Re: [igraph] igraph_matrix_copy_to()

[Fernando Martinez]

Hi Gábor and Tamas,

I've solved it like this:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

#include <igraph.h>

int main(){

  
   igraph_neimode_t mode = IGRAPH_ALL;
   igraph_matrix_t matriz;
   igraph_vs_t from;


   double distances_vector[numberofnodes*numberofnodes];
   long distances[numberofnodes][numberofnodes];

   igraph_vs_all(&from);


   igraph_matrix_init(&matriz, numberofnodes, numberofnodes);

   //get the shortest paths:
   igraph_shortest_paths(&graph, &matriz, from, mode);


   //copy the shortest paths to a 'double' single-dimensioned array:
   igraph_matrix_copy_to(&matriz, distances_vector);




   //transform the single-dimension array into matrix form for convenience:
   for(j=0; j<numberofnodes; j++){
     for(m=0; m<numberofnodes; m++){
       distances[j][m]=(long)distances_vector[numberofnodes*j+m];
     }
   }



   igraph_matrix_destroy(&matriz);
   igraph_vs_destroy(&from);

   return(0);

}


@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

This works fine. Thanks very much for your inputs.

Cheers,
Fernando





Gábor Csárdi wrote:
> Tamas,
>
> you are right, this is one thing. But even if it is igraph_real_t the
> compiler gives a warning (gcc) or error (g++), because
> igraph_matrix_copy_to expects a pointer to a real, and not a pointer
> to an array. See e.g.
> http://www.lysator.liu.se/c/c-faq/c-2.html#2-10
>
> Fernando, consider using a pointer to the first element of the array
> instead of a pointer to an array. I think this can be done by a simple
> casting, although I might miss something here, pointers to arrays are
> tricky. Also, I don't know whether using g++ instead of gcc changes
> anything here, except for getting an error instead of a warning.
>
> But actually, why copying the thing anyway? What is wrong with keeping
> it in an igraph_matrix_t?
>
> Best,
> Gabor
>
> On Mon, Jun 28, 2010 at 8:22 PM, Tamas Nepusz <address@hidden> wrote:
>   
> > Hi Fernando,
> >
> > igraph matrices store real numbers, not integers, therefore long is not a 
> > suitable data type for igraph_matrix_copy_to. Use an array of igraph_real_t 
> > instead:
> >
> > igraph_real_t distances[numberofnodes][numberofnodes];
> >
> > --
> > Tamas
> >
> > On 2010.06.28., at 18:44, Fernando Martinez wrote:
> >
> >     
> > > Dear All,
> > >
> > > I'm having problems when using the function igraph_matrix_copy_to()
> > >
> > > As I understand it, this function allows to copy an igraph matrix into a normal 
> > > C matrix. However, I get an error when compiling.
> > >
> > > My code is the following:
> > >
> > > @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
> > >
> > >
> > >
> > > #include <igraph.h>
> > >
> > > int main()
> > > {
> > >
> > >
> > >       igraph_matrix_t matriz;
> > >       igraph_vector_t vec;
> > >       igraph_vs_t from;
> > >       igraph_neimode_t mode = IGRAPH_ALL;
> > >
> > >       long numberofnodes=512;
> > >
> > >       long distances[numberofnodes][numberofnodes];
> > >
> > >       igraph_vs_all(&from);
> > >
> > >       igraph_shortest_paths(&graph, &matriz, from, mode);
> > >
> > >       igraph_matrix_copy_to(&matriz, distances);
> > >
> > >       return(0);
> > >
> > > }
> > >
> > >
> > > @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
> > >
> > > I compile in Unbuntu 9.04
> > >
> > > g++ -I/igraph -L/lib w1024.cpp -ligraph -lgsl -lgslcblas -o w1024
> > >
> > > and gives error for the line of "igraph_matrix_copy_to(&matriz, distances);":
> > >
> > > error: cannot convert `long int (*)[((long unsigned int)((long 
> > > int)numberofnodes))]' to `igraph_real_t*' for argument `2' to `int 
> > > igraph_matrix_copy_to(const igraph_matrix_t*, igraph_real_t*)'
> > >
> > > Any ideas on how to pass the data from the igraph matrix to a C matrix?
> > >
> > >
> > > Cheers,
> > > Fernando
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > _______________________________________________
> > > igraph-help mailing list
> > > address@hidden
> > > http://lists.nongnu.org/mailman/listinfo/igraph-help
> > >       
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> >
> >     
>
>
>
>