Hello,
Let me advertise a patch on #8044 which introduces categories in the
group code and uses it to do some cleanup. There are some minor design
questions which I thought should be brought up here. This is a
followup to #7921, and I'd love to see it in 4.3.2.
Thanks in advance for feedback and review!
Cheers,
Nicolas
Categories for finite/permutation/symmetric groups
http://trac.sagemath.org/sage_trac/ticket/8044
Ticket description:
* Introduces two new categories: FiniteGroups? and
FinitePermutationGroups?
* Puts all permutation groups and some other finite groups in the
corresponding categories. There remains to handle finite matrix
groups and Galois groups in sage/rings/number_field/.
* As a result, this standardizes the interface of those groups
(cardinality, one, ...).
* Deprecates the class sage.groups.group.FiniteGroup. Content
moved to the SemiGroups / FiniteGroups categories
* Merges cayley_graph with that for FiniteSemigroups. In the
merging, connecting_set was deprecated to generators. Also
providing a single element by itself as connecting set is no
more supported. Finally the default is side = "right" (was
"twosided" for semigroups). This method is also generalized to
Semigroups with an elements option (should this be vertices?).
Why do we care about the produced graph using implementation =
"networkx"? I would tend to remove this implementation detail;
this would change the order of the edges, which requires fixing
a test in sage.graphs.generic_graphs
* Provides group_generators defined from gens, as well as
semigroup_generators defined from group_generators in the finite
and coxeter cases.
* Also puts the SymmetricGroup in the FiniteWeylGroups category.
Beware: unusual product convention
Beware: this changes the generators to the standard Weyl group
generators, that is the elementary transpositions
* Adds an has_descent method to permutation group elements
* Make all named permutation groups have UniqueRepresentation
* Questionable: the underlying set of an alternating or symmetric
group is now a tuple. This is safer and helps
UniqueRepresentation. However, this could break backward
compatibility. Also, maybe we want to keep the output as
SymmetricGroup([1,3,4])?
* Makes more systematic use of TestSuite(...).run()
* Makes a minor improvement to FiniteEnumeratedSets tests for
large finite enumerated sets
* Strips away unused imports
* Updates a couple doctests here and there
Nicolas
--
Nicolas M. Thiéry "Isil" <[email protected]>
http://Nicolas.Thiery.name/
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