
From:  PierreAndre Maugis 
Subject:  Re: [igraph] NonBacktracking Matrix 
Date:  Thu, 30 Jan 2014 09:56:04 +0000 
get.backtrack < function(g){
n < ecount(g)
g < as.directed(g)
h < line.graph(g)
P < rbind(1:n,(n+1):(2*n))
P < cbind(P,P[c(2,1),])
h < h  edges(E(h,P))
get.adjacency(h)
}
Hello,I am trying to build the nonbacktracking matrix of a network. It is the matrix whose entries are indexed by the edges of the graph. Entries are 0 if the said edges do not form a path of length two, and 1 if they do. More details can be found in arXiv:1306.5550, p3.All the algorithms I could produce are very slow. Computing the entries is not a problem, however storing them properly in the matrix is, and takes a lot of time.I would welcome any suggestion on the topic.Best,PierreAndré Maugis
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