Geometric mean

Given $k$ values $w_i \in \mathbb{R}$ for $1 \leq i \leq k$ we define the geometric mean to be

$$\left( \prod_{i=1}^k w_i \right)^{1/k}.$$

This might end up being in the complex numbers if $k$ is even, so some people make the restriction that $w_i \geq 0$.