Math 2.0

definition

Bounded sequence

Definition

Let (an)(a_n) be a real sequence. The sequence is bounded above if there is a real number MM with an≤Ma_n \le M for all n∈Nn \in \mathbb{N}. The sequence is bounded below if there is a real number mm with an≥ma_n \ge m for all n∈Nn \in \mathbb{N}. The sequence is bounded if it is bounded above and bounded below. Equivalently, (an)(a_n) is bounded if there is a real number K≥0K \ge 0 with ∣an∣≤K|a_n| \le K for all n∈Nn \in \mathbb{N}.

Remarks

The sequence an=(−1)na_n = (-1)^n is bounded, with K=1K = 1. The sequence an=na_n = n is bounded below by 00, but it is not bounded above. A sequence is a function on N\mathbb{N}, so a bounded sequence is a bounded function on N\mathbb{N}. Each convergent sequence is bounded, as the node convergent sequences are bounded states.

Explanations

L1 human

A sequence is bounded when all its terms stay inside one fixed interval [−K,K][-K, K]. The terms can move up and down, but they never escape from that interval.

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  1. Sequence definition
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Sources

  1. Web https://en.wikipedia.org/wiki/Sequence, Bounded
  2. Web https://en.wikipedia.org/wiki/Bounded_function, lead section