本帖最后由 厚积薄发 于 2010-1-26 21:12 编辑 " w2 M: Y: m' m s- A9 O! J/ s* i
" h% Z# O- g" Y" o: N* CIn mathematics, a functional is traditionally a map from a vector space to the field underlying the vector space, which is usually the real numbers. In other words, it is a function that takes a vector as its argument or input and returns a scalar. Its use goes back to the calculus of variations where one searches for a function which minimizes a certain functional. A particularly important application in physics is to search for a state of a system which minimizes the energy functional., n$ t- K B7 i$ j$ ?
In functional analysis, the functional is also used in a broader sense as a mapping from an arbitrary vector space into the underlying scalar field (usually, real or complex numbers). A special kind of such functionals, linear functionals, gives rise to the study of dual spaces. 6 H- U( I" e4 h0 ITransformations of functions is a somewhat more general concept, see operator.