Memory leak (igraph, watts.strogatz.game, get.all.shortest.paths)

Memory leak (igraph, watts.strogatz.game, get.all.shortest.paths)

I try to make a quite simple computation but I get an out of memory
message whose origin is not clear to me. Here is what I want: for the
small-world model (watts.strogatz.game) and several p-values I create
nsamp many graphs and compute the distance between the first node and the
opposite node at n/2. When nsamp = 1, everything works fine. Setting it to
100 or larger gives an "out of memory" error right in the first round
(i=1, j=5), i.e., for the smallest p-value (0.01). Setting nsamp=10 gives
no error (huh?? Shouldn't that include i=1, j=5?). I tried to explicitly
remove all the larger objects (graph, len) but to no avail. Any ideas
here? Here is the code:
require(igraph)
probs <- c(1:25)*0.01
n = 1000
target <- n/2
nsamp = 100
for(i in c(1:length(probs))){
for(j in c(1:nsamp)){
graph <- watts.strogatz.game(dim=1, size=n, p=probs[i], nei=4)
shortest.paths(graph, v=V(graph)[1], to=V(graph)[target])
len <- get.all.shortest.paths(graph, from=V(graph)[1])
rm(graph)
#The number of shortest paths between 1 and target can be found in
numbPathsBetw1AndTarget <- len$nrgeo[target]
#In len$res there are all shortest paths between node 1 and all other
#nodes. It comes as a list which at each point contains a vector of
#so we need to use lapply to find out which of
#the lists are of interest to us.
lengths <- unlist(lapply(len$res, function(x) length(x)))
rm(len)
}
}
I am aware that I can increase the memory, but it bugs me that for nsamp
being small everything is fine. It seems to be a memory leak but I do not
there where it comes into play.
Edit: it is so unreproducible that I suspect it is not a memory leak but
rather a bad configuration of the graph. It always happens for i=1 but for
different j. Thus: is there an intrinsic, upper limit on the diameter of
the graph to apply get.all.shortest.paths or on the number of shortest
paths?