I'm struggling to find a function [itex]E(t)[/itex] which is the energy inside a sphere with energy density [itex]\rho(t,r)[/itex] where the radius [itex]r \equiv r(t)[/itex] is itself a function of time. This(adsbygoogle = window.adsbygoogle || []).push({});

[tex]

E(t) = 8\pi \int_0^{r(t)} \rho(r,t) dr

[/tex]

doesn't make sense, does it ? Is the thing I'm looking for some kind of convolution of r and [itex]\rho[/itex] ?

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# Is this integral a convolution ?

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