#18529: Topological manifolds: basics
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Reporter: egourgoulhon | Owner: egourgoulhon
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-6.10
Component: geometry | Resolution:
Keywords: topological | Merged in:
manifolds | Reviewers:
Authors: Eric Gourgoulhon | Work issues:
Report Upstream: N/A | Commit:
Branch: | f342e03e7008831c4789b94b03674c1a0cbbf3a6
public/manifolds/top_manif_basics | Stopgaps:
Dependencies: #18175 |
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Comment (by egourgoulhon):
Replying to [comment:38 tscrim]:
> Oh yea...pickling. Uggg...
>
> I worry that the current equality check is too general. Perhaps also for
equality add a check to see if the current atlases are equal (or one is a
subset of the other), which in turn would have to check equality on
charts? Overall it is not pretty, but I would hope one is not checking
equality of manifolds too often
Unfortunately yes: charts are used as dictionary keys for the coordinate
expressions of scalar functions defined on the manifold (these functions
will appear massively as the components of tensor fields), therefore one
checks often equality of charts and the latter starts by checking the
equality of manifolds on which they are defined. By the way, if we
introduce the check of atlases in the manifold equality, there is a danger
of endless loop: to compare charts, one first compare their domains, i.e.
manifolds... To circumvent this, maybe we should introduce two comparison
operators: a fast `__eq__`, which cheks only the name, dimension and base
field and a more mathematically meaningful `is_isomorphic_to`, which
checks in addition the atlases.
--
Ticket URL: <http://trac.sagemath.org/ticket/18529#comment:39>
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