All Questions
13,927 questions
0
votes
1
answer
137
views
Lower semi-continuity of induced function on sequences
Let $f:X\rightarrow [0,\infty)$ be (resp. weakly) lower semi-continuous on the reflexive Banach space $X$. Let $\ell^p(X)$ denote the space of $p$-summable sequences in $X$, i.e.: $\sum_{n=1}^{\infty}...
- 5,405
0
votes
1
answer
212
views
Expressing the measure of a set in terms of the characteristic function of the measure
Let $\mu$ be a discrete, finitely supported probability measure in $\mathbb{R}^d$ and denote by $\phi$ be the characteristic function of $\mu$, i.e. $\phi(t)=\mathbb{E}e^{i<t,X>}$, where $X$ is ...
- 2,288
0
votes
1
answer
86
views
Are bounded sets in second duals of locally convex spaces weak* pre-compact?
Let $X$ be a locally convex Hausdorff space. Then $X$ injects into $X^{**}$ via the canonical map $\kappa: X\to X^{**}$. Now, $X^{**}$ carries the weak* topology. Let $B$ be a bounded set in $X$. Is $\...
- 1
0
votes
1
answer
86
views
Kolmogorov entropy of a subset of $L^1$
How can we estimate the Kolmogorov $\epsilon$-entropy
$$H_\epsilon (A,L^1(\mathbb R))$$
where
$
A = \{f:\mathbb R \to [0,K] \text{ s.t. $f \in L^1$ and has total variation $TV(f) \le M$}\}
$?
- 839
0
votes
1
answer
188
views
a question about vector valued Banach spaces
I wonder the difference between $L^1(\mu\times\nu)$ and $L^1(\mu;L^1(\nu))$, as if partial derivatives can be exchanged with integration in the second spaces in many articles. In Folland's real ...
- 71
0
votes
1
answer
81
views
Ultrabornological representation for the space of uniformly continuous functions?
Let $\{\omega_i\}_{i\in I}$ be a non-empty set of increasing (not necessarily strictly) continuous functions preserving $0$. Then, for each $i \in I$ define the space
$$
C_{\omega_i}(\mathbb{R}^n,\...
- 5,405
0
votes
1
answer
734
views
Infinite composition of continuous functions
Let $f_n:\mathbb{R}\rightarrow \mathbb{R}$ be a sequence of functions and define $F_n:= f_n\circ \dots\circ f_1$. Then $F_n$ is continuous. However, the pointwise limit need not be (consider Mateusz'...
- 5,405
0
votes
2
answers
140
views
The derivative of a $C_0$-semigroup with respect to a perturbation parameter
Let $H$ be a Hilbert space, and $A : H \to H$ be the (semi-bounded) generator of the $1$-parameter $C_0$-semigroup $[0, \infty) \ni t \mapsto \mathrm e ^{-t A}$. Let $B : H \to H$ be a bounded ...
- 5,407
0
votes
1
answer
126
views
Extensions of trace class operators
Let $H_i, K_i$ for $i=1,2,3$ be Hilbert spaces with horizontal exact sequences. Assume $T_1, T_2, T_3$ have dense range, that $T_1, T_2, T_3$ are trace class operators and that the squares commute. ...
- 1,338
0
votes
1
answer
380
views
How to solve the integral equation $f(x)=\frac{\lambda\int_{x}^1 \sqrt{1+(f(t))^2}dt+c_1}{\int_{x}^1 \sqrt{1+(f(t))^2}dt+c_2}$?
Recently, I have asked a question about variational analysis (First moments of uniform distribution on a curve from (0,0) to (1,1) in two-space). Such the question can be addressed in some cases by ...
- 550
0
votes
1
answer
178
views
Convergence in LB-spaces
Edit:
Let $X$ be a strict LB-space described by $\lim X_n$ and suppose that $\{x_n\}_{n \in \mathbb{N}}$ converges in $X$. I'm looking for a reference showing that $x_n$ must converge in some $X_N$.
- 5,405
0
votes
1
answer
345
views
$L^p$ norm inequalities with respect to strongly-log-concave densities
Let $\pi(x)=\frac{e^{-f(x)}}{\int_{\mathbb{R}^d}e^{-f(u)}du}$ be a strongly-log-concave distribution, i.e., $f(x):\mathbb{R}^d\rightarrow R$ is an $m$-strongly convex function. Also, $f(x)$ has $L$-...
- 9
0
votes
1
answer
76
views
Friedrich's extension of the generator of a continuous time markov chaoin
Consider the infinitesimal generator $G$ of a Markov chain with state space $\mathbb{Z}$ such that it is symmetric with respect to a measure $\mu$ on $\mathbb{Z}$. Then, the operator $(G,C_c(\mathbb{Z}...
- 407
0
votes
1
answer
233
views
Existence of subsequences convergence with weak topology
Let $\left\{ {{\varphi _n}} \right\}$ is the sequence bounded in ${L^\infty }\left( {0,\infty ;H_0^1\left( {0,1} \right)} \right)$. Is there exists $\varphi \in {L^\infty }\left( {0,\infty ;H_0^1\...
- 183
0
votes
2
answers
776
views
A question about homogeneous distribution
A distribution in $\mathscr{S}^{\prime}\left(\mathbb{R}^{n}\right)$ is called homogeneous of degree $\gamma \in \mathbb{C}$ if for all $\lambda>0$ and for all $\varphi \in \mathscr{S}\left(\mathbb{...
- 11
0
votes
1
answer
102
views
Law of a step function and its generalization to two dimensions on an appropriate spaces
Let's consider two discontinuous functions defined on $D$ and $D \times [0,T]$, respectively:
A step function: $u_1(x)=\begin{cases}
u_{L}, x<c_1, \\[2ex]
u_{R}, x>c_1,
\end{cases}$
A "...
- 657
0
votes
1
answer
360
views
Fractional Sobolev norm of characteristic function of an interval?
Is there an explicit expression giving a fractional Sobolev norm of the characteristic function of some interval $I=[a,b)$?
I believe it is true that $\chi_{I} \in W^{s,1}(\mathbb{R})$ for $s < \...
0
votes
2
answers
210
views
Limited sum for whole sum approximation
Let $d_n, n\in\{1,2,\cdots,N\}$ be $N$ realizations drawn independent and identically from uniform distribution on $(0,L)$ where $L=\gamma\sqrt{N}$ with constant $\gamma$. Suppose that we need to ...
- 287
0
votes
1
answer
153
views
On tensor products of (essentially) bounded measurable functions
Let $F:\mathbb R^2\rightarrow\mathbb R$ be an essentially bounded measurable function ($\mathbb R^d$ is equipped with its standard Lebesgue measure) and assume that
$F(x,y)=F(y,x)$. I would like to ...
- 16.2k
0
votes
2
answers
403
views
Application of uniform boundedness principle
$\DeclareMathOperator\Lip{Lip}$Let $\Lip_0(\mathbb R^d)$ be the space of Lipschitz functions $f:\mathbb R^d\to\mathbb R$ vanishing at zero, i.e., $f(0)=0$, and equipped with the norm $\|f\|:=\|\nabla ...
user128095
0
votes
1
answer
159
views
Bisector Projection
Let $p,q$ be two projections of a $C^*$ algebra. A projection $l$ is called a bisector projection to $(p,q)$ if $$|pl-l|=|ql-l|$$ The motivation comes from the geometric intuition of "...
- 366
0
votes
1
answer
65
views
Is there a general guideline for minimizing $\sup_{y\in H}F(\;\cdot\;,y)$?
Let $H$ be a $\mathbb R$-Hilbert space and $F:H^2\to\mathbb R$. Is there a general guideline for minimizing $\sup_{y\in H}F(\;\cdot\;,y)$?
Since the question is rather abstract, feel free to impose ...
- 167
0
votes
1
answer
136
views
A link between continuity and 0-borelian? [closed]
Is it true that :
1/ if $f$ real continuous and $O$ an open set then $f(O)$ is a 0-borelian?
2/ if $A$ a 0-borelian set then there exists $f$ real continuous and $O$ an open set with $A=f(O)$?
$B$ ...
- 4,074
0
votes
1
answer
72
views
Equality between two norms on $\mathcal{L}(E)^n$
Let $E$ be a complex Hilbert space and $\mathcal{L}(E)$ the algebra of all bounded linear operators on $E$.
On $\mathcal{L}(E)^n$, we have two equivalent norms:
\begin{eqnarray*}
N_1({\bf A})
&=&...
- 1,154
0
votes
1
answer
352
views
Weak continuity under Laplace transform
Let the sequence $u_n\in L^2(0,\infty)$ weakly converges to $u\in L^2(0,\infty)$. What can we say about the corresponding Laplace transforms $U_n(s)$ and $U(s)$?
$U_n(s)$ converges point-wise to $U(s)...
- 395
0
votes
1
answer
111
views
If a topological space (X,T) is completely normal, and if we double the point of X, is the resulting space also completely normal? [closed]
I have a question on my proof of the following lemma, and I'd like to know if my answer is correct.
Lemma. Suppose $(X,T)$ is any completely normal topological space. Let's double the points of $X$, ...
- 73
0
votes
1
answer
91
views
Topologically transitive dynamical system mapping space into ball
Let $X$ be a separable Hausdorff topological space and $\phi \in C(X,X)$ be a topologically transitive map. Further, let $V$ be a fixed non-empty open subset of $X$. Then does there necessarily ...
- 5,405
0
votes
1
answer
124
views
"Geometric" Decomposition of Wiener Space
Let $C_0([0,1];\mathbb{R}^d)$ be the classical Wiener space (of continuous paths with initial value $0$) and let $\nu$ be the Wiener measure on this space. Does there exist a countable family $\left\{...
- 5,405
0
votes
1
answer
223
views
Dense $G_{\delta}$ set with $\sigma$-porous complement is cofinite?
Let $X$ be a separable Banach space and $D\subseteq X$ be a
proper, connected, and dense $G_{\delta}$ subset of $X$,
$X-D$ is $\sigma$-porous.
Then is $X-D$ contained in a finite-dimensional ...
- 5,405
0
votes
1
answer
211
views
Relationship between a certain binary optimal transport and total-variation of modified distributions
Let $\mathcal X$ be a Polish space, and let $(N_x)_{x \in \mathcal X}$ be a system of closed neighborhoods in $\mathcal X$. Define $\Omega := \{(x,x') \in \mathcal X^2 \mid N_x \cap N_{x'} = \emptyset\...
- 6,853
0
votes
1
answer
204
views
A certain class of representations
Let $g$ be a non-identity element in a torsion-free amenable group, does there exist a finite-dimensional unitary representation $\pi$ with $\pi(g)\neq 1$?
(The word "finite-dimensional" was ...
- 2,118
0
votes
1
answer
582
views
$L^2$ bound and interpolation of Hölder norm
Consider the function
$$F(x):=\int_{\mathbb R} f(t+x)f(t-x) \ dt .$$
Clearly, we have by Cauchy-Schwarz
$$\vert F(x) \vert\le \Vert f \Vert^2_{L^2} $$
$$\vert F'(x)\vert\le 2\Vert f' \Vert_{L^2} \...
user144765
0
votes
1
answer
134
views
Lower semicontinuity of a multi-valued map $F:X\to 2^Y$ in term of net
Let $X,Y$ be two Hausdorff spaces and $F:X\to 2^Y$ be a multi-valued mapping. We says that $F$ is lower semicontinuous at $x_0\in X$ if for each $y_0\in F(x_0)$ and any neighborhood $U\in \mathcal N(...
- 1,245
0
votes
2
answers
254
views
Proving that preorder on the set of measurable functions is symmetric
Let's say I have specific preorder $\prec$ on set $S$ and I want to prove that in fact it is equivalence relation. What is known already:
$S$ is set of measurable functions $f : \Omega \rightarrow X$ ...
- 105
0
votes
1
answer
183
views
Sufficient and necessary condition for the global uniqueness of fix-points
https://www.ams.org/journals/proc/1976-060-01/S0002-9939-1976-0423137-6/S0002-9939-1976-0423137-6.pdf
This paper gives a sufficient condition for the uniqueness of SCHAUDER fix point. I wonder if ...
- 263
0
votes
1
answer
60
views
Empty interior lack of minima
Suppose that $U \subseteq \mathbb{R}^d$, and satsifies
$U$ is dense in $\mathbb{R}^d$,
U has empty interior,
Then is it possible that
$$
\inf_{x \in U} f(x) >\inf_{x \in \mathbb{R}^d} f(x),
$$
...
- 5,405
0
votes
1
answer
151
views
$B _{\ell ^{2}} ^{+}$ with the norm $\lVert\lvert \cdot \rvert\rVert _{\sqrt{2}}$ doesn't have normal structure
$\newcommand\binorm[1]{\lVert#1\rVert}\newcommand\trinorm[1]{\lVert\lvert#1\rvert\rVert}$Consider the space $\ell ^{2}$ with the standard norm
\begin{align*}
\binorm x_{2} = \left( \sum _{i =1} ^{\...
- 23
0
votes
1
answer
226
views
Transformation of Fourier Transform
Suppose that $f$ is a function with a Fourier transform, and that $g:\mathbb{R}\rightarrow \mathbb{R}$ is a smooth function such that $g\circ f$ has a Fourier transform also.
Is there an expression ...
- 5,405
0
votes
1
answer
136
views
A question on existence of a Sobolev Hilbert space, where convergence implies uniform convergence [closed]
Is there a Sobolev Hilbert space $H^k(\Omega)$($\Omega$ open subset of $\mathbb{R}^m$, with a smooth boundary), for some $k \in \mathbb{N}$, such that, any sequence in the space $C^0(\bar{\Omega})\cap ...
- 698
0
votes
1
answer
115
views
Does there exists an extreme point $(a_1^*,...,a_n^*)$ of $B_{\mu^*}$ such that $a_i^*\neq 0$ for all $1\leq i\leq n$ and $\sum_{I=1}^n a_i^*a_i=1?$
Fix a natural number $n\geq 1.$
Let $\mu$ be a norm on $\mathbb{R}^n$ satisfying
$$\mu(0,...,0,\stackrel{i}{1},0,...,0) = 1 \quad\text{for all }1\leq i\leq n.$$
Let
$$B_{\mu} = \{(a_1,...,a_n)\in \...
- 623
0
votes
1
answer
75
views
Existence of certain subsemigroups of $C(K, K)$ for compact Hausdorff spaces $K$
Let $K$ be a compact Hausdorff space. I'm wondering: Does there always exist a subset $J \subseteq C(K, K)$ such that:
$J$ is closed under composition,
there is an element $f \in C(K)$ such that the ...
- 741
0
votes
1
answer
175
views
Accessible reference for (scattering) $\Psi DO$'s on manifolds
I am currently trying to understand Hassell, Tao, and Wunsch's paper on Strichartz estimates on non-trapping asymptotically conic manifolds, however, my understanding of pseudodifferential operators ...
- 1,247
0
votes
1
answer
88
views
Finite pre-images implies (local) branch cover?
Let $M_{1},M_{2}$ be (possibly non-compact) 2-dimensional, connected, smooth, orientable manifolds of finite topological type. Suppose you have smooth, surjective map $F:M_{1} \rightarrow M_{2}$, and ...
- 6,995
0
votes
1
answer
181
views
Does asymptotic behavior guarantee uniqueness?
Suppose $w$ is a solution of
$$\frac{d^2}{dx^2}w+\{u(x)+k^2\}w=0$$
with asymptotic condition
$$\lim_{x\rightarrow \infty}w(x)e^{ikx}=1$$
and $u\in L^1_1(\mathbb{R})=\{f:\int_\mathbb{R}(1+|x|)|f|dx<...
- 145
0
votes
1
answer
187
views
Harmonicity of the Martin kernels
Let $\Gamma$ be a finitely generated group and let $\mu$ be a probability measure on $\Gamma$. Consider the Green function $G(x,y)=\sum_{n\geq 0}\mu^{*n}(x^{-1}y)$, where $\mu^{*n}$ is the $n$th ...
- 2,090
0
votes
1
answer
386
views
Functions satisfying Neumann boundary condition
I have a question about functions satisfying a condition.
Let $D \subset \mathbb{R}^d$ be a Lipschitz domain. That is, for each $x \in \partial D$, there exists an open neighborhood $U$ of $x$ in $\...
- 721
0
votes
1
answer
185
views
Borsuk–Ulam theorem on the sphere with expluded poles [closed]
Consider a sphere without two poles $U^2$. Will Borsuk–Ulam theorem still work, i.e. $\forall$ continuous functions $f:U^2 \rightarrow \mathbb{R}^2 ~\exists x \in U^2$ such as $f(-x)=f(x)$?
- 415
0
votes
1
answer
170
views
About the topological center of a Banach algebra
Let $\mathfrak A$ be a Banach algebra with a bounded approximate identity (BAI), and let $\square$ and $\lozenge$ denote, resp., the first and the second Arens products of $\mathfrak A''$. Consider ...
- 2,118
0
votes
1
answer
365
views
Convergence of absolutely continuous probability measures
I have a sequence of absolutely continuous probability measures $\mu_{n}$ with finite second moment (ie. $\mu_{n}\in P_{ac}(\mathbb{R})\cap P_{2}(\mathbb{R})$), with densities $\rho_{n}\in L^{\infty}(\...
- 119
0
votes
1
answer
61
views
Is the difference between polyfits for two data series equivalent to the polyfit of the difference between the two data series?
Suppose that we have two series of data points $a(x)$ and $b(x)$ with the same domain of definition for $x$, and we fit two polynomial functions $f(x)$ and $h(x)$ (of the same order $n$) to them, ...
- 147