In this paper, we extend the reduced-basis approximations developed earlier for linear elliptic and parabolic partial differential equations with affine parameter
dependence to problems involving (a) nonaffine dependence on the
parameter, and (b) nonlinear dependence on the field variable.
The method replaces the nonaffine and nonlinear terms with a coefficient function approximation which then permits an efficient offline-online computational
decomposition. We first review the coefficient function approximation procedure: the essential ingredients are (i) a good collateral
reduced-basis approximation space, and (ii) a stable and inexpensive
interpolation procedure. We then apply this approach to linear nonaffine and nonlinear elliptic and parabolic equations; in each
instance, we discuss the reduced-basis approximation and the associated offline-online computational
procedures. Numerical results are presented to assess our approach.