Is the Boundary Chart for a Closed Unit Ball Injective?

In summary, the conversation discusses a proof of a closed unit ball being a manifold with boundary. The speaker is struggling with showing that the boundary chart is injective and suggests using a different approach based on the location of the boundary point. They recommend defining a projection map to overcome the obstacle.
  • #1
JYM
14
0
I want to show that a closed unit ball is manifold with boundary and I attempted as uploaded. But I am not happy with the way I showed the boundary chart is injective. Am I right?
 

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  • #2
At the bottom of p1, the assumption that ##U^+## lies in the closed upper half-ball will not hold if the point ##p## has zero ##i##th coordinate.

It looks like you are defining a global map ##\phi## and trying to show its restriction to a nbd of a boundary point on the hypersphere is a homeomorphism to a half-ball. I don't think that will work because of equator points wrt the ##i##th dimension. Instead, choose the putative homeomorphism based on the location of the boundary point. A boundary point must have at least one nonzero coordinate. Say the first nonzero coord of the point is the ##i##th coordinate, then define ##\pi_i## to be the projection map that removes the ##i##th coord.

That should enable you to get around the obstacle.
 
  • #3
I see it. Thanks!
 

What is a manifold with a boundary?

A manifold with a boundary is a mathematical object that is locally similar to Euclidean space, but may have a boundary. It is a type of topological space that is smooth and can be represented by a finite number of coordinate systems.

What is the difference between a manifold and a manifold with a boundary?

The main difference between a manifold and a manifold with a boundary is the presence of a boundary. A manifold has no boundary, while a manifold with a boundary has at least one boundary component. Additionally, the behavior of a manifold with a boundary near the boundary is different from its behavior in the interior.

How is a manifold with a boundary represented?

A manifold with a boundary is typically represented using a coordinate system, where each point on the manifold is assigned a set of coordinates. These coordinates are used to define the shape and properties of the manifold, including its boundary.

What are some examples of manifolds with a boundary?

Some common examples of manifolds with a boundary include a sphere with a boundary (also known as a ball), a cylinder, and a cone. In each of these examples, the boundary is a lower-dimensional object (a point, circle, and line, respectively) that separates the interior from the exterior of the manifold.

What are manifolds with a boundary used for?

Manifolds with a boundary are used in various areas of mathematics and physics, particularly in differential geometry and topology. They are also used in computer graphics and computer vision to represent and analyze shapes and structures in a more efficient and accurate way.

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