Amplitude of the damping term

[jiwei08]

I'm trying to solve the wave equation in $\mathbb{R}^2$ and use the abc methods which add a damping term to the original equation. The amplitude of the damping term is related to the maximum of the velocity $v_{max}$, namely a scaling factor $1/v_{max}$, as shown in the notebook. But the function initialize_damp() in examples/seismic/model.py seems to omit it, which would lead to the wrong solution for the case that $c$ is much larger or smaller than $1$.

Any feedback would be appreciated.