Analytical solution for an acoustic wave emitted by a Gaussian pulse as
described in Tam: Computational Acoustics, a wave number approach.
Appendix G.3.

The pulse is described geometrical by an origin and a halfwidth, where
center is the location of the maximum in the spherical Gaussian pulse, and
halwidth is the radius at which the pulse has half the value of the
maximum.
The height of the pulse is given by amplitude.
Note, this definition matches the gausspulse spatial function, which can be
used as an initial condition to this problem.
Additionally the speed of sound and the background pressure are required
to compute the solution.

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