Definition:Bounded Below Sequence

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This page is about sequences which are bounded below. For other uses, see Definition:Bounded Below.

Definition

Let $\left({T, \preceq}\right)$ be an ordered set.

Let $\left \langle {x_n} \right \rangle$ be a sequence in $T$.


Then $\left \langle {x_n} \right \rangle$ is bounded below if and only if:

$\exists m \in T: \forall i \in \N: m \preceq x_i$


Real Sequence

The concept is usually encountered where $\left({T, \preceq}\right)$ is the set of real numbers under the usual ordering $\left({\R, \le}\right)$:


Let $\sequence {x_n}$ be a real sequence.


Then $\sequence {x_n}$ is bounded below if and only if:

$\exists m \in \R: \forall i \in \N: m \le x_i$


Unbounded Below

$\left \langle {x_n} \right \rangle$ is unbounded below iff there exists no $m$ in $T$ such that:

$\forall i \in \N: m \preceq x_i$


Also see