# Where is the function reference?

#### elim

Anyone knows what's the name of the function $H(x,x_0) = \begin{cases} 1& x\ge x_0,\\ 0& x< x_0.\end{cases}$,
and where is the online reference of it?

Thanks

#### romsek

Math Team
That's usually referred to as the unit step function although it's usually written as

$U(x) = \begin{cases}0&x<0\\1&0 \leq x\end{cases}$

and you get it "turning on" at $x_0$ by using $U(x-x_0)$

Forum Staff