[GAP Forum] CoxIter - Computing invariants of hyperbolic Coxeter groups

Christopher Jefferson caj21 at st-andrews.ac.uk
Thu Sep 1 17:21:59 BST 2016


Hi,

I installed the package on a mac, and checked it built / ran correctly. Everything seemed reasonable. I can’t really comment on the maths, but some minor comments:

* There are a few practice functions (CoxIter_Example, CoxIter_Compute) which I assume you don’t need, that need cleaning up.

* Be sure to handle the program failing (for example, if you pass it excessively large integers).

* In CoxIterCompute, just do ‘SetCofinite(ci, EvalString(data[2]))’. This avoids another function call when you want these values later, and also sets ‘HasCofinite’ to true.

So for example Cofinite could be:

InstallMethod( Cofinite,
	"for hyperbolic Coxeter groups", 
	[IsCoxIter and IsCoxIterRep], 
	function(obj)
		CoxIterCompute(obj);
		if HasCofinite(obj) then
       return Cofinite(obj);
else
       return fail;
       fi;
	end);



On 01/09/2016, 16:14, "forum-bounces at gap-system.org on behalf of Rafael Guglielmetti" <forum-bounces at gap-system.org on behalf of rafael at rgug.ch> wrote:

    
    Dear GAP users,  
    I few months ago, I released CoxIter, a program to compute invariants of hyperbolic Coxeter groups (Euler characteristic, f-vector of the associated polyhedron, growth series and growth rate, cocompactness and cofiniteness test).  
    More information can be found here: [https://coxiter.rgug.ch/](https://coxiter.rgug.ch/) and [https://github.com/rgugliel/CoxIter](https://github.com/rgugliel/CoxIter)  
      
    More recently, it was suggested to create a GAP package with CoxIter.  
      
    I have a preliminary version of the package and before I wrap this and write a proper documentation, I would like some feedback from GAP users/contributors to know whether the interface is nice to use, if the names of the  function are standard, if the "architecture" of the package is not stupid, ...  
      
    The package, together with an example can be found here: [https://github.com/rgugliel/CoxIterGAP](https://github.com/rgugliel/CoxIterGAP)  
      
    I would be happy to get any feedback. Also, if you get trouble  
    building/using it, feel free to contact me.  
      
    Thanks a lot.  
      
    Best,  
      
    Rafael  
    
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