Determination of denominator functions for a NSFD scheme for the Fisher PDE with linear advection

We examine and discuss the general problem of how “denominator functions” are to be calculated when using nonstandard finite difference (NSFD) methods for constructing discrete models of differential equations. Using the example of the Fisher PDE with linear advection, we show that the denominator functions follow from a simple algorithm. An important class of equations for which this method can be applied are those evolution PDE’s describing nonlinear wave phenomena.