#13365: Add Semidirect Product Method for Permutation Groups
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Reporter: khalasz | Owner: joyner
Type: enhancement | Status: needs_review
Priority: minor | Milestone: sage-5.3
Component: group theory | Resolution:
Keywords: groups semidirect product GAP | Work issues:
Report Upstream: N/A | Reviewers: Benjamin
Jones
Authors: Kevin Halasz | Merged in:
Dependencies: | Stopgaps:
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Changes (by benjaminfjones):
* keywords: => groups semidirect product GAP
* reviewer: => Benjamin Jones
Comment:
Look great! A couple of comments to start:
* Line 92 `sage/categories/groups.py`: I think the exception message
would be more clear if we just say something like "semidirect prodcuct of
%s and %s is not yet implemented."
* Line 1762 `sage/groups/perm_gps/permgroup.py`: I think it would be
clearer here to say that `N` is a group which acted on by `self` and which
is isomorphic to a normal subgroup of the semidirect product.
* Line 1803: "where it is generally thought that" --> "where, by
convention,"
* Line 1870: The three tests at the beginning of the method are a good
measure, but I wonder if they pose too large a computational cost when the
input groups are large? Have you tried constructing any large semidirect
products with your code? I would be interested to see how much overhead
the three checks cost.
One thing you could do is add an optional parameter, something like
`check=True` that defaults to True, but if the user sets it to False then
the three checks aren't done and the user takes full responsibility if,
e.g. the supplied list of elements of `self` does not generate `self`.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13365#comment:6>
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