# What does 'sign' mean in an equation?

I'm curious what sign means in the context of mathematical notation. I'm reading a paper right now and it uses:

$$sign \overrightarrow{\lambda} \cdot \overrightarrow{a}$$

Is that equivalent to $\pm$ ?

I've never seen this before.

Thanks.

• probably signum, which is $1$ if the argument is positive, $-1$ if the argument is negative, and $0$ if the argument is exactly $0.$ – Will Jagy Nov 14 '13 at 6:01
• It is used as the $\large{\tt sgn}$ function. – Felix Marin Nov 14 '13 at 6:38

The value $\operatorname{sign}(x)$ equals $-1$, $0$, or $1$ depending upon whether the value $x$ is negative, zero, or positive. Sometimes this is written as $\operatorname{sgn}(x)$ as is the case here.