There are diffusion based methods for unsupervised learning based on the graph laplacian, or heat kernel [0]. Maybe this is what she was referring to? I would g

There are diffusion based methods for unsupervised learning based on the graph laplacian, or heat kernel [0]. Maybe this is what she was referring to? I would guess so, because Coifman (who is also closely tied to wavelets [1]) introduced the diffusion maps [2] method. On the other hand, I have not seen any unsupervised method based on say, Navier-Stokes, which is the only other thing that comes to mind for regarding ink drops diffusing. [0]: http://www.mit.edu/~9.520/spring11/slides/class20_misha.pdf http://www.mit.edu/~9.520/spring11/slides/class20_misha.pdf [1]: https://en.wikipedia.org/wiki/Coiflet https://en.wikipedia.org/wiki/Coiflet [2]: https://en.wikipedia.org/wiki/Diffusion_map https://en.wikipedia.org/wiki/Diffusion_map