A formula for the area of a triangle: Useless, but explicitly in Deep Sets form

Connor Hainje, David W. Hogg

Any permutation-invariant function of data points ${\vec{r}}_i$ can be written in the form $\rho ({\sum }_i\varphi ({\vec{r}}_i))$ for suitable functions $\rho$ and $\varphi$. This form - known in the machin…