Hi Keeler,
On Wed, Jul 25, 2012 at 05:14:41PM -0700, Keeler Russell wrote:
> I've been working on a function to calculate the chromatic symmetric
> function (a.k.a. CSF) of a graph as part of a related research project.
> You can find the code here: https://github.com/keeler/csf (the files are
> csf.py and csf.pyx, in particular). I wanted to know if this function
> would be useful to anyone, and would greatly appreciate any tips regarding
> how to improve its performance.
>
> Notes on the algorithm: I use Thm 2.5 from Stanley's "A Symmetric Function
> Generalization of the Chromatic Polynomial of a Graph" to calculate the
> CSF. This is pretty directly reflected in the code in csf.py. However,
> csf.pyx uses a bit more machinery. First of all, it stores the
> coefficients of the corresponding power-sum symmetric function terms in a
> dictionary of speedy access. Second, I represent the elements in each edge
> set with a bitset (1 for included, 0 for excluded). Third, I use Gray
> Codes to either add or delete a single edge for each iteration.
>
> If you have any questions for me, or would like me to provide more
> comments in my code (which I may just do anyway), please feel free to ask
> me.
As Frédéric said, this sounds like a nice addition indeed! At this
point, I haven't looked at your code; so the following comment might
not be relevant: the internal data structure for symmetric functions
is really a dictionary partition->coefficient; so you might want to
directly manipulate a symmetric function rather than a dictionary.
Good luck with getting through your first contribution! Please ask if
you get stuck. For info: the main Sage developers working on graphs
(Nathann Cohen) is traveling in the wild until the end of August; so
you will probably get more feed back later on.
Best regards,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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