Space of bounded sequences
In the mathematical field of functional analysis, the space denoted by c is the vector space of all convergent sequences
of real numbers or complex numbers. When equipped with the uniform norm:
![{\displaystyle \|x\|_{\infty }=\sup _{n}|x_{n}|}](https://wikimedia.org/api/rest_v1/media/math/render/svg/895a7837455f2d2dca7d05b922198903e823e683)
the space
becomes a Banach space. It is a closed linear subspace of the space of bounded sequences,
, and contains as a closed subspace the Banach space
of sequences converging to zero. The dual of
is isometrically isomorphic to
as is that of
In particular, neither
nor
is reflexive.
In the first case, the isomorphism of
with
is given as follows. If
then the pairing with an element
in
is given by
![{\displaystyle x_{0}\lim _{n\to \infty }y_{n}+\sum _{i=0}^{\infty }x_{i+1}y_{i}.}](https://wikimedia.org/api/rest_v1/media/math/render/svg/ba6d8da89b66ce54444e4ffb2d67477c194ff1fb)
This is the Riesz representation theorem on the ordinal
.
For
the pairing between
in
and
in
is given by
![{\displaystyle \sum _{i=0}^{\infty }x_{i}y_{i}.}](https://wikimedia.org/api/rest_v1/media/math/render/svg/4714f45d3d745f4d0719ef847621bf15340bbb6a)