#11187: Implementation of finite reflection groups
-------------------------------------+-------------------------------------
Reporter: stumpc5 | Owner: tbd
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-7.2
Component: combinatorics | Resolution:
Keywords: reflection group, | Merged in:
days49, days 64.5 | Reviewers:
Authors: Christian Stump | Work issues:
Report Upstream: N/A | Commit:
Branch: public/11187 | def701588736edda81a86ddd1a9cbdbc849657be
Dependencies: #20107 | Stopgaps:
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Comment (by tscrim):
Replying to [comment:210 stumpc5]:
> Travis, could you have a look at the diffset 8497f5d; I commented out
that the change is actually used, see {{{#for i in self.noncom[first]}}},
it seems to slow down the test even though much less is actually tested.
Maybe you see how to get rid of the overhead the line {{{for i in
self.noncom[first]}}} has compared to {{{for i in
range(first+1,self.n)}}}.
My guess is because Cython is smart enough to translate
{{{#!python
for i in range(n)
}}}
into
{{{#!c
for(i=0; i<n; ++i)
}}}
whereas for the other, it is iterating over some object (which, a priori,
may not even be iterable). In more detail, Cython doesn't even know that
it is iterating over a list, just that `self.noncom` is. Try:
{{{#!python
nc = self.noncom[first]
for i in nc:
}}}
or the variant
{{{#!python
nc = self.noncom[first]
k = len(nc)
for dummy in range(k):
i = nc[dummy]
}}}
where you have `cdef list nc` and `cdef int dummy, k` (although I suspect
the former of these is faster).
--
Ticket URL: <http://trac.sagemath.org/ticket/11187#comment:212>
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