#17053: Add function for disjoint union and ordinal sum of posets
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Reporter: jmantysalo | Owner:
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-wishlist
Component: combinatorics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/jmantysalo/add_function_for_direct_sum_of_posets|
7a801e8d3045ef87d8a35d8491ed2e76b18d30a3
Dependencies: | Stopgaps:
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Comment (by ncohen):
> Works. But how to check if class of P is meet- or join-semilattice
without ugly code like this?
I am not sure that you can. The way you do it is wrong, however, for when
you do `type(other) == type(MeetSemilattice({}))` you create a semilattice
object for nothing. What you need is the 'isinstance' Python function.
Then you will probably have to do something like that:
{{{
if isinstance(self, LatticePoset) and isinstance(other, LatticePoset):
return a_lattice
elif isinstance(self, MeetSemilattice) and isinstance(other,
MeetSemilattice):
return a_join_semilattice
elif isinstance(self, JoinSemilattice) and isinstance(other,
JoinSemilattice):
return a_join_semilattice
else:
return a_poset
}}}
The 'if' will execute a bit more code than in your layout, but considering
the operations involved here we do not care at all, the speed loss is
nonexistent. And it is *much* clearer to read.
Nathann
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Ticket URL: <http://trac.sagemath.org/ticket/17053#comment:21>
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