Continuous extension of functions from countable sets

Analytical expressions for power spectral density issued from one-dimensional continuous piecewise linear maps with three slopes

We give an expression for the most general continuous linear input-output map that takes the space of (Lebesgue) integrable functions into itself. This expression is a function-space limit of an integral. As an application, a representation result is given for an important family of linear maps that take the space of bounded measurable functions into itself and satisfy a certain continuity condition, and it is noted that no such result holds for a general continuous linear maps that takes the space into itself and meets the continuity condition. Some related material concerning engineering education is also given.

We characterize the pairs of Moscatelli Frechet and spaces such that: 1) Every continuous linear map from E into F sends bounded sets in E into precompact ones in F. 2) Every bounded map from E into F sends some 0-neighbourhood in E into a precompact set in F.

For the Fr'{e}chet algebras $(A, (p_k))$ and $(B, (q_k))$ and $n in mathbb{N}$, $ngeq 2$, a linear map $T:A rightarrow B$ is called textit{almost $n$-multiplicative}, with respect to $(p_k)$ and $(q_k)$, if there exists $varepsilongeq 0$ such that$$q_k(Ta_1a_2cdots a_n-Ta_1Ta_2cdots Ta_n)leq varepsilon p_k(a_1) p_k(a_2)cdots p_k(a_n),$$for each $kin mathbb{N}$ and $a_1, a_2, ldots, a_nin A$. The linear map $T$ is called textit{weakly almost $n$-multiplicative}, if there exists $varepsilongeq 0$ such that for every $kin mathbb{N}$ there exists $n(k)in mathbb{N}$ with$$q_k(Ta_1a_2cdots a_n-Ta_1Ta_2cdots Ta_n)leq varepsilon p_{n(k)}(a_1) p_{n(k)}(a_2)cdots p_{n(k)}(a_n),$$for each $k in mathbb{N}$ and $a_1, a_2, ldots, a_nin A$.The linear map $T$ is called $n$-multiplicative if$$Ta_{1}a_{2} cdots a_{n} = Ta_{1} Ta_{2} cdots Ta_{n},$$for every $a_{1}, a_{2},ldots, a_{n} in A$.In this paper, we investigate automatic continuity of (weakly) almost $n$-multiplicative maps between certain classes of Fr'{e}chet algebras, including Banach algebras. We show that if $(A, (p_k))$ is a Fr'{e}chet algebra and $T: A rightarrow mathbb{C}$ is a weakly almost $n$-multiplicative linear functional, then either $T$ is $n$-multiplicative, or it is continuous. Moreover, if $(A, (p_k))$ and $(B, (q_k))$ are Fr'{e}chet algebras and $T:A rightarrow B$ is a continuous linear map, then under certain conditions $T$ is weakly almost $n$-multiplicative for each $ngeq 2$. In particular, every continuous linear functional on $A$ is weakly almost $n$-multiplicative for each $ngeq 2$.

A theory of test function spaces is developed. These are generalizations of test function spaces of type Hμ. The elements of the dual spaces are called ultradistributions, It is shown that the Hankel transformation hμ for μ≧−1/2 is a continuous linear mapping from each of these spaces into certain spaces of the above type. The generalized Hankel transformation hμ′ is defined as a continuous linear mapping between the dual spaces. Hankel transformations of arbitrary order and also of arbitrary growth are studied. The theory thus developed is applied to prove a uniqueness theorem for the Cauchy problem for the operator Sμ.

<abstract><p>In this paper, we show that every continuous linear map between unital $ C^\ast $-algebras is skew Lie triple derivable at the identity is a $ \ast $-derivation and that every continuous linear map between unital $ C^\ast $-algebras which is a skew Lie triple homomorphism at the identity is a Jordan $ \ast $-homomorphism.</p></abstract>

A linear map $T$ from a Banach algebra $A$ into another $B$ preserves zero products if $T(a)T(b)=0$ whenever $a,b\in A$ are such that $ab=0$. This paper is mainly concerned with the question of whether every continuous linear surjective map $T\colon A\rig

On spaces of continuous linear mappings between locally convex spaces

Surjective linear maps preserving local spectra

In this paper, we study the representation of orthogonally additive mappings acting on Hilbert C*-modules and Hilbert H*-modules. One of our main results shows that every continuous orthogonally additive mapping f from a Hilbert module W over K(H) or HS(H) to a complex normed space is of the form f(x)=T(x)+S( ) for all x in W, where T is a continuous additive mapping, and S is a continuous linear mapping.

Finiteness spaces constitute a categorical model of Linear Logic (LL) whose objects can be seen as linearly topologised spaces, (a class of topological vector spaces introduced by Lefschetz in 1942) and morphisms as continuous linear maps. First, we recall definitions of finiteness spaces and describe their basic properties deduced from the general theory of linearly topologised spaces. Then we give an interpretation of LL based on linear algebra. Second, thanks to separation properties, we can introduce an algebraic notion of totality candidate in the framework of linearly topologised spaces: a totality candidate is a closed affine subspace which does not contain 0. We show that finiteness spaces with totality candidates constitute a model of classical LL. Finally, we give a barycentric simply typed lambda-calculus, with booleans \({\mathcal{B}}\) and a conditional operator, which can be interpreted in this model. We prove completeness at type \({\mathcal{B}}^n\to{\mathcal{B}}\) for every n by an algebraic method.KeywordsTopological Vector SpaceLinear LogicProduct TopologyContinuous Linear FunctionCompact Open TopologyThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

It is well-known that the algebraic tensor product E ⊗ Y of a not necessarily locally convex topological vector space E and a locally convex space Y can be identified with a subspace of the so-called e-product EeY (a space of continuous linear mappings from Y′ into E). So, whenever EeY is complete, even the completed tensor product is (isomorphic to) a subspace of EeY. As this occurs in many important cases, it is interesting to remark that, for each continuous linear operator u from a locally convex space F into E, there exists a locally convex U with continuous embedding j∶U→E and a continuous linear map u∶F→U such that u=j·u. As main applications of a combination of these ideas, we obtain a characterization of the functions in as continuous functions with values in locally convex spaces (this gives new aspects for the intergration theory of Gramsch [5]) and a result extending a theorem in [6] on holomorphic functions with values in non locally convex spaces to arbitrary complex manifolds.

We suggest to model the electrical activity of an isolated neuron by using piecewise linear stochastic and piecewise continuous dynamic maps based on phenomenological notions about neuron dynamics. It is demonstrated that the proposed models provide for time series qualitatively similar to those observed in experiments with biological neurons. The possibility of using these models for constructing coupled neuron systems is discussed.

Linear maps preserving G-unitary operators in Hilbert space

Let $G$ be a locally compact amenable group. The goal of this paper is to investigate the problem of surjective zero products preserving maps from the Fourier algebra of $G$ into a completely contractive Banach algebra. We show that if $B$ is a completely contractive Banach algebra which is faithful and factors weakly, then every surjective completely bounded linear map from $A(G)$ into $B$ which preserves zero products is a weighted homomorphism. Moreover an equivalent condition is given for such a map to be a homomorphism. In particular, this result implies that if $B$ is a commutative C$^*$-algebra or a matrix space and $T:A(G)\rightarrow B$ is a continuous surjective linear map which preserves zero products, then $T$ is a weighted homomorphism and there is an equivalent condition for $T$ to be a homomorphism.