## Archive of posts in Jan, 2023

• ### This is what will happen after you get a haircut

Denote the length distribution of one’s hair to be $f(l,t)$, where $l$ is hair length, and $t$ is time. Considering that each hair may be lost naturally from time to time (there is a probability of $\lambda\,\mathrm dt$ for each hair to be lost within time range from $t$ to $t+\mathrm dt$) and then restart growing from zero length, how will the length distribution of hair evolve with time? It turns out that we may model it with a first-order PDE.

• ### I want to invent a better way to read numbers

Reading numbers in English is a pain. I want to invent a better way to read numbers!