id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	revision
623	Different ids assigned to the same edge in an undirected graph	Francesco Carrabs	Alpar Juttner	"Dear LEMON developers,
I would like to report a problem regarding multiple ids associated with the same edge in an undirected graph.
Let us consider the following code in which I define a complete undirected graph with 3 nodes:

{{{
#include <iostream>
#include <lemon/list_graph.h>

using lemon::INVALID;
using namespace std;

int main() {

    lemon::ListGraph g;
    for(int i=0;i<3;i++){
        g.addNode();
    }
    for(int i=0;i<3;i++){
        for(int j=0;j<3;j++){
            if(i<j)
                g.addEdge(g.nodeFromId(i),g.nodeFromId(j));
        }
    }

    cout<<""Edge of the graph: ""<<endl;
    for(lemon::ListGraph::EdgeIt e(g); e!=INVALID;++e){
        cout<<""Edge {""<<g.id(g.u(e))<<"",""<<g.id(g.v(e))<<""}: id= ""<<g.id(e) << endl;
    }

    cout<<""IncEdge of the graph: ""<<endl;
    for(lemon::ListGraph::NodeIt i(g); i!=INVALID; ++i){
        for(lemon::ListGraph::IncEdgeIt e(g, i); e != INVALID; ++e)
            cout<<""Edge {""<<g.id(g.baseNode(e))<<"",""<<g.id(g.runningNode(e))<<""}: id= ""<<g.id(e)<<endl;
    }
}
}}}

Notice that I ask to print the id in two different ways: by iterating on all the edges of the graph and by iterating on the nodes of the graph and, for each node, by considering its incident edges. The output of the previous code is:

Edge of the graph:
Edge {1,2}: id= 2
Edge {0,2}: id= 1
Edge {0,1}: id= 0

IncEdge of the graph:
Edge {2,1}: id= 4
Edge {2,0}: id= 2
Edge {1,2}: id= 5
Edge {1,0}: id= 0
Edge {0,2}: id= 3
Edge {0,1}: id= 1

You can notice that to the edge {0,1} are assigned the id 0 (loop on the edges) and 1 (loop on the incident edges)."	defect	closed	major	LEMON 1.4 release	core	hg main	fixed