How to highlight single edges in an undirected graph?

I am plotting an undirected graph where there exist multiple edges between the same nodes. Now I want to highlight a few of the edges. But only a single edge needs to be highlighted (anyone among the multiple edges between the same node). How do I do that?

I am attaching one graph. You can see both the edges get highlighted in red if two edges exist connecting the same nodes. Instead, I want to highlight only one edge (anyone) and keep the rest of the edges unhighlighted. How to do it for an undirected graph?

Thanks.

Answer 1

[Christine Tobler]

Do you still want the multiple edges to be displayed? If not, you can use the simplify command to reduce all multiple edges to just one.

Otherwise, here is one way to do this:

g = graph([1 1 2 2 3 3], [2 2 3 3 1 1], 'omitselfloops');
p = plot(g);
highlight(p, 1, 2)

figure;
e = findedge(g, 1, 2)

e = 2×1

1 2

p = plot(g);
highlight(p, 'Edges', e(1))

[laha_M]

Thank you. I got your answer for this simple case by applying 'findedge' and mentioning individual node ids. But my edge list is quite extensive and read from a file. I am trying the following. In the actual case, 's' and 't' will be read from the file.

g = graph([1 1 2 2 3 3], [2 2 3 3 1 1], 'omitselfloops');
p = plot(g);
highlight(p, 1, 2);

s = [1 3];
t = [2 1];
figure;
e = findedge(g, s, t);

p = plot(g);
highlight(p, 'Edges', e);

Here both the edges of '1 to 2' and '1 to 3' are highlighted. I only want single edges to be highlighted, keeping the others not highlighted (but present) in the graph. Say one edge from 1 to 2 and another from 1 to 3. How can I do it?

Thanks.

[Christine Tobler]

In that case, you'll need to use the second output of findedge, which in the case of multiple edges tells us which node pair each edge id is coming from:

g = graph([1 1 2 2 3 3], [2 2 3 3 1 1], 'omitselfloops');
p = plot(g);
highlight(p, 1, 2);

s = [1 3];
t = [2 1];
figure;
[e, stID] = findedge(g, s, t)

e = 4×1

1 2 3 4

stID = 4×1

1 1 2 2

[~,uniqueSTid] = unique(stID)

uniqueSTid = 2×1

1 3

p = plot(g);
highlight(p, 'Edges', e(uniqueSTid));

[laha_M]

Thanks.