# Highlighting edges of a graph

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Hari on 7 Oct 2020
Answered: Steven Lord on 7 Oct 2020
How do I highlight specific edges of a graph? Let's say for the figure given below, I need to highlight the edges 9-16 and 8-15. Please help.

Luciano Garim on 7 Oct 2020
Hi Hari!
I had the same problem. I found the solution here:
https://www.mathworks.com/help/matlab/ref/matlab.graphics.chart.primitive.graphplot.highlight.html
Try these examples above. If you have any difficulty let me know.
I hope helped you!
Hari on 7 Oct 2020
Hi, I have read the documentation. Couldnt figure out how should I give the edges to be highlighted as input.

Ameer Hamza on 7 Oct 2020
Edited: Ameer Hamza on 7 Oct 2020
You can give them a different color and sizes. Here is a simple example
n = 20;
G = graph(1:n, [2:n 1]);
plot(G)
nodes = [5 7 9 11]; % nodes to highlight
colors = [0 0 0; % color for normal nodes
1 0 0]; % color for highlighted nodes
ax = axes();
colormap(colors);
gp = plot(G);
gp.NodeCData = zeros(1, n);
gp.NodeCData(nodes) = 1;
gp.MarkerSize = gp.MarkerSize*ones(1, n);
gp.MarkerSize(nodes) = 10;
Hari on 7 Oct 2020
How did you refer to the edges in this case by giving [1 6 9 14]? Does it select the link having these nodes?
Sorry if this queston is stupid. I'm just a novice programmer.
Ameer Hamza on 7 Oct 2020
No, MATLAB's graph() uses its own internal numbering for edges. If you want to specify edges using the nodes, then try the following code. It specifies nodes at two ends of the edge you want to highlight.
n = 20;
G = graph(1:n, [2:n 1]);
m = size(G.Edges, 1);
nodes = [5 7 9 11]; % nodes to highlight
edges_source = [1; 4; 7; 10];
edges_destination = [2; 5; 8; 11]; % an edge must exist between corresponding nodes of two vectors
edges = G.findedge(edges_source, edges_destination);
colors = [0 0 0; % color for normal nodes
1 0 0]; % color for highlighted nodes
ax = axes();
colormap(colors);
gp = plot(G);
gp.NodeCData = zeros(1, n);
gp.NodeCData(nodes) = 1;
gp.MarkerSize = gp.MarkerSize*ones(1, n);
gp.MarkerSize(nodes) = 10;
gp.EdgeCData = zeros(1, m);
gp.EdgeCData(edges) = 1;
gp.LineWidth = 1*ones(1, m);
gp.LineWidth(edges) = 3;

Steven Lord on 7 Oct 2020
The easiest way for this example is to specify the source and target nodes. Let's plot the bucky graph:
G = graph(bucky);
h = plot(G);
To highlight edge (9, 10) and (29, 43) in red, we specify the source nodes [9 29] and the corresponding target nodes [10 43] as the second and third inputs to highlight. We then tell highlight we want to change the EdgeColor property of those edges to red.
highlight(h, [9 29], [10 43], 'EdgeColor', 'r')