Use this if you are using igraph from R
This function tests whether the given graph is a DAG, a directed acyclic graph.
The input graph. It may be undirected, in which case
is_dag checks whether there is a directed cycle in the graph. If not,
the graph is a DAG.
A logical vector of length one.
g <- make_tree(10) is_dag(g) g2 <- g + edge(5,1) is_dag(g2)