Re: [igraph] igraph_spmatrix_t and graphs

[Tamas Nepusz]

Dear Oscar,

igraph_spmatrix_t is more like an internal datatype than a full-fledged
sparse matrix type, so not all operations are supported or documented; for
instance, there is no simple one-function call to construct a graph from an
igraph_spmatrix_t.

One thing that is not documented but may be useful for you is an auxiliary
data type called igraph_spmatrix_iter_t, which is an iterator over the
possibly non-zero entries of the sparse matrix. You can use an
igraph_spmatrix_iter_t to construct an edge list and a corresponding weight
vector on the fly, then create an igraph_t out of the edge list, and assign
the weights as edge attributes. These are the igraph_spmatrix_* functions
from the header:

int igraph_spmatrix_iter_create(igraph_spmatrix_iter_t *mit, const
igraph_spmatrix_t *m);
int igraph_spmatrix_iter_reset(igraph_spmatrix_iter_t *mit);
int igraph_spmatrix_iter_next(igraph_spmatrix_iter_t *mit);
igraph_bool_t igraph_spmatrix_iter_end(igraph_spmatrix_iter_t *mit);
void igraph_spmatrix_iter_destroy(igraph_spmatrix_iter_t *mit);

So, first you create an iterator using igraph_spmatrix_iter_create, then
step over the elements one by one using igraph_spmatrix_iter_next, and check
whether you are at the end of the matrix using igraph_spmatrix_iter_end.
Finally, you destroy the iterator using igraph_spmatrix_iter_destroy. At any
stage, you can look up the current row index, column index and value using
the "ri", "ci" and "value" members of the iterator.

Cheers,
Tamas

On 08/05/2011 04:20 PM, Oscar Cuadros Linares wrote:
> Dear Igraph users.
> 
> I want to create a graph from a sparse matrix (igraph_spmatrix_t), but i 
> can't. 
> sugestions?
> Thanks.
> Oscar
> 
> -- 
> En Cristo y María
> 
> Oscar Cuadros Linares
> Ciencia de la Computación
> 
> 
> 
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