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.

1 Answer

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.