A sublinear function (or functional, as is more often used in functional analysis), in linear algebra and related areas of mathematics, is a function on a vector space V over an ordered field (e.g. the real numbers ), which satisfies
- for any positive and any (positive homogeneity), and
- for any x, y ∈ V (subadditivity).
This means that for any linear function for sufficiently large input grows slower than
- Every (semi-)norm is a sublinear function. The opposite is not true, because (semi-)norms can have their domain vector space over any field (not necessarily ordered) and must have as their codomain.
The concept can be extended to operators that are homogeneous and subadditive. This requires only that the codomain be, say, an ordered vector space to make sense of the conditions.
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