What Happens When You Identify Points on a Torus and a Rolled Cylinder?

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Discussion Overview

The discussion revolves around the identification of points on a torus and a rolled cylinder, specifically examining the implications of different identification rules on the resulting geometric spaces. Participants explore the nature of these spaces and their dimensional characteristics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the nature of the space resulting from the identification (x,y) ~ (x+2piR, y+2piR) and how it differs from the identification (x,y) ~ (x+2piR, y) and (x,y) ~ (x, y+2piR), which is described as a two-dimensional torus.
  • Another participant suggests that the resulting space is a cylinder rolled up along the diagonal.
  • A participant seeks clarification on what is meant by "the diagonal" in this context.
  • One participant indicates that the diagonal refers to a specific direction in the coordinate system, although this is not visually supported by an attachment that was intended to be shared.
  • There is a discussion about moving along the diagonal by taking (x,y) to (x+a,y+a) and identifying after a = 2Pi, leading to a cylinder rolled along that diagonal.
  • A participant introduces a transformation to new coordinates x' and y' and questions how this affects the identification and the resulting geometry.
  • Another participant notes that for the identification to yield a cylinder, the parameter R must be the same for both x and y coordinates.
  • There is a suggestion that switching to light-cone coordinates results in a cylinder rolled around a different axis.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the resulting space from the various identifications, indicating that multiple competing interpretations exist without a clear consensus.

Contextual Notes

The discussion includes assumptions about the parameters involved in the identifications and the implications of coordinate transformations, which remain unresolved.

ehrenfest
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What is the space resulting from the identification (x,y) ~ (x+2piR, y+2piR)? How is it different from the space resulting from
(x,y) ~ (x+2piR, y)
(x,y) ~ (x, y+2piR), which is a two-dimensional torus (a donut)
 
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It's a cylinder, rolled up along the diagonal.
 
What diagonal?
 
I'd say the diagonal indicated on the attachment (up to symmetry :-p)
 

Attachments

  • diagonal.jpg
    diagonal.jpg
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Last edited:
Sorry, I don't see any attachment. Was that just a joke?
 
No, I forgot to click upload. Apparently you posted while I added it.

(BTW: Post 13^2 for me)
 
13^2

Why would you ask me to post that?
 
He meant he hit post #169, he did not want you to post anything.
 
Take (x,y) to (x+a,y+a) and you move up parallel to the diagonal between the x and the y axis. if you identify after a = 2Pi then you get a cylinder rolled along that diagonal.
 
  • #10
ehrenfest, what happens if you switch to coordinates x' = (x + y)/sqrt(2) and y' = (x - y)/sqrt(2)?
 
  • #11
I see why it is different than the other identification! The R has to be the same for both x and y.

If you switch to light-cone coordinates, then it is a cylinder rolled around the y' axis, right?
 

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