Re: [Boost-users] Directed cycle detection in a DAG between two nodes

2013/2/20 John Lilley

Check out Floyd’s algorithm (http://en.wikipedia.org/wiki/Cycle_detection) for a clever approach. ****

Basically you walk this algorithm starting with each node in turn. ****

It requires no extra storage, but it will be faster if you track already-visited nodes and skip them later.****

If you can make your algorithm intrusive, adding a “bool visited” member to your nodes removes the need for an external set.****

john****

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*From:* Boost-users [mailto:boost-users-bounces@lists.boost.org] *On Behalf Of *Michael Powell *Sent:* Wednesday, February 20, 2013 5:41 AM *To:* boost-users@lists.boost.org *Subject:* Re: [Boost-users] Directed cycle detection in a DAG between two nodes****

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I can't speak to how your graph is wired up, but it seems to me that somehow you need to keep track of nodes visited, more than simply nodeInit (possibly).

I didn't do this in C++ boost, per se, but I have done something similar in C# .NET using PowerCollections Graph. I had different node traversals analyzing volumetric flow (pipes, substance, etc) through different connectors (valves, and such), and needed to analyze communication between volumes.

Enter graph traversal. I ended up keeping track of nodes visited to detect my terminal case. Very fast, very clean, if a little inefficient because of the overhead needing a collection (list, C++ STL vector if you will). You pass in a new vector<> and could be the same one throughout the recursive call.

Worked like a charm.

Good hunting!

Regards,

Michael****

On Wed, Feb 20, 2013 at 4:20 AM, Amanullah Yasin wrote:****

Hi,****

In Hill Climbing algorithm, before applying an operation "add_edge", "reverse_edge" or "remove_edge", I need to check whether the graph will be a Directed Acyclic Graph (DAG) or not. So there is recursive function but in some cases it goes in infinite loop and gives "stack overflow" error.** **

//======= Function ======= bool myAlgo::remainsADAG(const Node_type& nodeInit, const Node_type& node, const Graph_type& graph)****

{ graph_traits::adjacency_iterator vi, vi_end; tie(vi, vi_end) = adjacent_vertices(node, graph);

for (; vi != vi_end; ++vi) { if ((*vi == nodeInit) || (!remainsADAG(nodeInit, *vi, graph))) return false; } return true; } ==============****

e.g. for Graph ****

12->19->20->23 19->24->31->18>19 18->32

To test if there is a directed path between v12 and v32****

it goes as:****

12->19->20->23 ****

24->31->18>19****

*There is an infinite loop{18->19->20->23, 24->31->18}.* =================****

Can some one help me or is there any other easy way to find a directed path between two nodes in boost graph?****

Thanks in advance.****

YASIN****

Why not just use the boost topological_sort function on your graph. It will fail if there is a cycle. In that case, catch the exception and then use the boost depth_first_search function to identify the cycle. I can send you a code sample if it helps.

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