R: Edge matrix of a graph

edgematrix {ggm} | R Documentation

## Edge matrix of a graph

### Description

Transforms the adjacency matrix of a graph into an “edge matrix”.

### Usage

    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.

### Value

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

### Author(s)

Giovanni M. Marchetti

### 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.

### See Also

`adjMatrix`

### Examples

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

[Package ggm version 2.3 Index]