Periodic Boundary Conditions

Periodic boundaries map to each other; material passing through a periodic boundary will emerge from the face of the opposing periodic boundary with the same velocity (think Pac-Man).

Domains in AstroBEAR can have anywhere from 0 to 2n periodic boundaries, where n is the number of dimensions in the problem. These boundaries always occur in pairs, with opposite faces of the domain being periodic with each other.

Periodic boundaries are often used to model large-scale systems. In a bulk-volume problem with no well-defined surfaces (such as the interior of a large diffuse molecular cloud), periodic boundaries can be used to simulate the effect of similar adjacent domains. Essentially, it assumes that neighboring regions are of a sufficiently similar character that a tiled representation of the cloud is a viable one.