Hydrodynamical limit for a nongradient system: The generalized symmetric exclusion process

We consider a symmetric simple exclusion process where at most two particles per site are permitted. This model turns out to be nongradient. We prove that the particles' densities, under a diffusive rescaling of space and time, converge to the solution of a diffusion equation. We give a variational characterization of the diffusion coefficent. We also prove, for the generator of the process in finite volume, a lower bound on the spectral gap uniform in the volume. © 1994 John Wiley & Sons, Inc.