Specify initial conditions for the wave equation

[pausz]

The discretized approximation of the continuum damped wave equation is a Initial Value Boundary Problem. As such, it requires specification of the initial conditions for the internal grid points and the points at the boundaries. The latter condition is relevant for boundaries other than Periodic Boundary Conditions (eg, absorbing boundary conditions).

Furthermore, user defined initial conditions for phi and dphi are essential to validate the code with exact solutions of the wave equation. The current version of wave.cpp sets spatially uniform initial conditions, so it is not possible to set phi(x,y,0) = I(x,y), where I(x,y) is a spatial profile for which we know the exact solution phi(x,y,t) without a source term (eg, without a stimulus). This case could be solved if we had the restarting mechanism (#24).