#18529: Topological manifolds: basics
-------------------------------------+-------------------------------------
Reporter: egourgoulhon | Owner: egourgoulhon
Type: enhancement | Status: needs_info
Priority: major | Milestone: sage-6.10
Component: geometry | Resolution:
Keywords: topological | Merged in:
manifolds | Reviewers: Travis Scrimshaw
Authors: Eric Gourgoulhon, | Work issues:
Travis Scrimshaw | Commit:
Report Upstream: N/A | 0fb39df7fafe7f0a765bf73b3f34a6cb41e65c40
Branch: | Stopgaps:
u/tscrim/top_manifolds_refactor |
Dependencies: #18175 |
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Comment (by egourgoulhon):
Replying to [comment:61 egourgoulhon]:
>
> No, not at the moment: I've worked on the subsequent tickets to check if
the introduced changes (in particular the removal of unique
representation) propagate smoothly. So far, so good...
>
Bad news: the removal of unique representation breaks parallel
computations in #19147 (affine connections). For instance, in the branch
of #19147, if one performs
{{{
sage: M = Manifold(3, 'M')
sage: X.<x,y,z> = M.chart()
sage: nab = M.affine_connection('nabla', r'\nabla')
sage: nab[0,0,1], nab[2,1,2] = x^2, y*z
sage: use_multiproc(2) # parallelization on 2 proc
sage: nab.riemann()
}}}
one gets the error message:
{{{
RuntimeError: There is a bug in the coercion code in Sage.
Both x (=Scalar field on the 3-dimensional differentiable manifold M) and
y (=Scalar field on the 3-dimensional differentiable manifold M) are
supposed to have identical parents but they don't.
In fact, x has parent 'Algebra of differentiable scalar fields on the
3-dimensional differentiable manifold M'
whereas y has parent 'Algebra of differentiable scalar fields on the
3-dimensional differentiable manifold M'
}}}
and sage terminates badly (core dumped).
The reason is that the parallelization is using the pickling: the parallel
iterator `sage.parallel.multiprocessing_sage.parallel_iter` invokes the
function `sage.misc.fpickle.pickle_function`.
With unique representation, the pickling was fine and the above issue did
not occur.
Note that parallelization of heavy computations like that of the Riemann
tensor is really important!...
--
Ticket URL: <http://trac.sagemath.org/ticket/18529#comment:74>
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