What's the term for the number of outputs a function has?

Question

That is, if a function's arity is the number of inputs it has, its __ is the number of outputs it has. (Fill in the blank.)

Answer 1

I am pretty sure, based on a Google search, that at least some people call this notion "coarity" (or "co-arity" if you want the pronunciation to be clearer).

Answer 2

The question doesn’t arise: by definition a function has only one output.

Answer 3

A function is a mapping from elements in one set to another set. The "from" set is called the domain, and the "to" set is called the range.

f: Z -> Z (f maps integers to integers)
f: R -> C (f maps reals to complex numbers)
f: R -> {0,1} (f maps real numbers to either 0 or 1)
f: R -> {red, green, blue} (f maps real numbers to either red, green or blue)

We can also combine sets to create multi-dimensional sets

Z x Z := two tuple of integers (1,1) ; ( 2,2) , (1,3)
R x R x R := three tuple of real numbers (1.2, 1.5, 3.14159...) ; etc....

It also makes sense to talk about functions mapping from a set of tuples to a set of tuples.

f: Z x Z -> Z (mapping two tuples of integers to integer)
f: Z -> Z x Z ( mapping integers to two tuples)

tl;dr When you talk about functions which outputs mulitple arguments, you're really talking about functions which outputs a single element which is an n-tuple.