Bs space - Wikipedia

In the mathematical field of functional analysis, the space bs consists of all infinite sequences (x_i) of real numbers $\mathbb {R}$ or complex numbers $\mathbb {C}$ such that $\sup _{n}\left|\sum _{i=1}^{n}x_{i}\right|$ is finite. The set of such sequences forms a normed space with the vector space operations defined componentwise, and the norm given by $\|x\|_{bs}=\sup _{n}\left|\sum _{i=1}^{n}x_{i}\right|.$

Furthermore, with respect to metric induced by this norm, bs is complete: it is a Banach space.

The space of all sequences $\left(x_{i}\right)$ such that the series $\sum _{i=1}^{\infty }x_{i}$ is convergent (possibly conditionally) is denoted by cs. This is a closed vector subspace of bs, and so is also a Banach space with the same norm.

The space bs is isometrically isomorphic to the Space of bounded sequences $\ell ^{\infty }$ via the mapping $T(x_{1},x_{2},\ldots )=(x_{1},x_{1}+x_{2},x_{1}+x_{2}+x_{3},\ldots ).$

Furthermore, the space of convergent sequences c is the image of cs under $T.$

References

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Dunford, N.; Schwartz, J.T. (1958), Linear operators, Part I, Wiley-Interscience.

v t e Banach space topics
Types of Banach spaces	Asplund Banach list Banach lattice Grothendieck Hilbert Inner product space Polarization identity (Polynomially) Reflexive Riesz L-semi-inner product (B Strictly Uniformly) convex Uniformly smooth (Injective Projective) Tensor product (of Hilbert spaces)
Banach spaces are:	Barrelled Complete F-space Fréchet tame Locally convex Seminorms/Minkowski functionals Mackey Metrizable Normed norm Quasinormed Stereotype
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Analysis	Abstract Wiener space Banach manifold bundle Bochner space Convex series Differentiation in Fréchet spaces Derivatives Fréchet Gateaux functional holomorphic quasi Integrals Bochner Dunford Gelfand–Pettis regulated Paley–Wiener weak Functional calculus Borel continuous holomorphic Measures Lebesgue Projection-valued Vector Weakly / Strongly measurable function
Types of sets	Absolutely convex Absorbing Affine Balanced/Circled Bounded Convex Convex cone (subset) Convex series related ((cs, lcs)-closed, (cs, bcs)-complete, (lower) ideally convex, (Hx), and (Hwx)) Linear cone (subset) Radial Radially convex/Star-shaped Symmetric Zonotope
Subsets / set operations	Affine hull (Relative) Algebraic interior (core) Bounding points Convex hull Extreme point Interior Linear span Minkowski addition Polar (Quasi) Relative interior
Examples	Absolute continuity AC $ba(\Sigma )$ c space Banach coordinate BK Besov $B_{p,q}^{s}(\mathbb {R} )$ Birnbaum–Orlicz Bounded variation BV Bs space Continuous C(K) with K compact Hausdorff Hardy H^p Hilbert H Morrey–Campanato $L^{\lambda ,p}(\Omega )$ ℓ^p $\ell ^{\infty }$ L^p $L^{\infty }$ weighted Schwartz $S\left(\mathbb {R} ^{n}\right)$ Segal–Bargmann F Sequence space Sobolev W^k,p Sobolev inequality Triebel–Lizorkin Wiener amalgam $W(X,L^{p})$
Applications	Differential operator Finite element method Mathematical formulation of quantum mechanics Ordinary Differential Equations (ODEs) Validated numerics

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