  The general solution to the nonlinear Poisson-Boltzmann equation for two
parallel charged plates, either inside a symmetric elecrolyte, or inside a
2q:-q asymmetric electrolyte, is found in terms of Weierstrass elliptic
functions. From this we derive some exact asymptotic results for the
interaction between charged plates, as well as the exact form of the
renormalized surface charge density.
