#18223: cartesian products with orders
-------------------------------------+-------------------------------------
Reporter: dkrenn | Owner:
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-6.7
Component: categories | Resolution:
Keywords: sd67 | Merged in:
Authors: Daniel Krenn | Reviewers: Benjamin Hackl
Report Upstream: N/A | Work issues:
Branch: u/behackl/cat | Commit:
/cartesian-product-posets | 0690e716b925505dc34b77338af0da8f35fc53a4
Dependencies: #18586 | Stopgaps:
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Changes (by vdelecroix):
* status: needs_info => needs_work
Comment:
Hello,
1. I think that the class `CartesianProductPosets` would better be
somewhere in `combinat/posets` rather in `sets/cartesian_product`. It is
always better to split files.
2. Why is the following not a poset
{{{
sage: P = Poset((srange(3), lambda left, right: left <= right))
sage: cartesian_product([P,P]).category()
Category of Cartesian products of finite enumerated sets
}}}
3. The argument `order` in the class `CartesianProductPosets` is
mandatory. While the following just works
{{{
sage: C = cartesian_product([ZZ, ZZ], extra_category=Posets())
}}}
actually not
{{{
sage: TestSuite(C).run()
Failure in _test_not_implemented_methods:
Traceback (most recent call last):
...
AssertionError: Not implemented method: le
------------------------------------------------------------
The following tests failed: _test_not_implemented_methods
}}}
4. As I already said, it would make sense to have the product order as a
default since it is '''the''' cartesian product (in a categorical sense
when morphisms are increasing functions).
Vincent
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Ticket URL: <http://trac.sagemath.org/ticket/18223#comment:18>
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