## 2016-11-17 Finding extremal values in a nd-array

Sometimes, you need to pick up the $N$-th extremal values in a mutli-dimensional matrix.

Let's suppose it is represented as a `nd-array`

(here, I further suppose you are using the numpy library from the python language). Finding extremal values is easy with `argsort`

but this function operated on 1d vectors... Juggling around indices is sometimes not such an easy task, but luckily, we have the `unravel_index`

function.

Let's unwrap an easy solution combining these functions: