# Signum

The signum function $\mathrm{sgn} \colon \mathbb{R} \rightarrow \{-1,0,1\}$ (also called the sign function) is the function $$\mathrm{sgn}(x)=\left\{ \begin{array}{ll} 1, & x > 0 \\ 0, & x = 0 \\ -1, & x < 0 \end{array} \right.$$