Re: [igraph] Dose the index of vertices in a graph start from 0?

[Gábor Csárdi]

On Thu, Sep 15, 2011 at 4:27 AM, Minh Nguyen <address@hidden> wrote:
> Hi,
>
> On Thu, Sep 15, 2011 at 6:23 PM, Zhijiang Wang
> <address@hidden> wrote:
>> Thanks!
>> why is the 0-starting index is used?
>
> In computer science, our indices start from zero. In mathematics,
> indices start from one. Graph theory as treated by igraph is
> considered computer science. And people who develop igraph are
> computer scientists.

Another reason for the 0-based indexing was that igraph internals are
written in C, and C uses 0-based indices for arrays, so it was natural
(for a computer scientist at least) to go with that. Keeping the
zero-based indexing in R simplified a lot of things, and made igraph
somewhat faster.

Soon I realized that 0-based in indices are causing problems in R.
This will be only corrected in the coming 0.6 version, where vertices
are indexed from 1 (if you use igraph from R). This also means that
existing code will no longer be compatible with the new 0.6 version,
unfortunately.

Best,
Gabor

>> 于 2011-9-15 16:19, Minh Nguyen 写道:
>>
>> Hi,
>>
>> 2011/9/15 Zhijiang Wang <address@hidden>:
>>
>> Dear all,
>>
>> I used the function maximal.cliques, and found the smallest index of
>> vertices is 0.
>> So, dose the index of vertices in a graph start from 0?
>>
>> Yes.
>
> --
> Regards
> Minh Van Nguyen
>
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>



-- 
Gabor Csardi <address@hidden>     MTA KFKI RMKI