#20477: reduced words in complex reflection group
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       Reporter:  stumpc5                        |        Owner:
           Type:  enhancement                    |       Status:  new
       Priority:  major                          |    Milestone:  sage-7.2
      Component:  combinatorics                  |   Resolution:
       Keywords:  complex reflection groups,     |    Merged in:
  reduced words                                  |    Reviewers:
        Authors:                                 |  Work issues:
Report Upstream:  N/A                            |       Commit:
         Branch:                                 |     Stopgaps:
   Dependencies:                                 |
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Comment (by stumpc5):

 The typical ways of getting elements in the group are

     1. iterating through the group
     2. "from_reduced_word" and "from_reduced_word_in_reflections"
     3. getting special elements such as "a_coxeter_element"

 I believe whenever we know a reduced word Red(w) (in simples S or in all
 reflections R) *a priori*, we should store that information.

 concerning 1)

     - if the user is interested in Red_S(w), then she should use an
 iterator that generates the group (as we already do) breadth first from S,
 and store all Red_S(w) along the way. Similarly for R: if you are
 interested in Red_R(w), you should use a breadth first iterator from R and
 store all Red_R(w).
     - this way, you get the info you want from the iterator for free
 without actually computing a reduced word from scratch.

 concerning 2) same as for 1, store info you have, and only compute the
 other. This might be a problem (in case you give a word is S/R and want a
 word in R/S), but you usually do not create tons of elements from words.

 concerning 3) in this case, it is likely that you have to compute words
 explicitly.

 Overall, I think the most common case will be (1) and we can treat that
 without actually computing reduced words.

--
Ticket URL: <http://trac.sagemath.org/ticket/20477#comment:1>
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