A doubly nonlinear evolution for the optimal Poincar�� inequality

We study the large time behavior of solutions of the PDE $|v_t|^{p-2}v_t=��_p v$. A special property of this equation is that the Rayleigh quotient $\int_��|Dv(x,t)|^pdx /\int_��|v(x,t)|^pdx$ is nonincreasing in time along solutions. As $t$ tends to infinity, this ratio converges to the optimal constant in Poincar��'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.