From what I understand of Dijkstras search, Dijkstras visitor is invoked at traversal of a vertex. However, this is still separate from the weights which is a required argument the algorithm takes. In my case however, the weight of traversing the edge is a function of cost of traversing to the edge from the origin vertex.

I just used cost * weight as an example. In the actual algorithm, weight(edge) = interval_search(cost(edge[origin_vertex] ), interval_map)

On Sep 18, 2014 7:01 PM, "Tiago Peixoto [via Main discussion list for the graph-tool project]" <[hidden email]> wrote:

On 18.09.2014 11:42, ambasta wrote:

> Hi,
>
> I have two problems
>
> class Weights:
> ...
>
>
> g = Graph(directed=True)
> weights = g.new_edge_property('object')
>
> vertex_one = g.add_vertex()
> vertex_two = g.add_vertex()
> edge = g.add_edge(vertex_one, vertex_two)
> weights[edge] = Weights(1)
>
> g.shortest_path(vertex_one, vertex_two, weights)
>
> This raises ValueError: property map 'dist_map' is not of scalar type. Is
> there a function I can implement in Weights for it to return a scalar value
> to be used during calculation of shortest path.
Take a look at the search module:

https://graph-tool.skewed.de/static/doc/search_module.html

You should use the dijkstra_search() function, and specialize the
DijkstraVisitor class to do what you want.

> Secondly, consider a directed graph where the edge weight is a function of
> cost at edge's origin vertex, i.e. the weight class is defined as:
>
> class Weights:
> ....
> def get_weight(current_cost):
> return self.cost * current_cost
>
>
> Hence during calculation of shortest_path/distance, is it possible to pass
> the weight at the traversed/visited edge to get the cost of the edge.
You can do that with the dijkstra_search() function, as I mentioned
above. However, note that multiplying weights is the same as summing
their logarithms... Hence you could simply use the log of the weights
instead, and save you some trouble.

Best,
Tiago

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