Banach space


Also found in: Wikipedia.

Banach space

[′bä‚näk ‚spās]
(mathematics)
A real or complex vector space in which each vector has a non-negative length, or norm, and in which every Cauchy sequence converges to a point of the space. Also known as complete normed linear space.

Banach Space

 

(named after S. Banach), a complete normed linear space.

Banach space

(mathematics)
A complete normed vector space. Metric is induced by the norm: d(x,y) = ||x-y||. Completeness means that every Cauchy sequence converges to an element of the space. All finite-dimensional real and complex normed vector spaces are complete and thus are Banach spaces.

Using absolute value for the norm, the real numbers are a Banach space whereas the rationals are not. This is because there are sequences of rationals that converges to irrationals.

Several theorems hold only in Banach spaces, e.g. the Banach inverse mapping theorem. All finite-dimensional real and complex vector spaces are Banach spaces. Hilbert spaces, spaces of integrable functions, and spaces of absolutely convergent series are examples of infinite-dimensional Banach spaces. Applications include wavelets, signal processing, and radar.

[Robert E. Megginson, "An Introduction to Banach Space Theory", Graduate Texts in Mathematics, 183, Springer Verlag, September 1998].
References in periodicals archive ?
Let ([OMEGA], [SIGMA], [mu]) be a complete probability measure space and Y a nonemptysubset of a separable Banach space E.
The results about the BVP with multiple point boundary conditions of impulsive p-Laplacian operator fractional differential equations are few, especially in Banach space.
E is a nonreflexive Banach space, [sup.c][D.sup.[alpha].sub.0+] denotes the fractional Caputo derivative, [mathematical expression not reproducible] are given functions satisfying some assumptions that will be specified later, the integral is understood to be the Henstock-Kurzweil-Pettis, and solutions to (5) will be sought in E = C(I, [E.sub.[omega]]).
Certain deficiencies of the descriptions (established in [1]) of the Carleman classes of vectors, in particular the Gevrey classes, of a scalar type spectral operator in a complex Banach space inadvertently overlooked by the author when proving the results of the three papers [2-4] are observed not to affect the validity of the latter due to more recent findings of [5].
A [C.sub.0]-quasisemigroup R(t, s) on Banach space X is said to be uniformly exponentially stable if there exist constants [alpha] > 0 and N [greater than or equal to] 1 such that
Throughout X denotes a real Banach space, X*, the dual of X, [B.sub.X] = {x [member of] X : [parallel]x[parallel] [less than or equal to] 1} and [S.sub.X] = {x [member of] X : [parallel]x[parallel] = 1}, the unit sphere of X.
Recall that the right-hand quotient Ao[B.sup.-1] of two operator ideals A and B is the operator ideal that consists of all operators T [member of] L(X,Y) such that TS [member of] A ([X.sub.0],Y) whenever S [member of] B([X.SUB.0],X) for some Banach space [X.sub.0] (see [6,3.1.1]).
Suppose X is a Banach space equipped with the norm topology (denoted by ||*||) as well as the weak topology (denoted by [T.sub.w]).
In this article we present a fractional quantitative Korovkin type approximation theory for linear operators involving Banach space valued functions.
It is induced on a Banach space by a skew-evolution cocycle (see [13]) defined over a semiflow associated with a generalized dynamical system.
Where [mathematical expression not reproducible] and f : J x E x E x [OMEGA] [right arrow] E are given continuous functions, ([OMEGA], A, v) is a measurable space, and E is a real (or complex) Banach space with norm [[parallel] * [parallel].sub.e] and dual [E.sup.*], such that E is the dual of a weakly compactly generated Banach space [mathematical expression not reproducible], is the left-sided mixed Hadamard integral of order r, and [mathematical expression not reproducible] is a given continuous and measurable function such that