MATLAB: Is it possible to set an alpha value for each edge in a GraphPlot

graphgraph theoryMATLABplotting

Colours for individual edges can be set.

% For individual edges
highlight(H, edge_idx, 'EdgeColour', [1,0,0]);
% For all edges
H.EdgeColour = % matrix with RGB-values for each edge

Opacity for all edges in the graph can be set, too.

H.EdgeAlpha = 0.01;

Unfortunately I cannot find a way to set alpha values for individual edges. Ideally, there should be a fourth channel in H.EdgeColour to control opacity.

Has anyone found a workaround?

Best Answer

Hi Michael,

We do not provide a way to set EdgeAlpha to be different for each edge. We just didn't expect this to be very useful, thinking it would be hard to read these subtle differences in a graph.

For the special case where you want all edges to either have the same alpha or be completely transparent, you could instead use 'LineStyle', 'none' to make some edges completely invisible (use the highlight method for a simpler way to do this).

If you are looking for something else, could you tell me more about what you are doing? What do the different alpha's represent? Are there only a few different alpha values, or is each one slightly different?

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I'm afraid it's not possible to have both directed and undirected edges in the same graph. To convert a graph to a digraph, you could use

 gDirected = digraph(adjacency(gUndirected));

This will replace every undirected edge with two directed edges going in opposing directions. You could then use rmedge to remove the edges that go in the direction you don't want.

Within most graph algorithms, these two edges will behave the same way as the undirected edge did - but of course, the plot will look very different.

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One easy way to do this is to highlight the edges you want to change.

g = graph(bucky);
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Note that you don't need to change one node and/or edge at a time; you can specify a path if you want.

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  'LineWidth', 2, ...           % that are wider than the others
  'MarkerSize', 8, ...          % and have larger
  'NodeColor', 'c', ...         % cyan
  'Marker', 's', );             % squares as the markers

Best Answer

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