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

From: Szabolcs Horvát
Subject: Re: [igraph] why use floating point for graph nodes?
Date: Thu, 5 Nov 2015 10:12:14 +0100

Hi Gabor,

Just out of curiosity, have you measured what sort of performance
impact that change had, if any?


On 5 November 2015 at 10:08, Gábor Csárdi <address@hidden> wrote:
> FYI: https://github.com/igraph/igraph/tree/feature-int-igraph_t
> Gabor
> 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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