Finding position vector in general local basis

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    General Position Vector
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SUMMARY

The position vector in a general local basis, such as spherical coordinates, is defined as ##\vec r = r \hat {\mathbf e_r}##, where ##r## represents the distance from the origin and ##\hat {\mathbf e_r}(\theta,\phi)## is the unit vector pointing in that direction. This derivation is rooted in the definition of the coordinate system, emphasizing that the local basis vectors are specific to the coordinate system being used. In contrast, a global Cartesian basis allows for expressing Cartesian coordinates and basis vectors in terms of curvilinear coordinates.

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farfromdaijoubu
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How do you derive the position vector in a general local basis?

For example, in spherical coordinates, it's ##\vec r =r \hat {\mathbf e_r}##, not an expression that involves that involves the vectors ## {\hat {\mathbf e_{\theta}}}## and ## \hat {{\mathbf e_{\phi}}}##. But how would you show this?
 
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This follows from the definition of the coordinate system. For example, in spherical polar coordinates, r is by definition the distance of a point from the origin and \mathbf{e}_r(\theta,\phi) is the unit vector in the direction of that point. Hence \mathbf{r} = r\mathbf{e}_r(\theta,\phi).

Otherwise, if you have a global Cartesian basis then you can express the cartesian coordinates and basis vectors in terms of the curvilinear coordinates and basis vectors.
 
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