Check visible edge.
Check if the directed edge from x to z in a MAG or in a PAG is visible or not.
visibleEdge(amat, x, z)
amat |
Adjacency matrix of type amat.pag |
x,z |
(integer) position of variable x and z, respectively, in the adjacency matrix. |
All directed edges in DAGs and CPDAGs are said to be visible. Given a MAG M / PAG P, a directed edge A -> B in M / P is visible if there is a vertex C not adjacent to B, such that there is an edge between C and A that is into A, or there is a collider path between C and A that is into A and every non-endpoint vertex on the path is a parent of B. Otherwise A -> B is said to be invisible. (see Maathuis and Colombo (2015), Def. 3.1)
TRUE if edge is visible, otherwise FALSE.
Diego Colombo
M.H. Maathuis and D. Colombo (2015). A generalized backdoor criterion. Annals of Statistics 43 1060-1088.
amat <- matrix(c(0,3,0,0, 2,0,2,3, 0,2,0,3, 0,2,2,0), 4,4)
colnames(amat) <- rownames(amat) <- letters[1:4]
if(require(Rgraphviz)) {
plotAG(amat)
}
visibleEdge(amat, 3, 4) ## visible
visibleEdge(amat, 2, 4) ## visible
visibleEdge(amat, 1, 2) ## invisiblePlease choose more modern alternatives, such as Google Chrome or Mozilla Firefox.