SymmetricGroup's "in" and ".contains", and reason for working a certain way

[Gaurav Dhingra]

Hi everyone

>>> from sympy.combinatorics.named_groups import SymmetricGroup
>>> s_4 = SymmetricGroup(4)           # symmetricGroup of order 4

>>> p = Permutation(1, 2, 3)
>>> p in s_4
False

>>> s_4.contains(p)
True

Regarding my second question:
I am aware that contrary to GAP, which makes Groups like a little differently
>>> s_4 = SymmetricGroup(4)
>>> s_4.is_group
False

while in GAP
gap> s_4:= SymmetricGroup(4)
gap> IsGroup(s_4)
True

Is there any reason for why things work this way? Is thought to have some benefit contrary to how GAP defines it?

Gaurav Dhingra (gxyd)

[Aaron Meurer]

On Thu, Dec 10, 2015 at 7:03 AM, Gaurav Dhingra <axyd...@gmail.com> wrote:
> Hi everyone
>
>>>> from sympy.combinatorics.named_groups import SymmetricGroup
>>>> s_4 = SymmetricGroup(4) # symmetricGroup of order 4
>
>>>> p = Permutation(1, 2, 3)
>>>> p in s_4
> False
>
>>>> s_4.contains(p)
> True

I'm guessing this is a bug. It's probably related to the weirdness of
the group API (see below).

>
> Regarding my second question:
> I am aware that contrary to GAP, which makes Groups like a little
> differently
>>>> s_4 = SymmetricGroup(4)
>>>> s_4.is_group
> False
>
> while in GAP
> gap> s_4:= SymmetricGroup(4)
> gap> IsGroup(s_4)
> True
>
> Is there any reason for why things work this way? Is thought to have some
> benefit contrary to how GAP defines it?

This API seems really weird to me. It seems there is a distinction
between a group that is completely generated and a group that is just
generators. I don't think it's a good design, since the name of the
object is PermutationGroup, I would expect it to always represent a
group. At the very least, it shouldn't use the term "is_group" to
determine if the object's elements have been completely generated or
not.

Aaron Meurer

>
> Gaurav Dhingra (gxyd)
>
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