# Math Help - "sign()" notation

1. ## "sign()" notation

Hi,

I'm not sure what subforum to put this in, but here goes...

What does the sign(u) notation mean? For example, in this term taken from the characteristic function of Levy's stable class of distributions:

$c^{\alpha} \left | \lambda \right |^{\alpha} \left(1-i\beta sign(\lambda)\tan{\left(\frac{\alpha\pi}{2}\right) }\right)$

Thanks

2. ## Re: "sign()" notation

Originally Posted by rainer
What does the sign(u) notation mean? For example, in this term taken from the characteristic function of Levy's stable class of distributions:

$c^{\alpha} \left | \lambda \right |^{\alpha} \left(1-i\beta sign(\lambda)\tan{\left(\frac{\alpha\pi}{2}\right) }\right)$
I am sorry to tell you that there may no definitive answer to this question. In the computer algebra system that I use the meaning is:
$sign(x) = \left\{ \begin{gathered} ~0, \hfill\text{ }x=0 \\ ~1, \hfill\text{ }x>0 \\- 1, \hfill\text{ }x<0 \\ \end{gathered} \right.$