 1.1-6)

stabilizer: Stabilizer of a permutation

Description

A permutation ϕ is said to stabilize a set S if the image of S under ϕ is a subset of S, that is, if {ϕ(s)|sS}S. This may be written ϕ(S)S. Given a vector G of permutations, we define the stabilizer of S in G to be those elements of G that stabilize S.

Given S, it is clear that the identity permutation stabilizes S, and if ϕ,ψ stabilize S then so does ϕψ, and so does ϕ1 [ϕ is a bijection from S to itself].

Usage

stabilizes(a,s)
stabilizer(a,s)

Value

A boolean vector [stabilizes()] or a vector of permutations in cycle form [stabilizer()]

Arguments

a

Permutation (coerced to class cycle)

s

Subset of {1,,n}, to be stabilized

Author

Robin K. S. Hankin

Examples

Run this code

a <- rperm(200)
stabilizer(a,3:4)

all_perms_shape(c(1,1,2,2)) |> stabilizer(2:3)  # some include (23), some don't


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