Definition:Lower Darboux Sum/Rectangle
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Definition
Let $R$ be a closed rectangle in $\R^n$.
Let $f : R \to \R$ be a bounded real-valued function.
Let $P$ be a finite subdivision of $R$.
Let $S$ be the set of subrectangles of $P$.
For every:
- $r = \closedint {a_1} {b_1} \times \dotso \times \closedint {a_n} {b_n} \in S$
define:
- $\ds m_r^{\paren f} = \inf_{x \mathop \in r} \map f x$
- $\ds \map v r = \prod_{1 \mathop \le i \mathop \le n} \paren {b_i - a_i}$
Then:
- $\ds \map {L^{\paren f}} P = \sum_{r \mathop \in S} m_r^{\paren f} \map v r$
is called the lower Darboux sum of $f$ on $R$ with respect to $P$.
If there is no ambiguity as to what function is under discussion, $m_r$ and $\map L P$ are usually used.