#14492: Modular group cohomology, version 2.1.4
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Reporter: SimonKing | Owner: tbd
Type: defect | Status: positive_review
Priority: major | Milestone: sage-5.10
Component: packages: optional | Resolution:
Keywords: group cohomology | Work issues:
Report Upstream: N/A | Reviewers: Volker Braun
Authors: SimonKing | Merged in:
Dependencies: | Stopgaps:
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Comment (by SimonKing):
Replying to [comment:26 vbraun]:
> Do you actually need anything fancy from the SGL or just the list of the
first N groups?
I guess the main reason for using it is: Get a concise identifier of a
group with a fixed set of generators.
If I want to know the cohomology of a group G, then I need to consider
restrictions to "interesting" subgroups: Maximal p-elementary abelian
subgroups; Sylow p-subgroup; normalizer in G of the centre of a Sylow
p-subgroup; intersection of two conjugates of a Sylow p-subgroup; ...
If I know the small groups library address of the interesting group, then
I can easily look up in my data base whether the cohomology of this
particular group has already been computed. Otherwise, I needed to compute
the cohomology of multiple isomorphic copies of one group repeatedly.
Mathematically, it would of course be possible to lift the dependency on
the small groups library. In fact, if the address in the small groups
library can not be found, then a "descriptive" name (that describes the
construction of this group) is chosen to access the data base. So, in
these cases, my code is independent of the small groups libary.
Making it totally independent would require...
* to rewrite a couple of constructions; this would, in particular, be
needed if the use of the small groups library should become optional.
* to totally rewrite the code that accesses my data bases; but actually I
would like to use a "real" data base (sql?), so that rewriting will sooner
or later be needed anyway.
* to rewrite almost ''all'' doctests. Since all functions and methods are
tested, this would be a long and very annoying task.
> The `spkg_install` looks good to me.
So, there is no reason why I saw it happily continue to install the
package after a compilation error? Strange.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14492#comment:27>
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