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.<p>[0]: <a href="http:&#x2F;&#x2F;www.mit.edu&#x2F;~9.520&#x2F;spring11&#x2F;slides&#x2F;class20_misha.pdf" rel="nofollow">http:&#x2F;&#x2F;www.mit.edu&#x2F;~9.520&#x2F;spring11&#x2F;slides&#x2F;class20_misha.pdf</a><p>[1]: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Coiflet" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Coiflet</a><p>[2]: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Diffusion_map" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Diffusion_map</a>