# Subscript plus and negative sign

What is the precise mathematical definition of the positive and negative subscript signs as in the following function?

$f(\mu) = \displaystyle\sum_{i=1}^n \alpha (x_i - \mu)_{+} + (1- \alpha)(x_i - \mu)_{-}$

• Possibly: $z_+=\max (z,0)$ and $z_ -=\min (z,0)$. Does that make sense in your context? – lulu Apr 13 '16 at 13:49
• Do you have a reference to the source of this function? Typically any text with mathematics should have a notation section that should have what you are looking for. In my experience there are different notations for mathematicians, physicists, computer scientists, engineers and more! – JStrahl Jan 25 '17 at 8:20
• Similar question with further discussion math.stackexchange.com/questions/215211/… – JStrahl Jan 25 '17 at 8:23