pcalg (version 2.4-3)

legal.path: Check if a 3-node-path is Legal

Description

Check if the path $a-b-c$ is legal.

A 3-node path $a-b-c$ is “legal” iff either $b$ is a collider or $a-b-c$ is a triangle.

Usage

legal.path(a, b, c, amat)

Arguments

a,b,c

(integer) positions in adjacency matrix of nodes $a$, $b$, and $c$, respectively.

amat

Adjacency matrix (coding 0,1,2,3 for no edge, circle, arrowhead, tail; e.g., amat[a,b] = 2 and amat[b,a] = 3 implies a -> b)

Value

if path is legal, otherwise FALSE.

Examples

amat <- matrix( c(0,1,1,0,0, 2,0,1,0,0, 2,2,0,2,1,
                  0,0,1,0,0, 0,0,2,0,0), 5,5)
legal.path(1,3,5, amat)
legal.path(1,2,3, amat)
legal.path(2,3,4, amat)