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Completeness (mathematics)

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In mathematics, completeness is a property ascribed to a metric space in which every Cauchy sequence in that space is convergent. In other words, every Cauchy sequence in the metric space tends in the limit to a point which is again an element of that space. Hence the metric space is, in a sense, "complete."

Formal definition

Let X be a metric space with metric d. Then X is complete if for every Cauchy sequence x_1,x_2,\ldots \in X there is an associated element x \in X such that \mathop{\lim}_{n \rightarrow \infty} d(x_n,x)=0.

See also

Banach space

Hilbert space

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