The nonlinear Schrödinger limit and the initial layer of the Zakharov equations

We discuss the formation of the convergence of solutions for the Zakharov equations as the ion sound speed λ goes to infinity. We describe how the solutions tend to the corresponding solutions for the nonlinear Schrödinger equation and how the initial layer phenomena occur. A clear account is given of the relation between the convergence rate in λ and the formation of the initial layers.