#12912: Interface to Fokko Ducloux's Coxeter 3
---------------------------------+------------------------------------------
Reporter: nthiery | Owner: sage-combinat
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-5.7
Component: combinatorics | Resolution:
Keywords: coxeter | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Mike Hansen | Merged in:
Dependencies: | Stopgaps:
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Comment (by nthiery):
Replying to [comment:6 aschilling]:
> {{{
> sage: from sage.libs.coxeter.co
> sage.libs.coxeter.coxeter sage.libs.coxeter.coxeter_group
> sage: from sage.libs.coxeter.coxeter import get_CoxGroup as CoxGroup
> sage: W = CoxGroup(['A',1])
> sage: W.bruhat_interval([],[])
> [[]]
> sage: W = CoxGroup(['A',2])
> }}}
Investing further,
bruhat_interval explicitly destructs the C++ list which is defined
earlier in this method and passed to Coxeter3's {{{interval}}} function.
Is
it really needed? If we comment it out, there is no more segfault. So
the destruction must somehow corrupt Coxeter3's internal state (though
it's strange that the segfault occurs upon constructing a new group)
Some evidence why it might not be needed:
- It's a list, not a reference to a list; so c++ should destruct it at
the end of the function, right?
- Assignment/copy operators seem to be appropriately defined in
Coxeter3 for CoxWord element to be put in a list and be destructed
properly.
- The pointcare_polynomial does very similar things but does not call
this destructor at the end (so at least one of the two is wrong).
- There does not seem to be a memory leak when one comments out the
destructor, at least not after the third call:
{{{
sage: sage: from sage.libs.coxeter.coxeter import CoxGroup as CoxGroup
sage: W = CoxGroup(['A',7])
sage: w0 = WeylGroup(['A',7]).long_element().reduced_word()
sage: sage.misc.getusage.get_memory_usage(t=None)
sage: 911.23046875
sage: len(W.bruhat_interval([], W(w0)))
40320
sage: sage: sage.misc.getusage.get_memory_usage(t=None)
5972.0
sage: len(W.bruhat_interval([], W(w0)))
40320
sage: sage.misc.getusage.get_memory_usage(t=None)
5973.50390625
sage: len(W.bruhat_interval([], W(w0)))
40320
sage: sage.misc.getusage.get_memory_usage(t=None)
5973.50390625
sage: len(W.bruhat_interval([], W(w0)))
40320
sage: sage.misc.getusage.get_memory_usage(t=None)
5973.50390625
}}}
This is confirmed by looking at the processus memory usage.
Altogether, I guess I vote for commenting out the questionable
destructor call, and consider the issue as resolved for now. We will
see later if any issue arises once we put Coxeter 3 to heavy use.
Mike, what do you think?
Cheers,
Nicolas
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12912#comment:8>
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