Ugh, that sounds terrible. During a previous internship at a HPC company[0] I implemented a computational electrodynamics FDTD algorithm as given in the Taflove book[1], and I made more than enough errors even without the book containing mistakes! Two fields, each with three components and subtly different equations for all. What a nightmare. Especially since it's impossible to tell what is wrong when watching the EM wave propagate in an impossible oblong fashion during your simulation.

[0] http://www.acceleware.com/

[1] http://www.amazon.ca/Computational-Electrodynamics-Finite-Di...