Adding generic sources to high-order finite-difference schemes

General electromagnetic problems may require specialized incident fields that may not be easily accommodated in the traditional scattered field formulation. In implementing such incident fields in a high-order formulation, care should be taken to insure that the source is implemented in a consistent manner with the numerical scheme. The details of implementing a scattered field / total field interface for compact-difference schemes will be addressed. Additionally, a modified algorithm for implementing sources in the standard Runge-Kutta time integration schemes will be proposed to reduce numerical error.