different between subadditivity vs subadditive

English

sub- +? additivity

subadditivity (countable and uncountable, plural subadditivities)

(uncountable) The state of being subadditive.
The statement that a function is subadditive.
An outer measure $\mu ^{*}$ satisfies a property called “subadditivity”, viz.: $\mu ^{*}{\big (}\bigcup _{j=1}^{\infty }A_{j}{\big )}\leq \sum _{j=1}^{\infty }\mu ^{*}(A_{j})$ . If the less-than-or-equal sign were replaced with an equal sign then the property would be “additivity” instead.

sub- +? additive

subadditive (not comparable)

(of a function) Such that the image of a sum is at most the sum of the images of the summands.
The square-root function is subadditive under addition because ${\sqrt {a+b}}\leq {\sqrt {a}}+{\sqrt {b}}$ .

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