# Create a graph from removed edges

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Sim on 20 Apr 2020
Edited: Sim on 20 Apr 2020
Hi, I have a graph G, from which I removed some edges, getting Grm.
Now I would need to get the graph composed only by the removed edges, but with the same nodes as in G, i.e. the graph G2 = G - Grm.
The following works:
% create a graph "G" and plot it
s = [1 1 1 2 3 4 4 5 5 6 7];
t = [2 4 8 3 4 5 8 6 8 7 8];
x = [0.5 1 1.5 1.5 1.5 1 0.5 0.5];
y = [0.5 0.5 0.5 1 1.5 1.5 1.5 1];
G = graph(s,t);
G.Nodes.X = x'; G.Nodes.Y = y';
plot(G,'XData',x,'YData',y)
% remove edges and plot the remaining graph "Grm"
rm_s = [1 4 4];
rm_t = [8 5 8];
Grm = rmedge(G,rm_s,rm_t);
figure
plot(Grm,'XData',x,'YData',y)
% plot the graph of removed edges "G2 = G - Grm"
G2 = graph(rm_s,rm_t)
figure
plot(G2,'XData',x,'YData',y)
Unfortunately, this does not work anymore when the edges rm_s and rm_t composing G2 are not composed by the last node in the s and t sets . For example, that does not work by removing the following edges (as you can see I don't remove any edge composed by the node 8, which is the last node in the s and t sets):
rm_s = [1 4];
rm_t = [4 5];
Is there any smart way to create G2 in the very likely case that the "removed edges", which is composed of, do not include the last node in the s and t sets?
Maybe directly from G, by removing all edges, excluding rm_s and rm_t?
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### Accepted Answer

Christine Tobler on 20 Apr 2020
The graph constructor has a syntax that specifies the number of nodes of the graph:
graph(s, t, [], numnodes)
if you pass the number of nodes of G in that should address it.
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Sim on 20 Apr 2020
Thanks a lot! It is working!
For the above mentioned example I used:
G2 = graph(rm_s,rm_t,[],8)

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