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Re: [igraph] why use floating point for graph nodes?

From: Gábor Csárdi
Subject: Re: [igraph] why use floating point for graph nodes?
Date: Thu, 5 Nov 2015 09:08:55 +0000

FYI: https://github.com/igraph/igraph/tree/feature-int-igraph_t


On Wed, Nov 4, 2015 at 11:12 PM, Tamas Nepusz <address@hidden> wrote:
> Ah, sorry, just realized that igraph_t contains igraph_vector_t
> objects, and those indeed contains doubles. Yes, you are right, this
> is weird, and this is a heritage from the old days when
> igraph_integer_t was also typedef'd to a double. Just for fun I have
> changed the types in igraph_t to igraph_vector_long_t and made a few
> quick modifications to src/type_indexededgelist.c to make things
> compile without warnings, and it seems to do the trick - all tests
> compile just fine. However, there are probably lots of unnecessary
> casts left in the code, and of course we cannot change the public API
> (which still uses igraph_vector_t in lots of cases to store vertex
> lists) without breaking everyone else's code, so this quirk is
> probably here to stay for while (unless Gabor makes an executive
> decision and decides to break the API intentionally).
> If anyone is interested in it, I have pushed the changes into a
> separate branch named feature/graph_t-with-long-vector.
> T.
> T.
> On Wed, Nov 4, 2015 at 11:18 PM, Tamas Nepusz <address@hidden> wrote:
>>> Why does igraph use floating point data (C doubles) to represent graph
>>> vertices?  It seems like an unusual choice and I would expect it to
>>> negatively affect performance.  Is it an R heritage?
>> Errrrm... it used to be that way a (not so) long time ago; see this
>> thread on the mailing list:
>> https://lists.nongnu.org/archive/html/igraph-help/2009-01/msg00119.html
>> However, I have just checked the source code and igraph_integer_t is
>> now typedef'd to an int so this is probably not the case any more.
>> T.
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