- #1
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Hi.
I'm considering the covariant derivative
[tex]\nabla_\mu V^\nu = \partial_\mu V^\nu + \Gamma_{\mu\nu}^\lambda V^\lambda[/tex]
in spherical coordinates in flat 3D space (x = r cos sin, y = r sin sin, z = r cos; usual stuff).
Now I wrote down the gradient of a scalar function f, for which I got [itex]\nabla_\mu f = \partial_\mu f[/itex] (having constructed the derivative to reduce to the ordinary partial derivative on scalars) which is of course not correct, it should be something like
[itex] \partial_r f, \frac{1}{r} \partial_\theta f \text{ and } \frac{1}{r \sin\theta} \partial_\phi f[/itex] for the three components.
Same when I try to derive an expression for the divergence of a vector field, and then I need to show that it is the same as the familiar
[tex]\frac{1}{r^2} \frac{\partial}{\partial r} (r^2 V^1) + \frac{1}{r \sin\theta} \frac{\partial}{\partial\theta} (\sin\theta V^2) + \frac{1}{r \sin\theta} \frac{\partial V^3}{\partial \phi}[/tex]
Of course,
[tex]\nabla_\mu V^\nu = \partial_\mu V^\mu + \Gamma_{\mu\mu}^\nu V^\nu[/tex]
(that must be correct) but if plug in the connection coefficients I calculated, I get an otherwise correct result, except there are some factors 1/r and 1/r sin theta missing.
I have a feeling I'm mixing up my coordinate systems here, but how?
I did get the right result for the Laplacian [itex]\nabla^2 f[/itex] by the way ... isn't that odd?
I'm considering the covariant derivative
[tex]\nabla_\mu V^\nu = \partial_\mu V^\nu + \Gamma_{\mu\nu}^\lambda V^\lambda[/tex]
in spherical coordinates in flat 3D space (x = r cos sin, y = r sin sin, z = r cos; usual stuff).
Now I wrote down the gradient of a scalar function f, for which I got [itex]\nabla_\mu f = \partial_\mu f[/itex] (having constructed the derivative to reduce to the ordinary partial derivative on scalars) which is of course not correct, it should be something like
[itex] \partial_r f, \frac{1}{r} \partial_\theta f \text{ and } \frac{1}{r \sin\theta} \partial_\phi f[/itex] for the three components.
Same when I try to derive an expression for the divergence of a vector field, and then I need to show that it is the same as the familiar
[tex]\frac{1}{r^2} \frac{\partial}{\partial r} (r^2 V^1) + \frac{1}{r \sin\theta} \frac{\partial}{\partial\theta} (\sin\theta V^2) + \frac{1}{r \sin\theta} \frac{\partial V^3}{\partial \phi}[/tex]
Of course,
[tex]\nabla_\mu V^\nu = \partial_\mu V^\mu + \Gamma_{\mu\mu}^\nu V^\nu[/tex]
(that must be correct) but if plug in the connection coefficients I calculated, I get an otherwise correct result, except there are some factors 1/r and 1/r sin theta missing.
I have a feeling I'm mixing up my coordinate systems here, but how?
I did get the right result for the Laplacian [itex]\nabla^2 f[/itex] by the way ... isn't that odd?