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First of all I have to say that I am not very competent in topology, so please try not to use too obscure terms in your answers and pardon me for my explanations that may not be very rigorous.

I am using a 3-manifold that is almost (you'll see why I say almost in a few lines) a 3-sphere defined on $(\psi, \theta, \phi)$ that are respectively defined on $[0 ; \pi/2], [0 ; \pi/2], [0 ; 2\pi]$. So it is a some sort of a quarter 3-sphere.

But this manifold has an important property: for every possible set of coordinates $(\psi, \theta, \phi)$, the value at this position will be equal to the one at the position $(\theta, \psi, \phi)$. In other words there is a symmetry between the coordinates $\psi$ and $\theta$.

I am struggling to figure out what is the consequence of this on the shape of the 3-manifold, but this is more by curiosity. The real question is: since there is a symmetry, we have redundancy of information. Is there a possibility to parametrize the manifold to a new set of coordinates (or to find an equivalent manifold) to simplify it and avoid redundancy?

Any help, or any advice, would be appreciated.


EDIT : Here is a first attempt.

If this symmetry property is true, we can propose the following parameterization $(u,v,w)$, with $u \in [0, \pi/2]$, $v \in [0, u]$ and $w \in [0, 2\pi]$, with :

$$\begin{cases}u = \psi \text{ if } \theta < \psi \text{ else } \theta\\ v = \theta \ \text{ if } \theta < \psi \text{ else } \psi\\ w = \phi\end{cases}$$

This will avoid redundancy. But what will be the consequences of this?

Balfar
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  • One idea would be to study whatever you want to study, on half of the manifold, so as to suppress the redundancy. With perhaps some limit conditions on the cut so as to ensure whatever regularity (e.g. differentiability) you need. It seems you are doing something similar with $(u,v,w)$, but the domain is double (instead of half) to that of $(\psi, \theta, \phi)$, so I don't get your idea. Could you express $(u,v,w)$ in terms of $(\psi, \theta, \phi)$? – Jean-Armand Moroni Aug 31 '23 at 13:08
  • This not possble to give a meningful answer without knowing how the coordinates map to the 3-sphere. For example, with appropriate mapping, one can get all of the 3-sphere. – emacs drives me nuts Sep 01 '23 at 09:39

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