# THE GRAPH FUNCTION DOESN'T CONSIDER WEIGHTS

2 views (last 30 days)
Gianluca Angelini on 30 Jan 2022
Hi to everybody, in my code I am trying to calculate the shortest path from a graph, whose I have explicited all parameters.
But from some checks I have done, it seems like the shortestpath function doesn't consider the weights I have putted in the graph. In fact I have manually specified some extremely high values for some of the edges of my graph so that the shortestpath function should avoid them in its calculation, but it doen't happen. I specify that no negative values are present in the Graph.Edges.Weight array.
Are there some tricks to consider, or some advice you can give me to solve my trouble or to understand why shortestpath function doesn't work properly?

Christine Tobler on 31 Jan 2022
Hard to say what's going wrong without seeing your code. Here's an example where you can see the weights being used to decide on the path:
g = graph([1 2 3], [2 3 1], [1 2 100]);
plot(g, 'EdgeLabel', g.Edges.Weight)
[path, dist] = shortestpath(g, 1, 3)
path = 1×3
1 2 3
dist = 3
[path, dist] = shortestpath(g, 1, 3, 'Method', 'unweighted')
path = 1×2
1 3
dist = 1
Gianluca Angelini on 4 Feb 2022
I will maintain the line with the rmnedge function in my code in order to avoid the edges with high weights.

Steven Lord on 30 Jan 2022
Are you representing your graph as a graph or digraph object or as a biograph object?
How have you stored / represented your weights? If a graph or digraph does your object's edges table G.Edges contain a variable named Weight? [Weights won't do, it must be named exactly Weight.]
What algorithm did you tell shortestpath to use in determining the shortest path? If you're using a biograph did you specify BFS as the method?
Gianluca Angelini on 30 Jan 2022
I confirm I have used the graph object and its weights are stored in a G.Edges.Weight array.
Concerning the shortestpath, I have used this:
shortestpath(G,start_id,finish_id,'Method','positive');

R2018b

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