  A procedure suggested by Vvedensky for obtaining continuum equations as the
coarse-grained limit of discrete models is applied to the restricted
solid-on-solid model with both adsorption and desorption. Using an expansion of
the master equation, discrete Langevin equations are derived; these agree
quantitatively with direct simulation of the model. From these, a continuum
differential equation is derived, and the model is found to exhibit either
Edwards-Wilkinson or Kardar-Parisi-Zhang exponents, as expected from symmetry
arguments. The coefficients of the resulting continuum equation remain
well-defined in the coarse-grained limit.
