Questions tagged [inequalities]
for questions involving inequalities, upper and lower bounds.
1,654
questions
5
votes
1
answer
218
views
An inequality for polynomials
I have been thinking about the validity of the following inequality: if $P(z)=\sum_{k=0}^na_kz^k, a_n\neq 0$ and $P(z)$ is non-zero in $|z|<1, $ then for $\theta \in [0, 2\pi],$ and $p>0$
\...
3
votes
0
answers
98
views
Convex minorants to convex functions, given partial Taylor expansion and smoothness estimate
Let $V$ denote a strictly convex function (in arbitrary dimension) whose Hessian is $L$-Lipschitz. Given only this knowledge, and the values of $\left\{ V \left( x \right), \nabla V \left( x \right), \...
0
votes
0
answers
97
views
Polynomial / quadratic autonomous system of ODEs – proving monotonicity / convexity
Problem:
Consider the autonomous ODE system
\begin{align*}
\dot{x} &= (1-x) (z-xy)\\
\dot{y} &= \tfrac 1 2 y^2 - (a+xy)(1-y) \\
\dot{z} &= \tfrac 1 2 z^2 - \tfrac 1 2 y^2 + (a+xy)z
\end{...
3
votes
2
answers
232
views
Extend an inequality on matrix norms
Let $A$ denote an $n \times n$ matrix, and $\sigma_i(\cdot)$ denote $i$-th largest singular value. Can we extend the following result to general $p \geq 1$?
For all $k = 1, \dots, n$,
$$ \sum_{i = 1}^...
1
vote
1
answer
220
views
What does Landau symbol mean in an inequality?
I'm reading about subdifferentiable function at page 232 of Villani's Optimal Transport: Old and New.
Definition 10.5 (Subdifferentiability, superdifferentiability). Let $U$ be an open set of $\...
4
votes
0
answers
123
views
A "counterbalancing" trigonometric sum inequality
Is it true that
$$s_{n,k}:=\sum_{j=1}^{n-1} r_{n,k,j}
<0$$
for all natural $n\ge2$ and all natural $k\in\{1,\dots,n-1\}$,
where
$$\text{$r_{n,k,j}:=\frac{x_{n,2j}}{y_{n,k,j}\;y_{n,k+1,j}},\quad$
$...
2
votes
1
answer
740
views
Can we get that $ P(N^{2/3}(\lambda_N-\lambda_{N-1})\le c)\ge 1-\epsilon$?
Following this question: Can we apply the continuous mapping theorem for the limiting joint distribution of the Tracy-Widom law?.
We know that
$$
\lim_{N\to\infty}P(N^{2/3}(\lambda_N-2)\le s_1,\dotsc,...
1
vote
2
answers
179
views
What is the easiest way to prove the correctness of this inequality
I have the following inequality for some $0<x<0.1$: $$x^{1/10}-(1-(1-x)^{x^{-0.5}}) \geq 0$$
Is there an easy way to prove the correctness of such inequality? Thanks!
0
votes
1
answer
84
views
Can we find the following $k$ so that the following inequality holds for asymptotic normal?
Following this question:Can we find such $k$ so that the following inequality holds?.
Consider a sequence of independent $n-$dimensional random vectors $u, v_1, v_2,\dots, v_k$ uniformly distributed ...
3
votes
0
answers
40
views
Bound of a regular function that cancels at some points
Let $K$ be a bounded convex set of $\mathbb{R}^n$ and $x_1,\ldots,x_k\in K$. Let $f: \mathbb{R}^n \rightarrow \mathbb{R}$ be a $C^\infty$ function that cancels on points $x_1,\ldots,x_k$ . When $n=1$, ...
2
votes
3
answers
213
views
Can we find such $k$ so that the following inequality holds?
I found this question: Chernoff style concentration bound for ratio of variables.
I want to ask if we get similar thing for the ratio of the sum and the one Gaussian variable.
Given i.i.d. Gaussian ...
2
votes
1
answer
132
views
Normalized concentration inequality for empirical CDF (iid sum)
Consider the empirical and population CDF,
$$
F_n(t) = \frac{1}{n} \sum_{i=1}^n 1\{X_i \leq t\} \quad \mbox{and} \quad
F(t) = \mathbb{E} [F_n(t)],
$$
where above $X_1, \dots, X_n$ are iid, real-...
0
votes
0
answers
33
views
Inequalities for generalized variance
Let $(X, \mu)$ be a measured space with $\mu(X) = 1$.
Given $\phi \in L^\infty(X, \mu)$, $\phi > 0$, let me define, for $\alpha \geq 1$, $\beta > 0$, the quantity
$$
I(\alpha, \beta) = \left(\...
4
votes
1
answer
146
views
An algebraic inequality in three real variables
Is it true that
$$(v-u)^2+(w-u)^2+(w-v)^2 \\
+\left(\sqrt{\frac{1+u^2}{1+v^2}}
+\sqrt{\frac{1+v^2}{1+u^2}}\right) (w-u)(w-v) \\
-\left(\sqrt{\frac{1+u^2}{1+w^2}}+\sqrt{\frac{1+w^2}{1+u^2}}\right) (w-...
9
votes
2
answers
573
views
Integral inequality: Prove $\int_0^1 f\int_0^1 1/f \leq 1$ for a certain function $f$
Let $g$ be a piecewise smooth, zero average, function over $[0,1]$ such that $\min g^2>0$. I would like to show that
$$
\int_0^1 g\sqrt{1-r/g^2}\int_0^1 \frac{1}{g\sqrt{1-r/g^2}} \leq 1
$$
for all $...
10
votes
1
answer
457
views
For what kind of $C^*$ algebras does the inequality $\frac{(ab+ba)}{2}\leq\frac{ a^p}{p} +\frac{b^q }{q}$ hold for $a,b>0$?
Assume that $\frac{1}{p}+\frac{1}{q}=1$ for two positive real numbers $p,q$.
For what kind of $C^*$ algebras $A$ does the following hold:
$$\frac{ab+ba}{2}\leq \frac{a^p}{p}+\frac{b^q}{q}$$ $\...
0
votes
0
answers
238
views
Can we prove the following anti-concentration inequality of polynomials of square Gaussian variables?
Following this question Anti-concentration of Gaussian quadratic form. We have the following inequality:
Let $X_1,\dots,X_n$ denote i.i.d. standard Gaussian random variables. For every $\epsilon>0$...
4
votes
0
answers
141
views
Approximation by gaussian mollification in Sobolev spaces
I have been trying to find a good estimate on the constant in the inequality (in dimension $d=3$ to simplify)
$$\label{0}\tag{0}
\|(1-e^{t\Delta})f\|_{L^{5/3}(\Bbb R^3)} \leq C_0\,t^{2/5}\, \|\nabla \...
4
votes
0
answers
122
views
Log of a truncated binomial
Let $X$ follow a binomial distribution with $n$ trials and success probability $p$, and let $0\leq k\leq n$. Are there any natural approximations or bounds for the ratio $$\frac{\boldsymbol{E}\log\...
6
votes
3
answers
919
views
Proof of a matrix implication
If $A = \begin{bmatrix} x & 1\\ y & 0\end{bmatrix}, B = \begin{bmatrix} z & 1\\ w & 0\end{bmatrix}$, for $x,y,z,w \in \Bbb{R}$.
I have observed by considering many examples of $x,y,z,...
5
votes
1
answer
148
views
On existence of a concave function
Let $a$ be a strictly positive $C^\infty$ smooth function on the unit interval. Does there exist a strictly positive $C^\infty$ smooth function $f$ on $I$ such that
$$ f’’(x) \leq 0\quad \text{and} \...
4
votes
1
answer
331
views
Inequality with decreasing rearrangement function
Let $f^{*}$ be the usual decreasing rearrangement function of a measurable function $f$ on a measure space $(X, \mu)$. Let $1<p<n$ and set $$p'=\frac{pn}{n-p}.$$ Also, let $g$ be a positive ...
0
votes
2
answers
427
views
How to prove that $1/ ((y+z) x^4) + 1/ ((z+x) y^4) + 1/ ((x+y) z^4) \geq 3/2$ for $x, y, z>0$ such that $xyz=1$? [closed]
How to prove that $\dfrac{1}{(y+z) x^4} + \dfrac{1}{(x+z) y^4} + \dfrac{1}{(y+x) z^4}\geq3/2$ for $x, y, z>0$, such that $xyz=1$?
9
votes
2
answers
611
views
How was Claim 5 in "A non-linear generalisation of the Loomis–Whitney inequality and applications" thought up?
In Bennett, Carbery and Wright's paper A non-linear generalisation of the Loomis–Whitney inequality and applications, Claim 5 was used to generalise the case from characteristic functions to simple ...
1
vote
1
answer
108
views
Finding an analytical upper bound on linear transform of matrix
Given a (real) positive semi-definite matrix $\underline M$ (with all elements of the principal diagonal equal to $1$) and a transformation $T:\underline A\to \underline A + \alpha \underline D$, with ...
6
votes
1
answer
447
views
a problem in complex-variable inequality
Let $n\ge2$ be a given positive integer, and $z_{1},z_{2},\cdots,z_{n}\in \mathbb{C}$,such
$$|z_{1}|^2+|z_{2}|^2+\cdots+|z_{n}|^2\ge n.$$
Prove or disprove
$$f_{n}=\sum_{j=1}^{n}\left|\sum_{I\subseteq ...
1
vote
1
answer
67
views
Lower bound $L_{1}$-metric with $L_{2}$-metric for bounded pdfs, on common support
Setup
To clarify, let constants $0 < a < b < \infty$, and $p \in \mathbb{N}$ be fixed. Further let $B \subset \mathbb{R}^{p}$ be a fixed compact support. We then define the space of bounded (...
2
votes
2
answers
183
views
Elementary convexity example
I'm trying to check that certain examples of Young functions in the harmonic analysis literature are actually Young functions, and in doing so need to prove the following convexity-like inequality for ...
7
votes
2
answers
453
views
An elementary inequality of operators
Suppose $a,b$ are two positive-definite linear operators on (say) $\mathbb R^n$. For $p\in(0,1)$, do we then have $(a+b)^p\leq a^p+b^p$ (with respect to the Loewner order)?
2
votes
0
answers
238
views
Largest eigenvalue of a Laplacian matrix to lower bound the prime counting function?
Let $L_n$ be the Laplacian matrix of the undirected graph $G_n = (V_n, E_n)$ (which is defined here: Why is this bipartite graph a partial cube, if it is? ) with sorted spectrum:
$$\lambda_1 (G_n) \ge ...
1
vote
1
answer
264
views
An inequality involving the Wasserstein distance and chi-squared distance
$\newcommand{\N}{\mathbb N}$Let $P$ be the set of all probability mass functions on $\N_0:=\{0\}\cup\N$, where $\N:=\{1,2,\dots\}$. Let $P_{>0}$ denote the set of all $q=(q_0,q_1,\dots)\in P$ such ...
1
vote
0
answers
67
views
Shapiro inequality for divisor sets
The Shapiro inequality is the statement that if $x_1, x_2, \dots, x_n$ are positive, with $x_{n+1}=x_1, x_{n+2}=x_2$, then $$\sum_{i=1}^{n} \frac{x_i}{x_{i+1}+x_{i+2}} \geq \frac{n}{2}.$$ This can be ...
4
votes
1
answer
302
views
When does the sine transform result in a positive function?
For each $x>0$ is, $$\int_0^\infty \tanh(t)e^{-\cosh(t)} \sin(x t) dt > 0\ \ \ ?$$
In general, it is known that if the kernel is decreasing, then the sine transform is positive. Note that this ...
6
votes
2
answers
578
views
Doubts in first lemma in the paper of Adams regarding sharp Moser inequality
This question is on a point in D.R. Adams paper "A Sharp Inequality of J. Moser for Higher Order Derivatives". Precisely the lemma says:
Given $a(s,t)$ be a non negative measureable function ...
0
votes
1
answer
91
views
Is set of integer solutions to these inequalities finite?
Consider the inequalities
$$\frac{(2A-1)^2}{4A^2}xy\leq \Big(\frac{x+y}2\Big)^2\leq\frac{(2A-1)^2}{4(A-1)^2}xy$$
$$x,y\geq0$$ where $A>10^9$.
Is the set of integer solutions to $x,y$ finite?
2
votes
1
answer
218
views
On the infimal convolution of two norms on $\mathbb R^n$
$\newcommand{\R}{\mathbb R}$For natural $n$, $a\in\R^n$, and real $t>0$, let
\begin{equation*}
K:=K_{n,t}(a):=\inf_{x\in\R^n}(\|a-x\|_2+t\|x\|_1),
\end{equation*}
\begin{equation*}
M:=M_{n,...
7
votes
2
answers
353
views
On a von Bahr–Esseen-type inequality for pairwise independent zero-mean random variables
For $p\in(1,2)$, let $C_p$ be the smallest constant factor $C$ in the von Bahr–Esseen-type inequality
\begin{equation}\label{eq:pair}\tag{1}
E\Bigl\lvert\sum_{j=1}^n X_j\Bigr\rvert^p\le C\sum_{j=1}...
3
votes
2
answers
242
views
Inequality for Gaussian polynomials III
Recall the constructions $[n]_q=\frac{1-q^n}{1-q}, [n]!_q=[1]_q[2]_q\cdots[n]_q$ with $[0]!_q:=1$ and the $q$-binomials (Gaussian polynomials)
$$\binom{n}k_q=\frac{[n]!_q}{[k]!_q[n-k]!_q}.$$
Given two ...
5
votes
1
answer
235
views
Maximal inequality of iid random variables $\{X_{ij}\}_{1\leqslant i,j \leqslant n}$
Suppose that $\{X_{ij}\}_{1\leqslant i,j\leqslant n}$ are iid random variables with $\mathbb{E}(X_{11})=0$ and $\mathrm{Var}(X_{11})=1$, does the following convergence hold:
$$
\max_{1\leqslant j\...
1
vote
1
answer
54
views
Can the second-order difference control the first-order difference for nowhere differentiable functions?
Suppose that $f$ is a continuous, nonconstant function on $[0,1]$. Fix some $0<a<1$. Is it possible to establish the following inequality
$$ |f(x+h)-f(x)| \leq C \left[ |h|^a + |2f(x)-f(x+h)-f(x-...
1
vote
0
answers
184
views
Schatten norm inequality
Let $A,B$ be two $n\times n$ matrices.
Find a lower bound of the $p$-th Schatten norm
$\|(A-B)(A-B)^\ast\|_{S_{p/2}}^{1/2}$ in terms of Schatten norm of $\|(AA^*+BB^*)\|_{S_q}$ for any relation ...
5
votes
0
answers
238
views
Equality from the Grothendieck inequality
I asked the following question on math.stackexchange.com but have not received any response. So I would like to try my luck here.
This question is related to the Grothendieck inequality. Let field $\...
1
vote
1
answer
142
views
Proof of lower bound on variance
I'm reading through the paper Poincaré type and spectral gap inequalities with fractional Laplacians on Hamming cube.
However, I'm having a difficult time understanding the following proof: Lemma 2.1 ...
3
votes
1
answer
142
views
Bounds on symmetric polynomials in power-sum form with bounded coefficients
Let $\boldsymbol{x}=(x_1,\ldots,x_n)$ be a real vector. Define the normalized power-sum symmetric polynomials by $\pi_j(\boldsymbol{x})=\frac 1n(x_1^j+\cdots+x_n^j)$.
For a partition $\lambda= (j_1,\...
-1
votes
1
answer
95
views
A proof of an interesting inequality [closed]
If $0<\beta<1$ and $0<x<1,$ how to prove that $$h(x)-2x+(4-2^{1+\beta})x^{1+\beta}<0,$$ where $$h(x)=(1+x)^{1+\beta}-x^{1+\beta}-1.$$The numerical simulation shows that it is true.
2
votes
0
answers
80
views
Inequality on polynomials
Recall $[n]_q=\frac{1-q^n}{1-q}, [n]!_q=[1]_q[2]_q\cdots[n]_q$ and the Gaussian polynomial $\binom{a}{b}_q=\frac{[a]!_q}{[b]!_q[a-b]!_q}$ with $[0]!_q:=1$.
Given two polynomials $U(q)=\sum_k\alpha_kq^...
1
vote
1
answer
97
views
Size of sets associated to Gaussian integers
Given a non-zero Gaussian integer $z$, we define the set $\mathcal S(z)$
containing all solutions
of $ab+cd=z$ satisfying $\min(\vert a\vert,\vert b\vert)>\max(\vert c\vert,\vert d\vert)$ with $a,b,...
4
votes
1
answer
164
views
Estimate an improper integral
Suppose that $f$ satisfies $a$-Hölder condition on $[0,1]$ ($0<a<1$). Fix $0<b<a$. For any $x\in [0,1]$ and sufficiently small $\delta>0$, is the following inequality established?
$$ \...
2
votes
1
answer
73
views
An inequality about the second-order difference
Fix a continuously differentiable but nowhere twice differentiable function $f$ on $\mathbb{R}$ supported on $[0,1]$. Is it true that for all $x\in[0,1]$ and all $\delta$ sufficiently small
\begin{...
0
votes
0
answers
67
views
Gagliardo-Nirenberg type inequality for fractional relativistic Laplacian operator?
In [1], authors note that by the seminal approach of M. Weinstein in [2] and [3], there is a non-trivial solution $Q\in H^s(\mathbb{R})$ which optimizes next Gagliardo-Nirenberg type inequality:
$$\...