2-d acoustics with variable coefficients.

Two materials with a single interface, specified in fdisc.f (which is called
from cellave.f to compute the fraction of each grid cell lying in the left
and right states).

The sound speed and impedance are stored in the aux array.
For cells cut by the interface, the arithmetic average of rho and harmonic
average of the bulk modulus are used to determine these parameters for this
cell.



WARNING: This example was modified February, 2006 to use
Version 4.3 of clawpack and the associated matlab scripts.