Complex sentence: The finite-difference frequency-domain (FDFD) is a numerical solution for problems usually in electromagnetism, based on finite-difference approximations of the derivative operators in the differential equation being solved.
Split into simpler sentences: The finite-difference frequency-domain (FDFD) is a numerical solution for problems usually in electromagnetism. The method is, of course, based on finite-difference approximations of the derivative operators in the differential equation being solved.