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How to find all related nodes in directed graph?

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Artur Iskhakov
Artur Iskhakov on 3 Jul 2020
Commented: Christine Tobler on 10 Jul 2020
Hi! I have a dirested graph "G" (figure is represented bellow). How can I find all nodes that are ONE BY ONE connected with certain node "n". For example if we talk about node 11 required nodes are 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23.
I tried to use a "successors" function but I'm stcuk. Can anybody help me please? Here's the code (my attempts):
clc; clear;
S = [1 2 3 3 4 5 6 6 8 9 11 11 12 12 14 16 16 17 17 19 20 22];
T = [2 3 4 11 5 6 7 8 9 10 12 16 13 14 15 17 22 18 19 20 21 23];
weight = [0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0];
G = digraph (S, T, weight);
B = [S' T' weight'];
for i = 1:22
if B(i,3)==1
N = successors (G, B(i,2)) %% equivalent of N = (12; 16)
k = N';
for j=1:length(N)
N = successors(G,N(j))
end
end
end

Answers (2)

Steven Lord
Steven Lord on 3 Jul 2020
You want to know all nodes that are reachable from the designated node? Use the distances function on the digraph with the designated node as the source node.

Christine Tobler
Christine Tobler on 6 Jul 2020
Edited: Christine Tobler on 6 Jul 2020
Another option is to use the weak connected components of the graph:
bins = conncomp(G, 'Type', 'weak');
% bins(nid) gives the id of the connected component that contains node nid.
allNodesInSameComponentAsNode11 = find(bins == bins(11))
  2 Comments
Christine Tobler
Christine Tobler on 10 Jul 2020
Sorry I just came back to this now. On second look, I realize I misinterpreted your question (I thought you were looking for all nodes connected to node 11 when ignoring edge direction).
If you are looking for reachable nodes only, you can use
nearest(G, 11, Inf, 'Method', 'unweighted')
which will return all nodes within distance Inf of node 11, meaning all nodes that are reachable from node 11.
It's also possible to use distances, as Steve suggested, just find all nodes where the distance to node 11 is not Inf.

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