edgematrix function

Edge matrix of a graph

Transforms the adjacency matrix of a graph into an ``edge matrix''.

edgematrix(E, inv=FALSE)

Arguments

• E: a square matrix, representing the adjacency matrix of a graph.
• inv: a logical value.

Details

In some matrix computations for graph objects the adjacency matrix of the graph is transformed into an ``edge matrix''. Briefly, if $E$ is the adjacency matrix of the graph, the edge matrix is $A = sign(E+I)^T=[a_{ij}]$. Thus, $A$ has ones along the diagonal and if the graph has no edge between nodes $i$ and $j$ the entries $a_{i,j}$ and $a_{j,i}$ are both zero. If there is an arrow from $j$ to $i$

$a_{i,j}=1$ and $a_{j,i} = 0$. If there is an undirected edge, both $a_{i,j}=a_{j,i}=1$.

Returns

• A: the edge matrix of the graph. If TRUE the nodes are sorted in inverted topological order and the edge matrix is upper triangular.

References

Wermuth, N. (2003). Analysing social science data with graphical Markov models. In: Highly Structured Stochastic Systems. P. Green, N. Hjort & T. Richardson (eds.), 47--52. Oxford: Oxford University Press.

Author(s)

Giovanni M. Marchetti

See Also

adjMatrix

Examples

amat <- DAG(y ~ x+z, z~u+v)
amat
edgematrix(amat)
edgematrix(amat, inv=TRUE)