Differentiating Fluid
By differentiating a fluid simulator, one can solve via gradient decent for the initial velocity field that brings a fluid from one configuration to another.
Gallery
A fluid moving from the chinese characters feng to shui.
Metadata
This 200x200 mini animation took 1hr to solve. It's a legit fluid simulator, and it solves for the velocity field that brings the first image to the next.
This was done with the amazing DiffTaichi, with one of the examples given by the authors.
The chinese words are 风水, meaning (from my understanding) fortune vibes, for lack of better terms.
Code
I have determined the code to be too messy to be worth cleaning up and post.