Re: [igraph] Comparing large graphs

[Charles Novaes de Santana]

Thank you again, Tamás. You were absolutely right about my mistake in
printing the matrix. I did a simple cast and my matrix operations
worked fine.

But I still have problems with the "infinity" given by the
shortest_paths function. I did the function you suggested me (to
replace all IGRAPH_INFINITY by zeros), but I have problems in the
calculation of the shortest paths itself, before I have the
opportunity to replace the "inifinity" by "zero".

If you don't mind, I am sending attached to this message a small
program with the part of my code where I got the error. And an example
of a network I am studying. Maybe it is an error in the format of my
network and I can not understand it yet. Or maybe it is because my
network is very sparse.

Thank you very much for your attention,

Best,

Charles

/*SOURCE CODE*/

#include<igraph.h>

int main(void){
        igraph_t g1;
        igraph_matrix_t l1;
        igraph_vs_t vertices;

        int i,j;
        FILE *ifile1;

/*Reading the network*/
        ifile1=fopen("./network.net", "r");
        if (ifile1==0) {return 10;}
        igraph_read_graph_pajek(&g1, ifile1);
        fclose(ifile1);

/*Initializing the matrix l1 and the vector of vertices*/

        igraph_vs_all(&vertices);
        igraph_matrix_init(&l1, 0, 0);

/*Calculating the shortest paths*/

igraph_shortest_paths(&g1,&l1,vertices,vertices,IGRAPH_ALL);

/*Desconstructors*/
        igraph_matrix_destroy(&l1);
        igraph_vs_destroy(&vertices);
        igraph_destroy(&g1);
        return;
}


        igraph_matrix_destroy(&l1);
        igraph_vs_destroy(&vertices);
        igraph_destroy(&g1);


On Wed, Dec 5, 2012 at 10:32 AM, Tamás Nepusz <address@hidden> wrote:
>> First, I was wondering if Igraph considers IGRAPH_INFINITY as zero or
>> as other value.
> IGRAPH_INFINITY is infinity, period. It is there only to provide us with a 
> sort-of-platform-independent way to refer to infinity.
>
>> I am working with shortest-paths matrices and I would
>> like the distance between two vertices that can not reach each other
>> to be zero.
> Well, you have to check all the cells in the matrix and if a cell is equal to 
> IGRAPH_INFINITY, you have to set it to  zero.
>
>> (I tryied to do "igraph_matrix_scale(matrix,1./2)" and it gave
>> me a zero-matrix).
> Theoretically it should work; there is no limitation on igraph_matrix_scale 
> to work on integer values only. I have just tested it on my machine and it 
> worked for me, so I guess that the error is somewhere else; for instance, in 
> the way you print the values.
>
> Cheers,
> --
> T.
>
>
> _______________________________________________
> igraph-help mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/igraph-help



-- 
Um axé! :)

--
Charles Novaes de Santana
http://www.imedea.uib-csic.es/~charles
PhD student - Global Change
Laboratorio Internacional de Cambio Global
Department of Global Change Research
Instituto Mediterráneo de Estudios Avanzados(CSIC/UIB)
Calle Miquel Marques 21, 07190
Esporles - Islas Baleares - España

Office phone - +34 971 610 896
Cell phone - +34 660 207 940

network.net
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