hrg creates a HRG from an igraph graph. The igraph graph must be
a directed binary tree, with \(n-1\) internal and \(n\) leaf
vertices. The prob argument contains the HRG probability labels
for each vertex; these are ignored for leaf vertices.
hrg(graph, prob)The igraph graph to create the HRG from.
A vector of probabilities, one for each vertex, in the order of vertex ids.
hrg returns an igraphHRG object.
Other hierarchical random graph functions: consensus_tree,
  fit_hrg, hrg-methods,
  hrg_tree, predict_edges,
  print.igraphHRGConsensus,
  print.igraphHRG, sample_hrg