On Nov 6, 2004, at 8:57 AM, Vladimir Prus wrote:
after trying to use the bellman_ford_shortest_paths I think it's a little bit strange. First of all, user is required to initialise distance map before calling the algorithm. The distance to the source vertex must be set to zero and distances to other vertices to infinity. Why can't the algorithm accept a source vertex as parameter and do initialisation itself? Dijsktra surely does not require such initialization.
I believe the intent was to make the Bellman-Ford algorithm require only an Edge List Graph and not also a Vertex List Graph. To set the distance map, one would need the vertices(g) function. However, I agree that it's a bit messy to use, especially when you already have a Vertex List Graph.
Another problem is that number of vertices is passed as parameter. I realize this is more flexible (for example I can compute the maximum length of all paths with less than N edges), but it's also confusing and dangerous. I've just passed a wrong variable to that parameter and spend quite some time debugging.
Same reason: getting n requires num_vertices(g), part of the Vertex List Graph concept.
Is it possible to provide a version of the algorithm which (1) takes just graph, without vertex number parameter (2) takes start vertex, and initialises distance map itself
I expect it would look like this: template <class VertexAndEdgeListGraph, class P, class T, class R> bool bellman_ford_shortest_paths( VertexAndEdgeListGraph& g, typename graph_traits<VertexAndEdgeListGraph>::vertex_descriptor source, const bgl_named_params<P, T, R>& params = all defaults); I'm slightly concerned that adding this overload will cause an ambiguity with the existing bellman_ford_shortest_paths when we have an adjacency list with VertexListS=vecS, but maybe we can weasel around that... One alternative would be to have: template <class VertexAndEdgeListGraph, class P, class T, class R> bool bellman_ford_shortest_paths( VertexAndEdgeListGraph& g, const bgl_named_params<P, T, R>& params = all defaults); Where the mandatory named parameter start_vertex(u) indicates that we should initialize the property maps appropriately for starting at vertex u, and requires a VertexAndEdgeListGraph. This is the safe answer, at least. Doug