Opened 2 years ago

Last modified 16 months ago

#30080 new enhancement

Manifolds with boundary

Reported by: Matthias Köppe Owned by:
Priority: major Milestone: sage-wishlist
Component: geometry Keywords:
Cc: Eric Gourgoulhon, Dima Pasechnik, Yuan Zhou, Michael Jung Merged in:
Authors: Reviewers:
Report Upstream: N/A Work issues:
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Description (last modified by Matthias Köppe)

(from #30061)

We propose to add manifolds with boundary to sage.manifolds.

Simple examples of topological manifolds with boundary include convex polyhedra and semialgebraic sets with non-singular boundary. These are (except in special cases) not differentiable manifolds, but only "piecewise differentiable" ("manifolds with corners").

References:

Change History (12)

comment:1 Changed 2 years ago by Matthias Köppe

Cc: Dima Pasechnik Yuan Zhou added
Description: modified (diff)

comment:2 Changed 20 months ago by Matthias Köppe

Cc: Michael Jung added

comment:3 Changed 19 months ago by Michael Jung

Perhaps it is better to implement manifolds with corners right away since manifolds with boundaries are just a special case.

https://ncatlab.org/nlab/show/manifold+with+boundary

comment:4 Changed 19 months ago by Matthias Köppe

https://arxiv.org/pdf/0910.3518.pdf (Remark 2.11) has a nice overview over several inequivalent definitions of manifolds with corners.

I haven't checked the details yet but I would be interested in a definition that generalizes all polyhedra, including those with degenerate vertices such as the top of the square pyramid in R3. The main definition in this paper, 2.1(iii), does not fit the bill; it would only include simple polyhedra.

A newer article by the same author: https://www.sciencedirect.com/science/article/pii/S0001870816307186 on manifolds with "generalized corners" ("g-corners")

Last edited 19 months ago by Matthias Köppe (previous) (diff)

comment:5 Changed 19 months ago by Dima Pasechnik

hmm, what is "the top of the square pyramid in R3" ?

Do you mean to say that you'd like a definition that includes all the non-simple polytopes, at least?

(vertices of non-convex polyhedra are a different story, much more complicated)

comment:6 in reply to:  5 Changed 19 months ago by Matthias Köppe

Replying to dimpase:

Do you mean to say that you'd like a definition that includes all the non-simple polytopes, at least?

Yes

comment:7 in reply to:  5 Changed 19 months ago by Matthias Köppe

Replying to dimpase:

(vertices of non-convex polyhedra are a different story, much more complicated)

More complicated than modeling them locally by a polyhedral fan?

comment:8 Changed 19 months ago by Dima Pasechnik

should one call a vertex the point in the middle of the twised prism one gets from enough twisting? If you do, you get a vertex in the middle of an edge. If you don't, you get facets without an orientation...

comment:9 Changed 18 months ago by Matthias Köppe

Description: modified (diff)

comment:10 Changed 16 months ago by Matthias Köppe

Description: modified (diff)

comment:11 Changed 16 months ago by Michael Jung

I think a first reasonable step would be to introduce "boundary charts".

Tbh, I don't know how sensible it is to start with the most general concept of "boundary-like". Manifolds with corners seem fairly doable. The generalization by Joyce looks very interesting, though I reckon it's pretty hard to implement.

comment:12 in reply to:  11 Changed 16 months ago by Matthias Köppe

Replying to gh-mjungmath:

I think a first reasonable step would be to introduce "boundary charts".

Well, #31894 is a step into this direction

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