#17979: Reimplementation of IntegerListsLex
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Reporter: aschilling | Owner:
Type: defect | Status: needs_work
Priority: blocker | Milestone: sage-6.6
Component: combinatorics | Resolution:
Keywords: days64 | Merged in:
Authors: Bryan Gillespie, | Reviewers:
Anne Schilling, Nicolas M. Thiery | Work issues: support n in an
Report Upstream: N/A | iterable
Branch: | Commit:
public/ticket/17979 | cb18ced22db714063e744bb907a035b4fe3afa24
Dependencies: | Stopgaps:
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Comment (by bgillespie):
Replying to [comment:48 jdemeyer]:
> I dislike the fact that the warning shows even in cases where the output
is obviously finite:
> {{{
> sage: IntegerListsLex(5, ceiling=lambda i:i, length=5)
> /usr/local/src/sage-config/local/lib/python2.7/site-
packages/sage/combinat/integer_list.py:606: UserWarning: When the user
specifies a method, then (s)he is responsible that the algorithm
> will not hang. Also note that the specified function should
start at 0 rather than 1.
> Before trac#17979 the indexing was ambiguous and sometimes
started at 1.
> Before trac#17979 the indexing was ambiguous and sometimes started at
1.""")
> Integer lists of sum 5 satisfying certain constraints
> }}}
>
> Also note that the formatting of the warning is not quite right.
I updated the formatting of the warning (also the message to be more
explicit/verbose), so check if it looks reasonable to you.
Here's what our thought process was concerning when to raise a warning
message. We could easily do some additional computations to find certain
cases where the specified parameters make giving a custom function safe.
However, one of the complaints with the old version was that it was
difficult to understand how the parameters affected the output. If we
make it "sometimes" verifiably safe to use a custom function, depending on
the circumstances, then that's another point of complexity for the user to
follow--but if we just raise a warning whenever a user uses a custom floor
or ceiling function (but only if they haven't "signed a waiver" by
specifying `waiver=True`), that simplifies the interface for the user.
Also note that the example you gave could be handled by the following
specification without raising a warning:
{{{
sage: IntegerListsLex(5, ceiling=[0,1,2,3,4], length=5)
}}}
--
Ticket URL: <http://trac.sagemath.org/ticket/17979#comment:71>
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