find.unsh.triple {pcalg}

Find all Unshielded Triples in an Undirected Graph

Description

Find all unshielded triples in an undirected graph, q, i.e., the ordered ((x,y,z) with x < z) list of all the triples in the graph.

Usage

find.unsh.triple(g, check=TRUE)

Arguments

g

adjacency matrix of type amat.cpdag representing the skeleton; since a skeleton consists only of undirected edges, g must be symmetric.

check

logical indicating that the symmetry of g should be checked.

Details

A triple of nodes x, y and z is “unshielded”, if (all of these are true):

(i)

x and y are connected;

(ii)

y and z are connected;

(iii)

x and z are not connected.

Value

unshTripl

Matrix with 3 rows containing in each column an unshielded triple

unshVect

Vector containing the unique number for each column in unshTripl (for internal use only)

Author(s)

Diego Colombo, Markus Kalisch ([e-mail]), and Martin Maechler

Examples

data(gmG)
if (require(Rgraphviz)) {
  ## show graph
  plot(gmG$g, main = "True DAG")
}

## prepare skeleton use in example
g <- wgtMatrix(gmG$g) ## compute weight matrix
g <- 1*(g != 0) # wgts --> 0/1; still lower triangular
print.table(g, zero.print=".")
skel <- g + t(g) ## adjacency matrix of skeleton

## estimate unshielded triples -- there are  13 :
(uTr <- find.unsh.triple(skel))