# How can I know a specific edge from a Graph? Classic List Threaded 2 messages Administrator Am 22.07.20 um 00:12 schrieb spolo96: > Hello everyone, I'm having a hard time dealing with multiple edges in a graph > with the use of gt.shortest_path with negative weights. This is a simple > code that creates a simple graph in order to show my problem: > > g70 = gt.Graph() > > edge_weight = g70.new_edge_property("double") > g70.edge_properties["weight"] = edge_weight > > edges = [[0,1],[1,2],[0,2],[0,2]] > weights = [-1,0,-2, 0] > > for i in range(len(edges)): >     e = g70.add_edge(edges[i], edges[i]) >     g70.ep.weight[e] = weights[i] > > for path in gt.shortest_path(g70, 0, 2, weights=g70.ep.weight, > negative_weights=True): >     print(path) >     > gt.graph_draw(g70, vertex_text=g70.vertex_index, edge_text=g70.ep.weight) > > As you can see in the image, there are 2 edges from node 0 to node 2, the > solution that appears before the image specifies: '0' and target '2' at 0x7f2b70d49930> meaning that the shortest path from > node 0 to node 2 is an edge from node 0 to node 2. However it doesn't > specify which one of the two edges: (0,2) ->0, (0,2)->-2 is the solution > edge. Of course it does. The function returns both the vertices and the edges. The edge descriptors map to a specific edges, which have their own index and properties (such as weight). Just do the following: for e in gt.shortest_path(g70, 0, 2, weights=g70.ep.weight,                           negative_weights=True):     print(e, g70.edge_index[e], g70.ep.weight[e]) which will print: (0, 2) 2 -2.0 Note that it's always obvious which of the parallel edges get selected: it's always the one with the smallest weight, otherwise it would not be part of the shortest path. Best, Tiago -- Tiago de Paula Peixoto <[hidden email]> _______________________________________________ graph-tool mailing list [hidden email] https://lists.skewed.de/mailman/listinfo/graph-tool signature.asc (849 bytes) Download Attachment -- Tiago de Paula Peixoto