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:

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

Thanks