If you are trying to hack the source, maybe this is not the correct article to read. The purpose of this tutorial is not to delve into the internals of the program. You are not required to know hardly anything about how it is written. Basically, pdnMesh performs a Constrained Delaunay Triangulation of the given region to generate a triangular mesh. It then assimilates a set of equations to be solved according to the mesh of the potentials of each node in the mesh. After solution of the equations, it performs post-processing to enable the user to easily visualise the solution.