Re: [jgrapht-users] add edge to directed graph in both directions

[Dimitris M. <dma...@cs...>]

Hi Joris,

I remember that in the last entry on the referred thread 
(http://jgrapht-users.107614.n3.nabble.com/Mixed-graphs-td4024952.html), 
krutor said something about creating his/her own implementation to solve 
this exact problem. It would be awesome if krutor could share the code 
with everyone by contributing to the project's github repository!

Best,
Dimitris


On 23/06/2015 08:27 μμ, Joris Kinable wrote:
> Hm, I remember seeing that thread. The two solutions proposed were:
>
> 1. Create 2 graphs, a directed and an undirected graph, and create a 
> GraphUnion from these two graphs. This approach has 2 major disadvantages:
> -The GraphUnion is read-only, so removing a vertex or edge (which are 
> both well defined operations in 'mixed' graphs) are not supported
> -Several algorithms in JgraphT won't work well. For example, one may 
> be interested in finding all Strongly Connected Components in the 
> graph (which again is well-defined for mixed graphs). 
> The StrongConnectivityInspector class for example in JgraphT expects a 
> DirectedGraph as input, and hence, will not accept the GraphUnion.
>
> 2. To represent an undirected edge e=(i,j) in a directed graph, create 
> 2 edge objects, say e1 and e2, which contain the same information, and 
> add them to the directed graph:
> directedGraph.addEdge(i,j,e1);
> directedGraph.addEdge(j,i,e2);
> This approach has again 2 major disadvantages:
> -e1 and e2 duplicate the same information, thereby causing a lot of 
> memory overhead
> -It may prove very difficult to keep the information in the objects e1 
> and e2 synchronized.
>
> So far, neither of these approaches seem desirable. Any remarks on this?
>
> Joris
>
>
> On Tue, Jun 23, 2015 at 12:52 PM, Szabolcs Besenyei 
> <bes...@gm... <mailto:bes...@gm...>> wrote:
>
>     http://jgrapht-users.107614.n3.nabble.com/Mixed-graphs-td4024952.html
>
>     Üdvözlettel,
>
>     Besenyei Szabolcs
>
>     2015-06-23 18:30 GMT+02:00 Joris Kinable <de...@gm...
>     <mailto:de...@gm...>>:
>
>         Say I have a list of directed and undirected edges which I
>         would like to represent in the same graph. Every undirected
>         edge (i,j) can be represented in a directed graph by adding
>         two arcs: (i,j) and (j,i). The following code does however
>         *not* achieve this:
>
>         public  static void main(String[] args){
>             DirectedGraph<Integer, String> directedGraph=new
>         SimpleDirectedGraph<Integer, String>(String.class);
>             String s="UndirectedEdge";
>             directedGraph.addVertex(1);
>             directedGraph.addVertex(2);
>         System.out.println(directedGraph.addEdge(1,2,s));
>         System.out.println(directedGraph.addEdge(2,1,s));
>         }
>
>         The second addEdge call will return false because edge s is
>         already in the graph. What would be a clean way to resolve
>         this issue?
>
>         Thanks,
>
>         Joris
>
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