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Banach spaces, function spaces, real functions, integral transforms, theory of distributions, measure theory.

2 votes
1 answer
269 views

Decompose a function into a bounded part and a Lipschitz part

Let $f: \mathbb R^d \to \mathbb R^d$ be a measurable function such that $$ \sup_{x,y \in \mathbb R^d} \frac{|f(x) - f(y)|}{\max \{1, |x-y| \}} < \infty. $$ Are there functions $g,h: \mathbb R^d \to \ …
Akira's user avatar
  • 825
0 votes
1 answer
107 views

If $H \in L_{q} (\mu, X^*)$ such that $\int \langle H, f \rangle \mathrm d \mu = 0$ for all ...

I'm reading Theorem 1 at page 98 of Vector Measures by Joseph Diestel, John Jerry Uhl. Here we use the Bochner integral. Theorem 1 Let $(\Omega, \Sigma, \mu)$ be a $\sigma$-finite measure space, $1 \ …
Akira's user avatar
  • 825
0 votes
1 answer
277 views

Does $L_{p}(\mu, X)^*=L_{q} (\mu, X^*)$ hold for $\sigma$-finite measure spaces?

I'm reading Theorem 1 at page 98 of Vector Measures by Joseph Diestel, John Jerry Uhl. THEOREM 1. Let $(\Omega, \Sigma, \mu)$ be a finite measure space, $1 \leq p<\infty$, and $X$ be a Banach space. …
Akira's user avatar
  • 825
1 vote
Accepted

Does $L_{p}(\mu, X)^*=L_{q} (\mu, X^*)$ hold for $\sigma$-finite measure spaces?

Below is my formalization of @Nik's hints to finish the proof. Let's prove that $$ \sum_{m=1}^M \|H_m\|^q_{L_{p}(\mu_m, X)^*} \le \|H\|^q_{L_{p}(\mu, X)^*} \quad \forall M \in \mathbb N^*. $$ Let $\O …
Akira's user avatar
  • 825
2 votes
0 answers
78 views

Does this variant coincide with the usual Hölder space?

$\newcommand{\NN}{\mathbb N} \newcommand{\RR}{\mathbb R}$ Let $\alpha \in (0, 1]$ and $d, j \in \NN^*$. The usual Hölder space $C^{j, \alpha} := C^{j,\alpha} (\RR^d; \RR)$ is defined as the space of …
Akira's user avatar
  • 825
0 votes
1 answer
227 views

Is the space $L^p_{\text{loc}} (\mathbb R^d)$ separable w.r.t. the norm $\|f\|_{\tilde L^p} ...

Fix $p \in [1, \infty)$. Let $(L^p (\mathbb R^d), \|\cdot\|_{L^p})$ be the Lesbesgue space of $p$-integrable real-valued functions on $\mathbb R^d$. Let ${\tilde L}^p (\mathbb R^d)$ be the space of Le …
Akira's user avatar
  • 825
1 vote
2 answers
188 views

Does a measurable $F :[0, T] \to L^p (\mathbb R^d; \mathbb R_{\ge 0})$ have a "flattened" me...

Let $d \in \mathbb N^*,p \in [1, \infty]$ and $T>0$. Let $$ F :[0, T] \to L^p (\mathbb R^d; \mathbb R_{\ge 0}), t \mapsto F_t $$ be measurable. I would like to ask if there is a measurable function $G …
Akira's user avatar
  • 825
0 votes

Does a measurable $F :[0, T] \to L^p (\mathbb R^d; \mathbb R_{\ge 0})$ have a "flattened" me...

Below we use Bochner measurability and Bochner integral. Let $(X, \mathcal A, \mu)$ and $(Y, \mathcal B, \nu)$ be complete $\sigma$-finite measure spaces, $(E, | \cdot |)$ a Banach space, $S (X)$ the …
Akira's user avatar
  • 825
0 votes
1 answer
214 views

If we don't care about uniqueness, can we relax the coercivity condition in Lax-Milgram theo...

Let $(H, \langle \cdot, \cdot \rangle)$ be a real Hilbert space and $\|\cdot \|$ its induced norm. Let $a: H \times H \to \mathbb R$ be a bilinear form. We say that $a$ is coercive IFF there is $C>0$ …
Akira's user avatar
  • 825
1 vote
1 answer
86 views

Is it true that $\xi \in \partial G (v)$ implies $\frac{\xi}{F'(\phi (v))} \in \partial \phi...

I am reading the introduction of Chapter 10 in the book Gradient Flows by Ambrosio and his coauthors. As we have seen in Section 1.4, in the classical theory of subdifferential calculus for proper, l …
Akira's user avatar
  • 825
0 votes
1 answer
157 views

For $\mu$-a.e. $x \in X$, the sequence $(f_n(x, \cdot))_n$ is Cauchy in $L^1 (Y)$. Then $(f_...

Below we use Bochner measurability and Bochner integral. Let $(X, \mathcal A, \mu)$ and $(Y, \mathcal B, \nu)$ be complete $\sigma$-finite measure spaces, $(E, | \cdot |)$ a Banach space, $S (X)$ the …
Akira's user avatar
  • 825
1 vote
1 answer
89 views

Does an isometric automorphism of $L_p (X,\mu, E)$ preserve pointwise convergence?

Let $(X, \mathcal A, \mu)$ be a $\sigma$-finite measure space and $(E, |\cdot|)$ a Banach space. Here we use the Bochner integral. Let $p \in [1, \infty)$ and $q \in (1, \infty]$ such that $p^{-1}+q^{ …
Akira's user avatar
  • 825
0 votes
Accepted

Is there a modification of $f$ on a null set such that $F: [0, T] \to L^p ({\mathbb R}^d), t...

Let $(X, \mathcal A, \mu)$ and $(Y, \mathcal B, \nu)$ be complete $\sigma$-finite measure spaces, and $(E, | \cdot |)$ a Banach space. $S (X)$ the space of $\mu$-simple functions from $X$ to $E$. $\m …
Akira's user avatar
  • 825
0 votes
2 answers
124 views

Is there a modification of $f$ on a null set such that $F: [0, T] \to L^p ({\mathbb R}^d), t...

Let $T>0$ and $p \in [1, \infty)$. Let $f \in L^p ([0, T] \times {\mathbb R}^d)$. By a theorem in this thread, there is a Lebesgue null subset $N$ of $[0, T]$ such that $f(t, \cdot)$ is Lebesgue measu …
Akira's user avatar
  • 825
0 votes

Is there a modification of $f$ on a null set such that $F: [0, T] \to L^p ({\mathbb R}^d), t...

Inspired by two answers in this thread, I'm able to drop the assumption on the integrability of $f$, i.e., Theorem Let $p \in [1, \infty)$ and $f \in L^0 (Z)$ such that $$ f(x, \cdot) \in L^p(Y) \qua …
Akira's user avatar
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