Questions tagged [topological-vector-spaces]

A topological vector space is a vector space $V$ over a topological field $\mathbb{K}$ (typically $\mathbb{K}=\mathbb{R}$ or $\mathbb{K}=\mathbb{C}$), together with a topology on $V$ such that vector addition and scalar multiplication are both continuous. Hilbert spaces and Banach spaces are examples of topological vector spaces.

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Generalized Jensen's inequality for positively homogeneous functions

The function $f:V \to \hat{\mathbb{R}}$ is said to be positively homogeneous iff $f(\alpha v) = \alpha f(v)$ for every $\alpha \in \mathbb{R}_{++}$. Here $V$ is a real vector space and $\hat{\mathbb{R}...
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An explicit description for a certain type of infinite-dimensional homogeneous polynomials

This is a side question from Infinite-dimensional "algebraic varieties", and I have also asked it on MSE without getting any response. Denote by $X_p$ ($1 \le p \le \infty$) the Banach ...
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Fundamental result on the projective tensor product of sections of a vector bundle

Definition Let $E_{1} \xrightarrow{\pi_{1}} M_{1}$, $E_{2} \xrightarrow{\pi_{2}} M_{2}$ be two vector bundles over $M_{1}$ and $M_{2}$ with fibers $V_{1}$, $V_{2}$ respectively. The exterior tensor ...
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Looking for an electronic copy of Trèves and Martineau books

I would like to know if anyone has an electronic copy of the following books: MR0177291 Martineau, A.; Trèves, F. Éléments de la théorie des espaces vectoriels topologiques et des distributions. Fasc....
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5 votes
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Topological localisations of algebras and solidification

Let $A$ be a (topologically discrete) commutative ring and consider the topological ring $A((z))$. Let $\underline{A((z))}$ denote the corresponding condensed ring, and let $a(z)$ be a non-zero ...
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Is a convex, lower semicontinuous function that is bounded from below, actually continuous?

While thinking about convex functions, I managed to put together the following proof which I find a bit too good to be true. $X$ is a topological vector space that is also a Baire space. Lemma: Let $f ...
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Aronszajn-Gagliardo Theorem: case of exponent $\theta$ (Exercise 2.8.4 from Bergh-Löfström)

I'm working on the book "Interpolation Spaces" by Bergh and Löfström. I'm interested in solving the exercise 2.8.4 on page 33. which asks: Let $A$ be an interpolation space of exponent $\...
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Pontryagin-reflexivity of spaces of continuous functions

It is well-known that a Banach space $V$ is always Pontryagin-reflexive, i.e. the natural map $V\to \text{Hom}_\mathbb{R}(\text{Hom}_\mathbb{R}(V, \mathbb{R}), \mathbb{R})$, where $\text{Hom}_\mathbb{...
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Fundamental biorthogonal systems in barreled spaces

Let $X$ be a barreled vector space (over the field of real or complex numbers), $X'$ its topological dual space, and $\langle\cdot,\cdot\rangle$ the canonical bilinear form on $X \times X'$. ...
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When is a natural map between completions injective?

Let $X$ be a vector space equipped with a norm $p$ and a seminorm $q$. Denote the completion of $X$ with respect to $p$ with $X_p$ and with respect to $p+q$ by $X_{p+q}$. Then the induced map $\iota : ...
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Reference on inductive (direct) limit of ordered vector spaces and vector lattices

I looked in all textbooks on vector lattices (Riesz spaces) as well as ordered vector spaces, but couldn't find any mentions of neither inductive nor projective limit for these structures. Googling ...
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Sequential separability on $C_p(X)$

Definition. Let $E$ be a topological space. Suppose that $E$ contains a sequence $\{x_n\}$ such that for every $x\in E$, there exists a subsequence $\{x_{n_k}\}$ of $\{x_n\}$ with $x=\lim x_{n_k}$. ...
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Why is the space of smooth sections complete?

This page is about the space of sections: Let $E \stackrel{\mathrm{fb}}{\rightarrow} \Sigma$ be a smooth vector bundle. On its real vector space $\Gamma_{\Sigma}(E)$ of smooth sections consider the ...
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201 views

An approximation property in a separable topological vector space

Let $X$ be a topological vector space. Let us say that $X$ enjoys sequential separablity if there exists a sequence $\{x_n\}$ in $X$ such that for every $x\in X$ there exists a subsequence of $\{...
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Extending a $\sigma$-weakly continuous map: Takesaki IV.5.13

Consider the following fragment from chapter IV in Takesaki's book "Theory of operator algebra I": Why is the boxed line true? Takesaki argues that $$\theta_0: \mathscr{M}_1\otimes_{\...
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Predual theorem proof in Takesaki's volume I

Consider the following fragment from Takesaki's book "Theory of operator algebra I" (Section III.3 ,p133-134). Why is the boxed line true? I can see that $\epsilon: \widetilde{A}\to A$ is ...
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Borel sigma algebra coming from the weak topology on TVS

Let $(X,\tau)$ be a topological vector space. Suppose that, there is a sequence of subsets $X_n\subseteq X$ with, For every $n\in \mathbb{N}$, the topology $\tau$ on $X_n$ is second countable and ...
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3 votes
1 answer
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$\varepsilon$-product in Bierstedt's paper

I am reading K.D.Bierstedt's paper Gewichtete Räume stetiger vektorwertiger Funktionen und das injektive Tensorprodukt. I. Journal für die reine und angewandte Mathematik 259 (1973): 186-210. It is ...
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5 votes
2 answers
273 views

Product of inductive limit topologies on $C_c(X)\times C_c(X)$

I have a stupid question about a topology on $C_c(X)$. Here $X$ is locally compact Hausdorff. Can assume $\sigma$-compact if it helps. Definition (topology on $C_c(X)$): For each compact $K \subset X$,...
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Approximation of a linear functional by linear continuous functionals

Let $X$ be a locally convex space, $T$ a balanced convex compact set in $X$, and $f:X\to\mathbb{C}$ a linear functional which is (not necessarily continuous on $X$, but) continuous on $T$. It is not ...
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6 votes
1 answer
201 views

Is the projectivization of a topological vector space Tychonoff?

Let $E$ be a locally convex topological vector space over $\mathbb{R}$. The projectivization $PE$ is the quotient of $E\backslash\{0_{E}\}$ with respect to the equivalence relation $e\sim f$ if $e=\...
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Definition of infinite-dimensional Gaussian random variable

For infinite-dimensional Gaussian measures, we often see the definition of Gaussian random variables like this: Let $H(\Omega;\mathbb{R})$ be a separable Hilbert space. A random variable $u \in H$ is ...
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A Fréchet space characterization of smooth structures on topological spaces?

For a compact manifold $M$ the space of smooth functions $C^{\infty}(M)$ is a Fréchet space where the seminorms are the suprema of the norms of all partial derivatives. Is there some way to ...
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6 votes
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101 views

Cech cohomology on product covers & Fréchet sheaves

My question is about the paper [Ka67]. Let $S, T$ be sheaves of nuclear Fréchet spaces over paracompact topological spaces $X, Y$, respectively; in particular, if $V \subset U$ are open subsets in $X$,...
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542 views

Condensed/liquid vector spaces and path integrals

[Edited to take into account comments.] Background One approach to the problem of making rigorous various measures on spaces of paths (for example, the Wiener or Feynman measure) is the time-slicing ...
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Nested nets of closed bounded star-shaped sets in a semi-reflexive space

Among Hausdorff locally convex spaces, semi-reflexivity is characterized by the weak topology having the Heine-Borel property. It follows that, in a semi-reflexive space, every nested net of closed ...
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1 answer
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Uniqueness of the predual of a W*-algebra

Consider the following fragments in Takesaki's "Theory of operator algebras" (volume I): Question: So, we have an abstract Banach space $F$ with $A \cong F^*$. In Lemma 3.6, one considers ...
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1 answer
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About $\sigma$ strong$^*$-functionals and seminorms

I'm reading the book "Theory of operator algebras" by Takesaki. In this book, the $\sigma$-strong$^*$ topology on the space $B(H)$ (bounded operators on the Hilbert space $H$) is defined (...
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About the normability of the space of continuous functions

Let $A$ be a subset of $\mathbb{R}^n$, and denote by $C(A)$ the space of complex-valued continuous functions defined on $A$. We know that if $A$ is compact then we can define a norm on $C(A)$ so that ...
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1 answer
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Strict topology on the multiplier algebra

Let $A$ be a $C^*$-algebra. Let $M(A)$ be its multiplier $C^*$-algebras. The strict topology on $M(A)$ is given by $$x_\lambda \to x \iff \forall a\in A: (\|x_\lambda a-xa\| + \|ax_\lambda - ax\| \to ...
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1 vote
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Effect of dualization of density

Let $D\subset X$ be a dense subset of a complete separable locally convex space $X$ over $\mathbb{R}$. Though the question seems simple enough, I can't seem to find the answer in the literature: If $...
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8 votes
0 answers
178 views

On "linearly independent" metric spaces

Urysohn's universal metric space $\Bbb U$ satisfies the following surprising property: Whenever $i\colon\Bbb U\to E$ is an isometric embedding into a normed vector space such that $0\not\in i(\Bbb U)$...
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1 vote
2 answers
273 views

Topologies on space of compactly supported continuous functions

Let $X$ be a locally compact Hausdorff space. As far as I understand, the space $C_c(X) = C_c(X; \mathbb{C})$ of compactly supported continuous complex-valued functions on $X$ is (most?) often ...
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6 votes
1 answer
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Is the tensor product of distributions a continuous bilinear map with respect to the weak topology?

Let $X$ and $Y$ be smooth manifolds. The map $\mathcal{D}'(X)\times\mathcal{D}'(Y)\to\mathcal{D}'(X\times Y)$ given by $(S,T)\mapsto S\boxtimes T$ is continuous with respect to the strong topology. Is ...
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2 votes
1 answer
155 views

Biorthogonal weakly null basic sequences

Let $E$ be a Banach space, let $e_{n}\in E$ and $g_{n}\in E^{*}$ be biorthogonal basic sequences (i.e. $\left<e_n,g_m\right>=\delta_{mn}$ ). Moreover, both of these sequences are weakly null. (...
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5 votes
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Logarithm on formal power series continuous?

Denote $V:=\mathbb{R}^d$ and consider the Cartesian product $V^\infty:=\prod_{k=0}^\infty V^{\otimes k}$ together with its canonical projections $\pi_k : V^\infty\rightarrow V^{\otimes k}, (v_0, v_1, \...
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5 votes
1 answer
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The tensor product of two topological complexes with closed range

A Künneth formula by Grothendieck/Schwartz states the following: Let $A, B$ be chain complexes of nuclear Fréchet spaces. If the differentials $d_A, d_B$ are topological homomorphisms (meaning in ...
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1 vote
1 answer
116 views

What's the size of non standard monad for weak topology?

There have been several works characterizing weak topology by nonstandard analysis, which give rise to the following monad ($X$ is a Hilbert space): $$\mu(0) = \{y\in{}^{*}X: \forall x\in X ~~ \...
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7 votes
0 answers
388 views

Infinite-dimensional affine space in algebraic geometry and algebraic topology

In topology, there are of course many different infinite-dimensional topological vector spaces over $\mathbb R$ or $\mathbb C$. Luckily, in algebraic topology, one rarely needs to worry too much about ...
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2 votes
1 answer
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Is $C_0(X) $ Frechet-Urysohn with respect to the compact-open topology?

Recall that a topological space is called Frechet-Urysohn if the operations of closure and sequential closure coincide. Let $X$ be a locally compact Hausdorff space. It is known that $C(X)$ is not ...
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2 answers
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$(ST)_{[13]}= S_{[13]}T_{[13]}$ for $S,T \in B(\mathcal{H}\otimes \mathcal{H}).$

Let $T\in B(\mathcal{H} \otimes \mathcal{H})$ where $\mathcal{H}$ is a Hilbert space. We can define operators $$T_{[12]}= T \otimes 1;\quad T_{[23]}= 1 \otimes T$$ and if $\Sigma: \mathcal{H} \otimes \...
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5 votes
2 answers
233 views

Is there a topology that makes every basic sequence null?

Let $E$ be a Banach space. Let $F$ be the collection of all $f\in E^*$ such that $\left<f,e_n\right>\to 0$, for every normalized basic sequence $\{e_n\}$. It is easy to see that $F$ is a closed ...
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1 vote
1 answer
204 views

Is a topology sandwiched between two norms compactly generated?

Recall that a Hausdorf topological space $X$ is called compactly generated if any set whose intersections with compacts are compact is closed. Locally compact and first countable spaces are compactly ...
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3 votes
0 answers
42 views

Continuous differentiations of functional algebras

Let $A$ be some algebra (infinite-dimensional) of analytic functions on $\mathbb{C}^n$, and $D$ be some derivation of $A$, i.e. $D(fg)=Df \cdot g + f \cdot Dg)$ (so A may be considered as a ...
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9 votes
1 answer
214 views

Is a Banach lattice isomorphic to a Hilbert space in fact a Hilbert lattice?

The title says it all: Let $E$ be a Banach lattice, which is isomorphic to a Hilbert space (as normed spaces). Is there an equivalent Hilbert norm on $E$, which still makes it a Banach lattice with ...
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5 votes
1 answer
186 views

If a subspace $F$ is contained in a subspace $G$, and $H$ is close to $G$, can we choose a subspace of $H$ close to $F$?

Let $E$ be a Banach space. Recall that the collection of all closed linear subspaces of $E$ can be turned into a metric space in a number of ways. In particular, consider the notion of a gap: if $G$ ...
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5 votes
1 answer
226 views

A "proof" that all separately continuous maps on LF-spaces are continuous

Problem Consider the locally convex spaces $C^\infty(\mathbb{R})$ and $C^\infty_c(\mathbb{R})$, the former equipped with its standard Fréchet topology, the latter equipped with the inductive limit ...
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1 vote
0 answers
202 views

Complete topological groups in which all subgroups are closed

My previous question has been answered by YCor; so I am asking a new one with a reasonable additional assumption. See the previous question for the background and motivation. General question: does ...
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7 votes
1 answer
447 views

Topological groups in which all subgroups are closed

General question: does there exist a nondiscrete topological group $G$ such that all subgroups of $G$ are closed? Or, does there exist a nondiscrete topological vector space $V$ such that all vector ...
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5 votes
1 answer
262 views

Is the filtered colimit topology on the space of signed Radon measures linear and locally convex?

Let $X$ be a compact Hausdorff space. In chapter 3 of Peter Scholze's Lectures on Analytic Geometry he considers the space of signed Radon measures on $X$ equipped with the filtered colimit (aka ...
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