Both are the same thing (kind of)
Re:Free energy principle
by throwaway37585 on Monday July 23, 2018 @11:47AM
(#17593537)
The name “functional” is commonly used to refer to a function which takes a whole function (rather than, say, a number) as input. A simple example of a functional is the definite integral (area under the curve) over an interval.
I think what is confusing people (it is certainly confusing me) is the distinction between a function and a functional.