#17053: Add function for disjoint union and ordinal sum of posets
-------------------------------------+-------------------------------------
Reporter: jmantysalo | Owner:
Type: enhancement | Status: needs_work
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):
> But then one cannot say `.disjoint_union(G, 'integers')`. Maybe I don't
worry that much.
I think you worry too much, but if you just need to be soothed then I
would say that it is better this way: some people may be expected to
already use `.disjoint_union(G,True)` while nobody is using
`.disjoint_union(G,'pairs')` are you are creating the syntax.
> As for another post: After `x=42` for example `isinstance(x,
LatticePosets)` says `False`, but `isinstance(x, LatticePoset)` gives
error message.
That's because the combinat guys cannot be trusted to implement anything
reliably.
The error message tells you that `LatticePoset` is not a class, and indeed
it is a function. `LatticePoset??` tells you that it returns
`FiniteLatticePoset` objects, and if you want to know where to find this
class, it is defined there:
{{{
sage: import_statements("FiniteLatticePoset")
from sage.combinat.posets.lattices import FiniteLatticePoset
}}}
then:
{{{
sage: from sage.combinat.posets.lattices import FiniteLatticePoset
sage: x=42
sage: isinstance(x,FiniteLatticePoset)
False
}}}
Nathann
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Ticket URL: <http://trac.sagemath.org/ticket/17053#comment:24>
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