ASKSAGE: Sage Q&A Forum - RSS feedhttps://ask.sagemath.org/questions/Q&A Forum for SageenCopyright Sage, 2010. Some rights reserved under creative commons license.Mon, 16 Jul 2018 15:58:37 +0200Path between representatives and normal forms in Coxeter groupshttps://ask.sagemath.org/question/43036/path-between-representatives-and-normal-forms-in-coxeter-groups/Hello everyone, I would like to find a way to compute a chain of rewriting move between two reduced representative of the same word in a Coxeter group.
As I work only with A,D,E groups, the only rewriting move I need are commutation ($s_i s_j=s_j s_i$) and braid moves ($s_i s_j s_i=s_j s_i s_j$).
For example, in Coxeter Group of type $A_3$ : $\langle s_1,s_2,s_3|s_i^2=1\ ,\ s_1s_2s_1=s_2s_1s_2\ ,\ s_2s_3s_2=s_3s_2s_3\ ,\ s_1s_3=s_3s_1 \rangle $ given the representative $\mathbf{i}=[1,2,3,2,1] $ i can reach the representative $\mathbf{i}'=[3,2,1,2,3]$ by a braid move on 2,3,2, then commutations between 1 and 3 and eventually a braid move on 1,2,1.
I thought than such an algorithm already existed but I was unable to find it so I decided to write it by myself, in a surely very unnefficient way : given a normal form algorithm, compute the moves from $\mathbf{i}$ to the normal form, then the moves from $\mathbf{i}'$ to the normal form and then deducing a path from $\mathbf{i}$ to $\mathbf{i}'$ (not the shortest I think, but at this moment efficiency questions are not very relevant to myself). In order to do so, I would like to know how coxeter words are implemented in Sage as it seems to me that when you ask `w.reduced_word()` it gives you the maximum representative for lexicographic ordering, does it have a table of all the representative ? Or does it use a normal form algorithm ?
EtienneMénardMon, 16 Jul 2018 15:58:37 +0200https://ask.sagemath.org/question/43036/