Geometric realization of topology

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Discussion Overview

The discussion revolves around the geometric realization of cell complexes, specifically cw-complexes, and how to assign geometric representations to various cells such as vertices, edges, faces, and volumes. Participants explore the relationship between topology and geometry in this context, with a focus on simplicial complexes and their mappings.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that geometric realization can be achieved by mapping coordinates to 0-cells, but express uncertainty about how to extend this to edges, faces, and volumes.
  • Others mention that for simplicial complexes, there exists a simplicial map into the standard simplex in n-dimensions, where n corresponds to the number of vertices.
  • One participant emphasizes the challenge of representing curvilinear meshes within the framework of cell complexes, suggesting that linear complexes may not suffice for such representations.
  • Another participant asserts that a linear complex can be embedded in the standard simplex, indicating a potential misunderstanding of the original question regarding cw-complexes.
  • There is a suggestion that any cw-complex may have a simplicial decomposition, but the existence of a general algorithm for geometric realization remains uncertain.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between cw-complexes and simplicial complexes, with some asserting that they are fundamentally different in terms of topology and geometry. The discussion remains unresolved regarding the specific methods for geometric realization of cw-complexes.

Contextual Notes

Participants note that the definition of cw-complexes is based purely on topology, which complicates the assignment of geometric realizations. There is also mention of an existence theorem without a clear algorithm for practical application.

s_jubeh
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Hello,

Suppose that I have a cell complex and I want to define it's geometric realization, I can do it via mapping such that assign coordinates to 0-cells. however how can i do that for edges, faces and volumes. is there is ageneral formulas for lines, faces and volumes.

Regards
 
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s_jubeh said:
Hello,

Suppose that I have a cell complex and I want to define it's geometric realization, I can do it via mapping such that assign coordinates to 0-cells. however how can i do that for edges, faces and volumes. is there is ageneral formulas for lines, faces and volumes.

Regards

For a simplicial complex there is a simplicial map of the complex into the standard simplex in n-dimensions - where n is the number of vertices in the complex.
 
Dear wofsy,

I did not understand your reply " I am not an expert in this field". Actually my problem lies in representing geometrical objects. Suppose that I have a cell complex (cw-complex) such that each cell in this complex can be a assigned geometrical realization.

fro example

vertix ----> point

edge ----> line (curved )

face ----> surface

...

if I am talking about linear complex, it is enough to assign points to vertexes. however suppose that the mesh that I want to represent is curvilinear mesh. this is not possible.

Regards
 
s_jubeh said:
Dear wofsy,

I did not understand your reply " I am not an expert in this field". Actually my problem lies in representing geometrical objects. Suppose that I have a cell complex (cw-complex) such that each cell in this complex can be a assigned geometrical realization.

fro example

vertix ----> point

edge ----> line (curved )

face ----> surface

...

if I am talking about linear complex, it is enough to assign points to vertexes. however suppose that the mesh that I want to represent is curvilinear mesh. this is not possible.

Regards

Not sure what you are talking about. A linear complex can be embedded in the standard simplex in n dimensions. The algorithm is trivial. But maybe you are trying to do something else.
 
Dear wofsy,

Can you please direct me to this algorithm and some explanation. It seems that we are talking about different things.

Thanks
 
The standard n simplex has n+1 vertices and is a subset of R^n. Any subset of vertexes spans a lower dimensional simplex so any linear simplicial complex with n or less vertices is a subset of this one.
 
Derar Wofsy,

wofsy said:
The standard n simplex has n+1 vertices and is a subset of R^n. Any subset of vertexes spans a lower dimensional simplex so any linear simplicial complex with n or less vertices is a subset of this one.

I think we are talking about diffrent things, I am interested in cw-complex. the defenesion of cw-complex is purly based on topology not geometry. so my question is how to add geometric realization to cw-complexes.

Regards
 
s_jubeh said:
Derar Wofsy,
I think we are talking about diffrent things, I am interested in cw-complex. the defenesion of cw-complex is purly based on topology not geometry. so my question is how to add geometric realization to cw-complexes.

Regards

I didn't mean to give you a complete answer. But a simplicial complex is a cw-complex and it may be that any cw-complex has a simplicial decomposition. I gave you a geometric realization of an arbitrary simplicial complex whether defined topologically or combinatorally.

in general I am not sure - at best you can have an existence theorem
 

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