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A doubly nonlinear evolution for the optimal Poincaré inequality

We study the large time behavior of solutions of the PDE $|v_t|^{p-2}v_t=Δ_p v$. A special property of this equation is that the Rayleigh quotient $\int_Ω|Dv(x,t)|^pdx /\int_Ω|v(x,t)|^pdx$ is nonincreasing in time along solutions. As $t$ tends to infinity, this ratio converges to the optimal constant in Poincaré's inequality. Moreover, appropriately scaled solutions converge to a function for which equality holds in this inequality. An interesting limiting equation also arises when $p$ tends to infinity, which provides a new approach to approximating ground states of the infinity Laplacian.