Fig 6. Schematic of the grid used by the class Stencil.

This class retrieves the four nearest neighbors (labeled n, s, e, w) of a central point c. These five points define the pattern known as a five-point stencil. The cells in light blue are the ghost cells required to implement periodic boundary conditions. The prime, double-prime and triple prime indices represent copies of the corresponding indices in the vertical, horizontal and diagonal directions, respectively.