**Calculus of variations** is a field of

mathematical analysis that deals with maximizing or minimizing

functionals, which are

mappings from a set of

functions to the

real numbers. Functionals are often expressed as

definite integrals involving functions and their

derivatives. The interest is in

*extremal* functions that make the functional attain a maximum or minimum value – or

*stationary* functions – those where the rate of change of the functional is zero.