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0
votes
0answers
29 views

Is it local diffeomorphism? [on hold]

Let $f : \mathbb{R}^n \to \mathbb{R}^n$ be a smooth function and let $x_{0}$ be a hyperbolic fixed point ($f(x_{0}) = x_{0}$). Is it true that $f$ is local diffeomorphism around $x_{0}$? From inverse ...
0
votes
0answers
30 views

Hardy-type inequality for point boundary

Let $f$ be in $W^{2,p}(\mathbb{R}^n)$ for $n\geq 3$ and $p>n/2$, with $f=0$ at the origin. I want to show that the integral $$\int_{B(0,r)} (f |x|^{-2})^p dV <\infty$$ for some small $r>0$. A ...
-3
votes
0answers
43 views

Question about Holder functions [on hold]

Let the definition of the oscillation about a point be given as $ \mathrm{osc}[f] (x) : = \lim\limits_{\epsilon \rightarrow 0} \sup_{[x -\epsilon, x + \epsilon]} f - \inf_{[x -\epsilon, x + ...
3
votes
0answers
59 views

“Integrating” solenoidal vector fields

Let $U$ be a bounded open subset of $\mathbb{R}^d$ with Lipschitz boundary, and $g \in L^2(U,\mathbb{R}^d)$ be a solenoidal vector field (i.e. $\nabla \cdot g = 0$). Then $g$ can be written in the ...
0
votes
0answers
27 views

Period doubling bifurcation curve [on hold]

Can I locally approximate the curve occurring at a fixed point where a period doubling bifurcation occurs? I think so as the f' != 1 at this point so by Implicit Function Theorem we should be able to ...
0
votes
0answers
66 views

Ask for a good reference for the calculus involving singular continuous measure [migrated]

I am not an expert on measure theory. I am sorry if this question is too simple for some experts here. Suppose the measure $\mu$ is singular continuous on $\mathbb{R}$, such as the cantor measure. ...
0
votes
1answer
227 views

For what measures $\mu$ does $\mu*f\in L^{\infty}$ where $f$ is a given continuous integrable function?

I am trying to characterize all measures on $\mathbb{R}$ such that $$ \sup_{x\in\mathbb{R}} \: (\mu*f)(x)<+\infty, $$ where $f(x)$ is some specific integrable functions, such as $f(x)=e^{-|x|}$, ...
0
votes
1answer
44 views

A function with one partial derivative Hölder continuos is Hölder continuos?

I'm having trouble finding a function of two variables, say $u(t,x)$, such that for some $\alpha\in ]0,1]$ 1. $(t,x)\mapsto \partial_x^2 u(t,x)$ is $C^{0,\alpha}$; 2. $(t,x)\mapsto \partial_x ...
0
votes
1answer
111 views

Is the span of those vectors dense in $\ell_2$?

For all $x \in \mathbb{R}^n$ and $\alpha \in \mathbb{Z}_{\geq 0}^n$ let $x^\alpha=x_1^{\alpha_1} \cdots x_n^{\alpha_n}$. Let $$\ell^2=\{z=(z_\alpha)_{\alpha \in \mathbb{Z}_{\geq 0}^n}:\, z_{\alpha} ...
0
votes
0answers
116 views

When is there a polynomial transformation? [on hold]

First part: given $$\frac{P_1(x_1,x_2,\dots,x_n)}{P_2(x_1,x_2,\dots,x_n)}=\frac{P_3(f(x_1,x_2,\dots,x_n))}{P_4(f(x_1,x_2,\dots,x_n))}|\det (J(f(x_1,x_2,\dots,x_n)))|$$ where $P_i$ is polynomial ( that ...
15
votes
1answer
485 views

Solving a non linear equation

I've been trying to prove that the following equation has a unique solution in interval 0 < x < 1 : $$ x = \Big(\frac{1 - (1-x^2)^K}{1 - (1-x)^K}\Big)^2 $$ Where K is a number (integer, if it ...
3
votes
1answer
378 views

the existence of a real polynomial satisfying the following property

It is easy to verify that $$ \frac{t}{2}\leq \frac{1}{4}+\frac{1}{4}t^2\leq \frac{t}{1-(1-t^2)^2}-\frac{t}{2} \quad \quad 0<t\leq1$$ I want to ask if there exist a real polynomial $h(t)$ such ...
2
votes
2answers
89 views

Question on the number of equilibria

Let $f: C \to C$ be a smooth function and $C$ be a compact set, subset of $\mathbb{R}^n$. We assume that all the fixed points are hyperbolic. Is it true that the number of fixed points is finite or ...
1
vote
1answer
54 views

Monotonicity of Trapezoid Approximations

Here's a numerical analysis question which may not be very important, especially in practice, but has been bugging me. Suppose $f$ is a continuous function on an interval $[a,b]$. Let $T_n(f)$ be ...
4
votes
3answers
331 views

Inequality of arithmetic, geometric and harmonic means

Let $a_1,\dots,a_n$ be positive numbers, does the following inequality holds? $$\frac{a_1+a_2+\cdots+a_n}{n}-\sqrt[n]{a_1a_2\cdots a_n}\geq\sqrt[n]{a_1a_2\cdots ...
2
votes
1answer
114 views

Inequality for the tail of normal distribution function

Let $ Ф(x) = \frac{1}{\sqrt{2\pi}} \int_{-\infty}^{x} e^{-t^2/2} \, dt $ be the cumulative distribution function of the standard normal distribution. Numerical calculations suggest the following ...
-1
votes
0answers
46 views

problem of integration by substitution [closed]

Hello everyone I have a question which is not of research level but I would like someone gives the related reference for this issue. Let $\mu:=\mu(dx)$ be a probability measure on $\mathbb{R}$ such ...
0
votes
0answers
53 views

Controlling the $C^\infty$ norm of a cutted off function on a smaller set [closed]

Good morning everybody. Let us work in $\mathbb R^n$ for simplicity and assume $K$ to be a compact subset. Let $B$ be a ball containing $K$ and let $f\in C^\infty(K)$. By the Whitney extension ...
-1
votes
0answers
48 views

Convergence of an integral containing the Fourier transform of compact supported function

Let $u\in {{L}^{1}}\left( \mathbb{R} \right)$, ${{\left\| u \right\|}_{{{L}^{1}}\left( \mathbb{R} \right)}}=1$, $u\ge 0$, $\operatorname{supp}\left( u \right)\subset \left[ -S,S \right]$. Here ...
0
votes
2answers
102 views

Can a monotone exponentially decreasing function be uniformely approximated bt Gaussians?

This question originates an engineering application. There is a certain process that is presumed to be a sequence of diffusions and is usually modelled as a sum of Gaussians: $$\Sigma_n ...
2
votes
1answer
168 views

Integration of gaussian times absolute value of cosine

Is there a way to compute/estimate the following integral? $\int_0^\infty e^{-(x/c)^2}\left|\cos{x}\right|dx$ where $c$ is a real constant. I would like to know if it is of order $e^{-c^2/4}$ like the ...
0
votes
1answer
49 views

Extending point-wise bound to uniform bound

Suppose $f(t,x)\in \mathcal{C}^0([0,1]\times \mathbb{R}^n)$. Further suppose that for each $t$ $$ C(t):= \sup_{x\in\mathbb{R}^n} |f(t,x)|<\infty \, .$$ Does it follow that $f$ is bounded? Note ...
3
votes
1answer
100 views

Separability of $R_+\times\mathcal{C}(R_+)$

Let $\mathcal{C}(R_+)$ be the space of continuous functions $f$ defined on $[0,+\infty)$ with $f(0)=0$. Denote by $\Omega$ the product of $R_+$ and $\mathcal{C}(R_+)$. Now endow $\Omega$ with the ...
4
votes
1answer
99 views

Are there superexponential Pfaffian functions?

This question is motivated by model theory, but it's really an analysis question (which means it may have an easy analysis answer that I just don't have the background for). Here's the main question, ...
4
votes
0answers
75 views

Strong convexity of the trace of the square root of a matrix function

Any clues about how to prove that the following function is strongly-concave in $x$? (We conjecture it is $2$-strongly concave but cannot prove it. We have already proved strict concavity through ...
6
votes
0answers
109 views

Interpolation between L^1 and Sobolev Space

Suppose $D^\alpha$ is fractional differentiation of order $\alpha$ on the real line. Is it true that $||D^\alpha f||_{L^\frac{2 \beta}{2 \beta - \alpha}({\mathbb R})} \leq C_{\alpha,\beta} ...
-1
votes
2answers
113 views

Is real analytic function good enough (see problem)? [closed]

Let $f \colon \mathbb{R}\to \mathbb{R}$ be real analytic and let $A\subseteq \mathbb{R}$ be such that the set $A'$ of all accomulation points od $A$ is not empty. If $f(a)=0$ for all $a \in A$ is then ...
0
votes
0answers
124 views

Does there exist this special kind of homeomorphism?

Let $A,B\subset\mathbb{R}^n, n\geq 2,$ are two different shaped spindles. One is thick and one is thin. (Sorry for my unprofessional statements. Unsure about how to say it rigorously.) So there are ...
0
votes
0answers
99 views

how to solve f(f(x))=x^2+x [duplicate]

Now I just know the equation f(f(x))=x^2+x, how can I find the f(x)? I have already tired many times,but I found it is difficult to solve it by any way I knew.So please help me solve the problem,and ...
3
votes
3answers
334 views

Non-zero smooth functions vanishing on a Cantor set

It is easy to give examples of continuous functions $f:[0,1]\to \mathbb R_+\cup\{0\}$ non-zero but vanishing on a Cantor set (ex: Can Cantor set be the zero set of a continuous function?). It is ...
0
votes
0answers
11 views

Hello, everyone, I want to ask you a question about a proof in the Terence Tao's Real Analysis notes [migrated]

everyone. I am using Terence Tao's Real Analysis notes to self learn Analysis 1. There is one thing in the proof of Theorem 27 (Least Upper Bound Property) in “week 2 note” that I don’t understand ...
3
votes
0answers
126 views

Inverse Function Theorem on Zygmund Spaces, is the inverse in the same Zygmund Space?

Preliminary Definition We define the Zygmund spaces $C^r_{*}$ with $r>0$, $r \in \mathbb{R}$ in the following way: (all the functions are allowed to have values in $\mathbb{R}^m$, via working with ...
6
votes
0answers
128 views

If the generating function summation and zeta regularized sum of a divergent exist, do they always coincide?

One could assign a value to divergent series by means of several summation methods. One summation method we could consider is the generating function method. Let's sum, for example, the fibonacci ...
0
votes
1answer
202 views

Prove that these two definitions of “natural” integration constant coincide when both converge

These are two possible definitions of antiderivative (integral) incorporating a supposedly natural choice of an integration constant (see this question for further details). The first one is based on ...
-2
votes
1answer
411 views

Why calculus textbooks do not include the natural integration constants in the tables of integrals? [closed]

The formulas for integrals in the textbooks usually define indefinite integral up to a constant term. Yet the natural integration constant for antiderivative can be fixed from the following formula ...
22
votes
8answers
1k views

Continuous relations?

What might it mean for a relation $R\subset X\times Y$ to be continuous? In topology, category theory or in analysis? Is it possible, canonical, useful? I have a vague idea of the possibility of ...
13
votes
4answers
534 views

Is the sequence of Apéry numbers a Stieltjes moment sequence?

Consider the sequence of Apéry numbers $$ A_n = \sum_{k=0}^n \binom{n}{k}\binom{n+k}{k}\sum_{j=0}^k \binom{k}{j}^3 = \sum_{k=0}^n \binom{n}{k}^2\binom{n+k}{k}^2 . $$ In an email, physicist Alan Sokal ...
0
votes
0answers
28 views

Integrating over the Intersection of Convex Regions

Is there a way to integrate over the intersection of a finite collection of convex regions, using only the definition of the regions (i.e. without actually calculating the intersections)? The ...
1
vote
2answers
196 views

Set of distinct real numbers such that all combination of sums are distinct

Let $\Lambda :=\{\lambda_1, \dots, \lambda_n\}$ be a set of $n$ distinct real numbers. For a given $p \in \mathbb N$, consider further the set $$I_p := \{ \{i_1, i_2, \dots, i_p\} : i_j \in \{1, ...
3
votes
1answer
138 views

Can't figure out “standard application” of the Garsia-Rodemich-Rumsey Lemma

I'm currently reading the paper http://arxiv.org/abs/0908.2473 and can't figure out what they call a "standard application" of the Garsia-Rodemich-Rumsey lemma (see p.8). Summed up, they have a ...
0
votes
0answers
61 views

what is the best estimation for the following

Suppose a continuous $2\pi$-periodic function $f:R\rightarrow R$ satisfies $$ |f(x+\delta)+f(x-\delta)-2f(x)|\leq \mathrm{const}\frac{\delta}{\Big(\log\frac{1}{\delta}\Big)^{\gamma}}, \,\,\, ...
4
votes
2answers
196 views

What is the status of the extreme value theorem in forms of constructive mathematics, such as Smooth Infinitesimal Analysis?

In certain intuitionistic frameworks the extreme value theorem cannot be proved. Depending on the exact framework, counterexamples can be constructed as well; see for example pp. 294-295 in ...
1
vote
0answers
72 views

Estimating convolutions of powers

I would like an asymptotic estimate of $$ \sum_{y \in \mathbb{Z}^d} \frac{1}{|y-a_1|^{d-1} \ldots |y-a_n|^{d-1}} $$ that does not involve any infinite summation. In order to lighten the notation, I ...
6
votes
1answer
162 views

Finiteness as a motivation for compactness

Another history question, and I am not sure if I will get any answers. (If anyone knows of a good history of math list to use for this question I would be happy for any tips. The one I used to post to ...
0
votes
1answer
56 views

Continuous real function on germs

Let $C_0^{m,n}$ be the space of germs of continuous maps from $\mathbb{R}^m$ to $\mathbb{R}^n$, located at $0\in\mathbb{R}^m$, with the usual inductive limit topology. One can also consider ...
4
votes
1answer
115 views

On a.e. approximate differentiability of certain continuous real functions

I have the following question: If $f:[0,1]\to \mathbb{R}$ is a bounded continuous function of $\sigma$-finite variation in sense 1, then is it true that $f$ is approximately differentiable a.e. on ...
2
votes
2answers
105 views

Name of a generalized version of semi-continuity

I have recently made use of the following generalization of a continuous function, which seems simple enough it ought to have been used before, but I cannot find any references. We will say a ...
6
votes
1answer
192 views

Spectrum of this ODE

I noticed something interesting studying this Sturm-Liouville Problem: $$ \frac{d}{dx}\left(\sqrt{(1-x^{2})}\frac{df}{dx} \right)+\frac{\left(n \alpha x+\alpha^2 x^{2} + ...
2
votes
1answer
191 views

Measure of the same set in different models of ZF

Let $A$ be a definable subset of $\mathbb{R}$ in $\mathsf{ZF}$, and let $\mathcal{M},\mathcal{N}\models\mathsf{ZF}$ such that $A$ is lebesgue measurable in both models. Is ...
2
votes
1answer
193 views

The class of uniformly accelerated curves and surfaces

Once upon a time I was travelling by train and noticed an intresting optic effect I started to think about in terms of math. Let's consider two examples of curves: 1)The curve defined by the ...