# code by Christopher G. Watson; [email protected]

local.eff <- function(g) {
  if ('degree' %in% vertex_attr_names(g)) {
    degs <- V(g)$degree
  } else {
    degs <- degree(g)
  }

  eff <- numeric(length(degs))
  nodes <- which(degs > 1)

  eff[nodes] <- simplify2array(mclapply(nodes, function(x) {
    neighbs <- neighbors(g, v=x)
    g.sub <- induced.subgraph(g, neighbs)
    Nv <- vcount(g.sub)

    paths <- shortest.paths(g.sub, weights=NA)
    paths <- paths[upper.tri(paths)]
    2 / Nv / (Nv - 1) * sum(1 / paths[paths != 0])
    }, mc.cores=detectCores())
  )
eff
}