#17982: Ambient space root poset is broken
-------------------------------------+-------------------------------------
       Reporter:  nathanwilliams     |        Owner:
           Type:  defect             |       Status:  needs_review
       Priority:  major              |    Milestone:  sage-6.6
      Component:  combinatorics      |   Resolution:
       Keywords:  root poset,        |    Merged in:
  days64                             |    Reviewers:  Nicolas M. ThiƩry
        Authors:  Nathan Williams    |  Work issues:
Report Upstream:  N/A                |       Commit:
         Branch:  public/17982       |  c1c9fd5f1d9863852075aa79022c0e7e812ad28c
   Dependencies:                     |     Stopgaps:
-------------------------------------+-------------------------------------
Description changed by nathanwilliams:

Old description:

> The ambient space for the root system of type A causes a bug in the
> method root_poset().  In particular, the following code causes an error.
>
>   sage: RootSystem(['A', 2]).ambient_space().root_poset()
>   Error in lines 2-2
> Traceback (most recent call last):
>   File "/projects/35ffe4a3-aac4-4456-85aa-
> 5c0ad4b5e2d1/.sagemathcloud/sage_server.py", line 875, in execute
>     exec compile(block+'\n', '', 'single') in namespace, locals
>   File "", line 1, in <module>
>   File "/usr/local/sage/sage-6.5/local/lib/python2.7/site-
> packages/sage/combinat/root_system/root_lattice_realizations.py", line
> 1050, in root_poset
>     root_cover = root + simple_roots[i]
>   File "/usr/local/sage/sage-6.5/local/lib/python2.7/site-
> packages/sage/sets/family.py", line 718, in __getitem__
>     return self._dictionary.__getitem__(i)
> KeyError: 3
>
> I fixed this bug by redefining the dimension to be the number of simple
> roots.

New description:

 The ambient space for the root system of type A causes a bug in the method
 root_poset().  In particular, the following code causes an error.

   sage: RootSystem(['A', 2]).ambient_space().root_poset()
   Error in lines 2-2
   KeyError: 3

 I fixed this bug by redefining the dimension to be the number of simple
 roots.

--

--
Ticket URL: <http://trac.sagemath.org/ticket/17982#comment:4>
Sage <http://www.sagemath.org>
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