Editing Functional (mathematics) (section)

==Derivative and integration==
{{see also|Calculus of variations}}
[[Functional derivative]]s are used in [[Lagrangian mechanics]]. They are derivatives of functionals; that is, they carry information on how a functional changes when the input function changes by a small amount.

[[Richard Feynman]] used [[Functional integration|functional integrals]] as the central idea in his [[Path integral formulation|sum over the histories]] formulation of [[quantum mechanics]]. This usage implies an integral taken over some [[function space]].