What do you call $-f(x)$ I have a terminology question. I am referring to a sigmoid (S-shape function) in a paper however it is inverted (if the sigmoid is $f(x)$, my function $-f(x)$).
I initially wanted to refer to it as an inverse sigmoid... but I think that would refer to $f^{-1}(x)$ ?
Any help welcome! thank you 
 A: I suppose that negated is the right name:
$f(x)$ negated is $-f(x)$
A: If you multiplied by $-1$ then the symbol is $-f(x)$.
If you found the inverse function (then the composition is the identity) then the symbol is $f^{-1}(x)$
A: I agree with graziano governatori that "negated sigmoid" is a good name. 
Another possibility is "reflected sigmoid". 
But as Matt Pressland wrote, whatever terminology you chose in the end you should clearly define it. 
A: It depends on what you want to stress. If you only mean a left-right flipped S shape, I think it is usually called a "negative sigmoid" (example 1 on p.4, example 2, example 3 on p.4). However, logistic-like functions with negative parameters such as $1/(1+e^{-(-x)})$ are also called negative sigmoids. Certainly, such functions can be written in the form of
$$\mathtt{constant} + \mathtt{negative\ multiple} * \mathtt{some\ sigmoid}(x),$$
but the stress here is the shape of the curve rather the negative multiple itself.
If you want to stress that the function is constructed by multiplying a sigmoid function by a negative number, I don't know the proper name, but I agree with the others here that "negated sigmoid" is a good name. Yet, a google search on "negated sigmoid" returns only 25 results. So this is perhaps not a very common name.
