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The classical porous media equation is

$$u_t - \Delta(u^m) = 0 \quad m>1.$$

Has the (degenerate) wave equation $$u_{tt} - \Delta(u^m) = 0$$ been subject of studies? What would the physical interpretation of such a wave equation be?

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  • $\begingroup$ How to interpret the equation for negative $u$? Or should $m$ be a odd integer? $\endgroup$ Commented Apr 23, 2019 at 3:18
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    $\begingroup$ for $m=2$ and a minus sign in front of the Laplacian this is the zero-water-depth limit of the Boussinesq shallow-water wave equation $\endgroup$ Commented Apr 23, 2019 at 10:44
  • $\begingroup$ @CarloBeenakker Thank you. Do you have a reference where such zero-water-depth limit is studied? $\endgroup$
    – Riku
    Commented Apr 23, 2019 at 10:53

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