After some examination, igraph's calculations for density of a graph with self-loops is counter to what I expected. Here is what I expected (in R) assuming an undirected, unweighted graph G with adjacency matrix 'A' (of R class 'matrix'):
( sum(A[upper.tri(A)]) + sum(diag(A)) )/((n*(n-1)/2) + n) However, igraph's graph.density(G,loops=T) calculates: ( sum(A[upper.tri(A)]) + sum(diag(A)) )/((n*(n-1)/2) + n/2) Would someone point me to some literature that states the self-loop part of the divisor in an undirected graph should be halved? Or is igraph's calculation incorrect? Thanks. Jay
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