Definition:Positive Part

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Definition

Let $X$ be a set.

Let $f: X \to \overline \R$ be an extended real-valued function.


Then the positive part of $f$, $f^+: X \to \overline \R$, is the extended real-valued function defined by:

$\forall x \in X: \map {f^+} x := \max \set {0, \map f x}$

where the maximum is taken with respect to the extended real ordering.


That is:

$\forall x \in X: \map {f^+} x := \begin {cases} \map f x & : \map f x \ge 0 \\ 0 & : \map f x < 0 \end {cases}$


Also defined as

Some sources insist that $f$ be a real-valued function instead.

However, $\R \subseteq \overline \R$ by definition of $\overline \R$.

Thus, the definition given above incorporates this approach.


Also see


Sources