A 'function' is a mapping from a space of numbers to another space of numbers. A mathematical object known as a 'functional' is a mapping of a space of functions
to a number. A definite integral is one such example of a functional.[1] [2]
- ↑ Landau, L.D. and Lifshitz, E.M., 1976. Mechanics, vol. 1. Course of theoretical physics, pp.84-93.
- ↑ Fox, C., 1950. An introduction to the calculus of variations. Courier Corporation.