functional

An example of a linear functional on the space C₀(R) of continuous functions on R that tend to 0 is φ(f)=f(0) ("substitution"). An example of a nonlinear functional is the variation of f.

Func"tion*al (?), a.

1.

Pertaining to, or connected with, a function or duty; official.

2. Physiol.

Pertaining to the function of an organ or part, or to the functions in general.

Functional disease Med., a disease of which the symptoms cannot be referred to any appreciable lesion or change of structure; the derangement of an organ arising from a cause, often unknown, external to itself opposed to organic disease, in which the organ itself is affected.

© Webster 1913.