Re: [igraph] Simple random tree generation

[christophe laferriere]

Perfect, it works like a charm!

Thanks again!

Le 27 déc. 2010 à 21:48, Tamás Nepusz a écrit :

>> I'm new to igraph and I'm looking to create random tree with 0 to 4 sons for 
>> each node for example.
>> I was wondering if this is possible with igraph
> Yes, it is, but most of the hard work must be done by you and not by igraph 
> (as igraph can only generate regular trees as a built-in function). 
> Basically, you have to generate the edge list yourself and then pass it to 
> igraph_create.
> 
> Something like this (totally untested, but you get the idea):
> 
> 
> int create_tree(igraph_t* graph, int desired_number_of_non_leaf_nodes, int 
> min_children, int max_children) {
>  igraph_vector_t edgelist;
>  int next_parent = 0, next_child = 1, i;
> 
>  igraph_vector_init(&edgelist, 0);
> 
>  while (next_parent < desired_number_of_non_leaf_nodes) {
>    int num_children = rand() % (max_children - min_children + 1) + 
> min_children;
> 
>    if (next_parent >= next_child) {
>      /* You may simply break out of the loop here instead of printing an 
> error */
>      IGRAPH_ERROR("ran out of potential parent nodes", IGRAPH_EINVAL);
>    }
> 
>    for (i = 0; i < num_children; i++) {
>      IGRAPH_CHECK(igraph_vector_push_back(&edgelist, next_parent));
>      IGRAPH_CHECK(igraph_vector_push_back(&edgelist, next_child));
>      next_child++;
>    }
> 
>    next_parent++;
>  }
> 
>  igraph_create(graph, edgelist, 0, 0);
> 
>  return IGRAPH_SUCCESS;
> }
> 
> Usage:
> 
> igraph_t graph;
> 
> srand(time(0));
> create_tree(&graph, 123, 0, 4);
> 
> -- 
> Tamas
> 
> 
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--
Chris.