wave.py example does not compute a solution

[ZakHodgson]

Hey there, thank you for your work.

running wave.py does not seem to produce a solution.
The loss begins at approximately -0.00012 or so, then continues over iterations to, -1, -2, ... ,-50,
but the img solution is just a blank white square.

After toggling the setup on line 125, the first iteration shows waves propagating, but later ones are back to a blank white square.

Perhaps the values of p are simply clipping?

Particle based examples (diffmpm.py) and water_renderer.py work fine.

Any ideas?