Bounded set: Difference between revisions
imported>Richard Pinch (fix link) |
imported>Richard Pinch m (→Theorems about bounded sets: link) |
||
| Line 9: | Line 9: | ||
==Theorems about bounded sets== | ==Theorems about bounded sets== | ||
Every bounded set of [[real number]]s has a [[supremum]] and an [[infimum]]. It follows that a | Every bounded set of [[real number]]s has a [[supremum]] and an [[infimum]]. It follows that a [[monotonic sequence]] of real numbers that is bounded has a [[limit of a sequence|limit]]. A bounded sequence that is not monotonic does not necessarily have a limit, but it has a [[subsequence]] that does have a limit (this is the [[Bolzano–Weierstrass theorem]]). | ||
The [[Heine–Borel theorem]] states that a subset of the [[Euclidean space]] '''R'''<sup>''n''</sup> is [[compact space|compact]] if and only if it is [[closed set|closed]] and bounded. | The [[Heine–Borel theorem]] states that a subset of the [[Euclidean space]] '''R'''<sup>''n''</sup> is [[compact space|compact]] if and only if it is [[closed set|closed]] and bounded. | ||
Revision as of 14:55, 12 November 2008
In mathematics, a bounded set is any subset of a normed space whose elements all have norms which are bounded from above by a fixed positive real constant. In other words, all its elements are uniformly bounded in magnitude.
Formal definition
Let X be a normed space with the norm . Then a set is bounded if there exists a real number M > 0 such that for all .
Theorems about bounded sets
Every bounded set of real numbers has a supremum and an infimum. It follows that a monotonic sequence of real numbers that is bounded has a limit. A bounded sequence that is not monotonic does not necessarily have a limit, but it has a subsequence that does have a limit (this is the Bolzano–Weierstrass theorem).
The Heine–Borel theorem states that a subset of the Euclidean space Rn is compact if and only if it is closed and bounded.