Re: [igraph] : multiple edges

[patricia]

Hello,

I want to build non-directed and weighted graphs with average degree ranging 1-5 (variation variable g). The weights are assigned to edges are stored in W (symmetric matrix of size 300 x 300, which is not changed) matrix. The stretch of the highlighted code creates multiple edges, for this reason, I am using the igraph_simplify () function. But probably the logic of the code is incorrect, because the weight of the same edge is changing when the average degree undergoes variation. For example, if I have 20 vertex connected to vertex 40 weighing 0123 on a graph with average degree equal to 1, when the average degree is incremented the same edge appears with a distinct weight, for example, 0555. The weights should remain constant throughout the execution of the code, because the matrix W keeps unchanged.     Segue abaixo, o trecho de código.:

void TNetData::MatrixSimilarity(float sigma, int degree_initial, int degree_final)
{
    VectorXf v1, v2;
    MatrixXf W(NOS,NOS);
    int g, i, j, from, to;
    float value, degree_average, similarity;
    igraph_integer_t eid;
    igraph_vector_t  weights, degree;
  

    igraph_attribute_combination_t edge_comb;
    igraph_attribute_combination(&edge_comb, "weight" , IGRAPH_ATTRIBUTE_COMBINE_FIRST, IGRAPH_NO_MORE_ATTRIBUTES);

    igraph_vector_init(&weights, 0);
    igraph_vector_init(&degree,NOS);
    igraph_vector_null(&degree);
    W = ArrayXXf::Zero(NOS,NOS);

    SETGAN(&net,"weighted", 1);

    nSigma = sigma;
    sigma = sigma*sigma*2.0;
 
    //  Construction of symmetric weight matrix

    for (i = 0 ; i < NOS ; i++){
        v1 = data.row(i);
        for (j = 0 ; j < NOS ; j++){
                if(i == j)
                {
                    W(i,j) = 0.0;
                    W(j,i) = 0.0;
                }
                else{
                v2 = data.row(j);
                value = dist.GetDistance(v1,v2);
                value = value / sigma;
                value = exp(-value);
                W(i,j) = value;    // value is obtained using the Euclidean distance between vectors of examples
                W(j,i) = value;
            }
        }
    }

    for(g = initial_degree; g <= final_degree; g++)     // g variation of the average degree
    {

        igraph_degree(&net, &degree, igraph_vss_all(), IGRAPH_ALL, IGRAPH_NO_LOOPS);
        degree_average = (igraph_vector_sum(&degree)/(float)NOS);
        eid = 0;
        while(degree_average <= (float)g)
        {
            do
            {
                from = (rand()%(NOS-1));  //  vertices are drawn and connected // NOS - number of Samples
                to = (rand()%(NOS-1));
            }while(from == to);

            igraph_add_edge(&net,from,to);    // edge is connected to the graph
            similarity = W(from,to) = W(to,from);   // similarity variable receives the value of the weight stored in W
            //igraph_vector_push_back(&weights,similarity);
            SETEAN(&net, "weight", eid, similarity);    //    the edge is set to the value of the weight matrix W sought in
            eid++;   //  stores the number of edges connected to the graph
            igraph_degree(&net, &degree, igraph_vss_all(), IGRAPH_ALL, IGRAPH_NO_LOOPS);
            degree_average = (igraph_vector_sum(&degree)/(float)NOS);    // average degree is calculated
        }

        //for (i = 0; i < eid; i++)
        //{
            //SETEAN(&net, "weight", i, VECTOR(weights)[i]);
        //}

        igraph_simplify(&net,1,1,&edge_comb);

        SaveNetwork(g);   //  method responsible for saving the graph generated for each average degree
    }

    igraph_vector_destroy(&weights);
    igraph_vector_destroy(&degree);
    igraph_attribute_combination_destroy(&edge_comb);
}    

Thank you!

> Date: Tue, 18 Nov 2014 10:44:58 +0100
> From: address@hidden
> To: address@hidden
> Subject: Re: [igraph] : multiple edges
>
> Hello,
>
> We cannot tell you what's wrong with your code without showing us a *small*
> example that demonstrates the problem.
>
> T.
>
> On 11/18, patricia wrote:
> > I am creating a weighted and undirected graph as follows:
> > - Draw two vertices randomly and make the connection between them, with a weight value that is stored in an array in assorted positions. The values that are stored in this matrix are unchanged.
> > For example, the sorteei positions 10 and 15 will in the weight matrix on the line 10 and column 15, the value stored in that position will be the weight of edge 10 --- 15.
> > But my code is generating multiple edges, so I'm using the igraph_simplify (& net, 1,1, & edge_comb) with igraph_attribute_combination attribute (& edge_comb, "weight", IGRAPH_ATTRIBUTE_COMBINE_FIRST, IGRAPH_NO_MORE_ATTRIBUTES) function to eliminate them. But I want the value of the weights remain unchanged; but even using the above attribute (COMBINE_FIRST) weights are changing. What can I do to correct this error?
> >
> > Thank you
>
> > _______________________________________________
> > igraph-help mailing list
> > address@hidden
> > https://lists.nongnu.org/mailman/listinfo/igraph-help
>
>
> --
> T.
>
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