Are there any other ways of parametizing S?

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Discussion Overview

The discussion revolves around the parametrization of a surface S defined as part of the plane z = y - 2, which lies inside the elliptic cylinder x² + 4y² = 4. Participants explore various methods of parametrizing S and inquire about alternative approaches.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes a parametrization using x = 2sin(t), y = cos(t), z = cos(t) - 2, and seeks confirmation on its correctness.
  • Another participant suggests that the sine and cosine terms may be switched and questions the direction of the parameterization, assuming a counter-clockwise direction.
  • A later reply indicates that there is no specific starting point for the parametrization and asks for alternative methods.
  • One participant suggests that switching sine and cosine could be a valid alternative, mentioning the possibility of adding an arbitrary phase shift to the trigonometric functions.
  • Another participant expresses confusion regarding the parametrization of a surface, emphasizing the need for two parameters and proposing a different parametrization involving a radius R.
  • It is noted that switching sine and cosine will yield a different starting point and direction but will trace the same curve.
  • One participant mentions that the parameters discussed would draw the curve of intersection and refers to Klein's equation for parametrizing the entire surface.

Areas of Agreement / Disagreement

Participants express differing views on the correctness of the initial parametrization and the necessity of two parameters for surface parametrization. There is no consensus on a single alternative method, and multiple competing views remain regarding the appropriate approach.

Contextual Notes

Some participants highlight the need for clarity on the definitions and assumptions regarding the parametrization of surfaces versus curves, as well as the implications of phase shifts and parameter direction.

Sneaksuit
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If S is part of the plane [tex]z = y - 2[/tex] that lies inside the elliptic cylinder [tex]x^2 + 4y^2 = 4[/tex] and I want to parametrize S I will let
[tex]x = 2sin(t)[/tex]
[tex]y = cos(t)[/tex]
[tex]z = cos(t) - 2[/tex]
I assume this is right but let me know if not. My question is are there any other ways of parametizing S?
 
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I think you ahve your cosins and sins switched. Which direction does your parameter go? I am assuming counter clockwise.

Come to think of it keeping them that way will also work, provided that you aren't going for a specific parametric starting and ending point.
 
There is no specific starting point. Do you know of another way parametrizing S though?
 
Sneaksuit said:
There is no specific starting point. Do you know of another way parametrizing S though?

Basically as he said, make every cosine a sine and the sine a cosine. I suppose you could also add an arbitrary phase shift to the trig functions as well (the sine-cosine reversal is a special case of that).
 
So just switch my sin and cosin and that is another way of parametrizing S?
 
I don't really understand your solution, since apparently you're parametrizing a surface (so you need 2 parameters). I suppose the solution is simply :

[tex]x=Rcos(t)\quad y=\frac{R}{2}sin(t)\quad z=\frac{R}{2}sin(t)-2\quad R\in[0;2]\quad t\in[0;2\pi][/tex]
 
Sneaksuit said:
So just switch my sin and cosin and that is another way of parametrizing S?

Yes. It will draw the same curve but from a different starting point and direction.
 
Those parameters would draw the curve of intersection. Parametrizing the entire surface, you would use klein's equation
 

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