The Modulus function

[Aeneas]

Is "The modulus function" one function or two? f(x) = |x| suggests one, but f(x)=x, x>=0, f(x)=-x, x<0, suggests two.

[neutrino]

The modulus function is one function. It is an example of what is known as a piecewise function (http://mathworld.wolfram.com/PiecewiseFunction.html).

[bel]

It's one function. Many other functions are written like this, where one function is defined by one function on one interval and defined by another function on another interval, they're called piece-wise functions.

[Aeneas]

Many thanks neutrino and bel.