This is big, these algorithms are useful for a ton of things (and can get very expensive in big sets)
The Osmand/Organic Maps devs know about this?
It's not that useful for them. This is for calculating the shortest path from a single source to all other vertices in the graph, but for route finding you only need to know a single path.
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This is awesome! I'm reading through their paper right now, and might try to implement it to see how it works in practice.
In case anyone's curious, still working on it. It's not as simple as something like Dijkstra's algorithm.
What's really interesting is the requirement that it seems to place on the graph itself. From what I can tell, the graph it wants to use is a graph where each node has a maximum in-degree of 2 and maximum out-degree of 2, with a total degree of no greater than 3. A traditional di-graph can be converted to this format by splitting each node into a strongly connected cycle of nodes, with each node in the cycle containing the in-edge and out-edge needed to maintain that cycle (with weights of 0) plus one of the previous edges.
Theorerically, this invariant can be held by the graph data structure itself by adding nodes as needed when adding edges. That's what my implementation is doing to avoid having the cost of converting the graph each time you run the algorithm. In this case, one of these node cycles represents your higher level concept of a node (which I'm calling a node group).
The block-based list is also interesting, and I've been having trouble converting it to a data structure in code. I'm still working through the paper though, so hopefully that isn't too bad to get done.
Super interesting; I wonder whether the fraction of nodes that need to be represented by cycles eats into the performance benefit vs. other approaches.
This might be a stupid question but I have just some limited experience with sorting algorithms and was wondering something: could some algorithm like this be improved specifically for multi-threaded processing? I mean, an algorithm that is generally NOT the best option with a single thread, become better than other algorithms when it can delegate part of the work to different threads?
Perhaps something that runs the same algorithm on several threads, each starting at a different point of the map, but sharing their findings with the other threads?
Algorithms can be designed for multithreading yes. Divide and conquer algorithms, like this one, break the problem into independent chunks, and a map reduce on that work can force it to be done across multiple threads.
The real question is whether you gain anything from it. Creating a thread and sending data back and forth has a cost as well, and it's usually a pretty big one relative to the work being done.
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