DG function

Directed graphs

Defines the adjacency of a directed graph.

DG(...)

Arguments

• ...: a sequence of model formulae

Details

The directed graph is defined by a sequence of models formulae. For each formula the response defines a node of the graph and its parents. The graph contains no loops.

Returns

the adjacency matrix of the directed graph, i.e., a square Boolean matrix of order equal to the number of nodes of the graph and a one in position $(i,j)$ if there is an arrow from $i$ to $j$ and zero otherwise. The dimnames of the adjacency matrix are the labels for the nodes of the graph.

References

Lauritzen, S. (1996). Graphical models. Oxford: Clarendon Press.

Author(s)

G. M. Marchetti

See Also

DAG, UG

Examples

## A DAG
DG(y ~ x, x ~ z, z ~ u)

## A cyclic directed graph
DG(y ~ x, x ~ z, z ~ y)

## A graph with two arrows between two nodes
DG(y ~ x, x ~ y)

## There can be isolated nodes
DG(y ~ x, x ~ x)