For a directed graph the underlying graph is the graph that is
constructed where all edge orientation is ignored. This function
carries out such a transformation on
graph is already undirected then it is simply
graph is a multi-graph (has multiple edges) an error is
thrown as it is unclear how to compute the underlying graph in that
The method will work for any
graph subclass for which an
edgeMatrix method exists.
An instance of
graphNELwith the same nodes as the input but which is
Graph Theory and its Applications, J. Gross and J. Yellen.
V <- letters[1:4] edL2 <- vector("list", length=4) names(edL2) <- V for(i in 1:4) edL2[[i]] <- list(edges=c(2,1,2,1)[i], weights=sqrt(i)) gR2 <- graphNEL(nodes=V, edgeL=edL2, edgemode="directed") ugraph(gR2)