# Questions tagged [limits-and-convergence]

Convergence of series, sequences and functions and different modes of convergence.

430
questions

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33 views

### Proof of limits of sequences tending to infinity [closed]

How can we prove this :
Prove that if $\quad$ $\lim_{n\to+\infty} y_n$ = $\lim_{x\to+\infty} z_n$=$+\infty$
then $\quad$ $\lim_{n\to+\infty} v_n$ = $\lim_{x\to+\infty} w_n$=$+\infty$ .
With $w_n=\...

**6**

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**0**answers

100 views

### Let $a(n) = a(\pi(n)) + a(n-\pi(n))$ with $a(1) = a(2) = 1$. What is $\lim_{n\to \infty} \frac{a(n)}{n}$?

My question is related to https://oeis.org/A316434. Let
$$a(n) = a(\pi(n)) + a(n-\pi(n))$$ with
$a(1) = a(2) = 1$, where $\pi(n)$ is the prime-counting function. Does the following limit exist?
$$\...

**-1**

votes

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56 views

### Can we say that $ \frac{1}{n}\sum_{i=1}^{n}{f_i(t)\to 0 }~\text{a.e} $ [closed]

Let $(E,\mathcal {A},\mu)$ be a finite measure space and $\{f_n\}$ be a sequence bounded in $L^1$, such that:
$$
f_n(t)\to 0 ~~\text{a.e and in } L^1
$$
Can we say that
$$
\frac{1}{n}\sum_{i=1}^{n}{...

**0**

votes

**1**answer

80 views

### Finding a connection between two types of convergence

Please, help me find connections between two types of convergence:
Let $\{X_n\}_{n\ge1}: (\Omega,F,P) \rightarrow (\mathbb{R},Bor)$ be a sequence of r.v., there are two convergences:
1) $X_n \...

**0**

votes

**1**answer

45 views

### Limit of the convolution of derivative of Gaussian heat kernel

I'm looking for the following limit:
$$\lim_{\varepsilon\to 0^+}\int_{-\sqrt{\varepsilon}}^{\sqrt{\varepsilon}}\frac{1}{\sqrt{2\pi}\varepsilon^{3/2}}\left(-1+\frac{x^2}{\varepsilon}\right)e^{-\frac{x^...

**0**

votes

**1**answer

115 views

### Spherical harmonics expansion

In the context of $L^2$ space, it is usually stated that any square-integrable function can be expanded as a linear combination of Spherical Harmonics:
$$
f(\theta,\varphi)=\sum_{\ell=0}^\infty \sum_{...

**0**

votes

**1**answer

77 views

### Analyze a complicated double summation

Let $f(x)$ be a real-valued twice continuously differentiable function, and considered the below double sum $$F(t,f(x)):=\dfrac{1}{t}\Big(\sum_{k=0}^{\infty}\sum_{m=0}^{\infty}f(x+(k-m)/\sqrt{n})\...

**1**

vote

**1**answer

62 views

### The weak convergence of finite dimensional distribution of Gaussian process does not imply the weak convergence in $C[0,1]$

In the study of weak convergence in $C[0,1]$, a common example is always being considered: $$X_{n}(t)=nt1_{[0,1/n]}(t)+(2-nt)1_{(1/n,2/n]}(t).$$ This example serves a counter-example to show that the ...

**0**

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**0**answers

25 views

### Finding the upper bound and uniform convergence

For every positive integer $m$, let $x_0^{(m)}$ < $x_1^{(m)}$ < ... < $x_m^{(m)}$ be $(m+1)$ distinct points in $[0, \pi]$ and let $p_m$ $\in$ $P_{m+2}$ be the Hermite interpolant of the ...

**0**

votes

**1**answer

149 views

### Properties of Dirichlet series

I have a question about convergence and properties of Dirichlet series. it seems a bit interesting and different about the convergences of Dirichlet Series to me.
With $c\in [0,1]$,
$$f(n) = \pm 1,...

**-2**

votes

**1**answer

422 views

### Prove or disprove this integral of a function, defined on a countable set with infinite limit points, converges to zero [closed]

Edit: I got rid of my old definitions. Everything should be clear now
Since no one has answered my question on MSE, I’m hoping to get an answer here. I apologize if you dislike my writing. I am an ...

**-2**

votes

**1**answer

147 views

### Convergence in $C_c$ but not in $C$

Let $C_c(\mathbb{R})$ be the set of compactly-supported continuous functions on $\mathbb{R}$. We can view this with a number of different topologies but I have my eye on two in particular. Let $X$ ...

**1**

vote

**1**answer

68 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 $X_N$.

**2**

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**0**answers

30 views

### Characterization of uniformly convergent sequence of functions

Let $f_n$ a sequence of continuos function from a metric space $(X,d)$ itself. If $f_n$ converge uniformly to a function $f $ and $\varphi$ is real valued uniformly continuos function defined on $X$...

**2**

votes

**1**answer

38 views

### Countable convergence-determining class for weak convergence of probability measures

Suppose that $E$ is a Polish space.
Portmanteau theorem asserts that a sequence $(\mu_n)$ of Borel probability measures weakly converges to a Borel probability measure $\mu$ (shortly, $\mu_n\overset{...

**0**

votes

**0**answers

48 views

### if $\max_{z \in K} |\zeta(z+it)-f(z)|<\epsilon.$ then is this $\lim_{t\to \infty} \inf \frac {|\zeta'(z+it)|}{|f'(z)|} $ a finit limit?

Universality theorem of Riemann zeta function states that :Let $K$ be a compact subset with connected complement lying in the strip $\{1/2 < \operatorname{Re}(z)<1\}$, and let $f : K \rightarrow ...

**2**

votes

**1**answer

69 views

### Convergence of semi convex functions

Definition. Let $u:\Omega \rightarrow \mathbb{R} $. A function $u$ is called semiconvex if $u=v+w$ for some $v\in C^{1,1}(\Omega)$ and a convex function $w$.
Note. Saying that $u$ is semiconvex is ...

**4**

votes

**2**answers

192 views

### $| f_n |^p - | f |^p - | f_n-f |^p$ converges in distribution sense if $f_k$ converges almost everywhere and weakly to $f$?

Let $1<p<\infty$ and $f_n$ be a sequence in $L^p(S^1)$ that converges weakly to some $f$. Here $S^1$ is the circle so we are dealing with periodic functions.
Let us see if $| f_n |^p - | f |^p -...

**0**

votes

**1**answer

48 views

### Connected graphs $G$ with $\delta(G) > 1$ and long minimum size roundtrips

Let $G = (V,E)$ be a finite, connected, simple, undirected graph. By a roundtrip of $G$ we mean a map $r:\{0,\ldots,n\} \to V$ for some $n\in\mathbb{N}$ with the following properties:
$r$ is ...

**2**

votes

**1**answer

87 views

### Convergence of estimator given by a fixed point

Let $X$ be a non-negative random variable with cdf $F$ and define
$$G(s) = E[\max(0,u(X)-sX)],$$ where $u$ is some real function.
Let $s_0$ be the unique fixed point of $G$.
Now let $X_1,\dots,X_t$ ...

**2**

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**0**answers

55 views

### Convergence of Bayesian posterior

Let $\Delta [0,1]$ denote the set of all probability distributions on the unit interval.
Let $\mu \in \Delta [0,1]$ denote an arbitrary prior. Importantly, $\mu$ does not necessarily admit a density ...

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64 views

### If $u_n \to u$ in $H^1_0(\Omega)$, does $\chi_{\{u_n = 0\}} \to g$ for some $g$ in some space, for a subsequence?

Let $\Omega$ be a bounded and smooth domain.
Suppose we have $u_n \to u$ in $H^1_0(\Omega)$. We know that for a subsequence, $\chi_{\{u_n = 0\}} \rightharpoonup f$ to some $f$, weak-* in $L^\infty(\...

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50 views

### About generalized binomial theorem and Grünwald-Letnikov fractional derivative

I have run into a problem while computing the fractional derivatives of order $\alpha$ for the Riemann zeta function. My Theorem states
Let $s\in\mathbb{C}$, $\mathfrak{Re}(s)>1$, then the ...

**5**

votes

**2**answers

463 views

### Geometry of Level sets of elliptic polynomials in two real variables

Updated:
A polynomial $P(x,y)\in \mathbb{R}[x,y]$ is called an elliptic polynomial if its last homogeneous part does not vanish on $\mathbb{R}^2\setminus\{0\}$.The two answers to this post provide ...

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37 views

### Tightness of a uniformly bounded sequence of functions integrated with respect to a semimartingale

I am reading this paper by Jacod, Jakubowski and Mémin. In the proof of Theorem 1.3 the authors define, for each $n\geq1$ the function $\phi_n$ by
$\quad\phi_n(s)=i+1-ns,\quad\text{if } \frac{i}{n}&...

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88 views

### Is this integral finite and how does it decay to zero?

I would like to know if the following is convergent/finite (it represents a bound from a truncated Legendre series approximation)
\begin{equation}
\varepsilon_n \leq \int_{-1}^1 \left(\int_{n\gg 1}^\...

**1**

vote

**1**answer

89 views

### Weak-* convergence in $L^\infty((0,T)\times\Omega)$ implies weak-* convergence in $L^\infty(\Omega)$ for a.e. $t \in (0,T)$?

Let $\Omega$ be a bounded and smooth domain. Suppose I have a sequence of non-negative functions $u_n \in L^\infty((0,1)\times \Omega) \cap L^\infty((0,1);L^\infty(\Omega))$ with
$$0 \leq u_n \leq 1 \...

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43 views

### A ballot-casting problem

For any set $X$ and cardinal $\kappa$ let $[X]^\kappa$ denote the collection of subsets of $X$ with cardinality $\kappa$. If $n$ is a positive integer, let $[n]:=\{1,\ldots,n\}$.
Let $V$ and $K$ be ...

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**2**answers

557 views

### What does the abbreviation “p.p.” mean in the context of convergence [closed]

What does the abbreviation "p.p." mean when referring to convergence? E.g. in the following paper by Harry Pollard
THEOREM. If $f \in L^p$ for some $p$ in the range $\tfrac{4}{3} <p < \infty$,...

**5**

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75 views

### $L^p$-convergence of truncated Legendre series approximation to inverse error function $\text{erfinv}$

Bounding the $L^p$-error for an $n$-th order Legendre series approximation
I have function $f\,\colon (-1, 1) \to \mathbb{R}$ where $f \in L^q(-1, 1)$ for any $q \geq 1$. I approximate $f$ using a ...

**0**

votes

**1**answer

93 views

### Matrix iteration for non-negative matrices. Does it converge to some eigenvector?

Let $A$ be a non-negative (entrywise) matrix such that $A(1,1)>0$. Set $u=(1,0,0,...,0)^T$. Is it always true that there exists a non-negative eigenvector $v$ of $A$ such that $\lim_{n\rightarrow\...

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53 views

### Density of integers related to the size of its order of appearance in the Fibonacci sequence

Let $z(n)=\min\{k>0 : n\mid F_k\}$. This function is known as the Fibonacci entry point (for example). A result of Sallé gives the sharpest upper bound for $z(n)$, namely, $z(n)\leq 2n$, for all $n$...

**1**

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73 views

### Reference for the positive probability of convergence to a stable point of a stochastic approximation algorithm

Consider a stochastic approximation process with
$$x_{t+1} = x_t + \frac{1}{t} (g(x_t)+u_t)$$
where $(u_s)_s$ is a sequence of i.i.d. shocks.
Assume $g$ is Lipschitz, $u_t$ has finite variance, and ...

**5**

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**0**answers

78 views

### Intuition behind the local limit theorem in hyperbolic groups

Let $\Gamma$ be a finitely generated group and let $\mu$ be a probability measure on $\Gamma$. Denote by $X_n$ the induced random walk. Finally, let $p_n=\mu^{*n}(e)=P_e(X_n=e)$. The local limit ...

**4**

votes

**1**answer

286 views

### About $a_n = \frac{a_{n-1}(a_{n-1} + C)}{a_{n-2}}.$

Let $A,B,C > 0$. Put $a_1 = A$ and $a_2 = B$ and, for integer $n > 2$,
$$a_n = \frac{a_{n-1}(a_{n-1} + C)}{a_{n-2}}$$
and
$$ T = \lim_{k \to \infty} \frac{a_k}{ a_{k - 1}}.$$
Notice the limit ...

**-1**

votes

**1**answer

61 views

### Closed on generic set implies closed set whole set [closed]

Assume that $f:\mathbb{R}^{2}\rightarrow \mathbb{R}^{2}$ is a continuous on a set $A$. Let $B \subset A$ be a generic set in $\mathbb{R}^{2}$ i.e, the countable intersection of the open and dense ...

**7**

votes

**1**answer

181 views

### Graphons and Graphs

The situation is as follows: assume we have a sequence of simple weighted graphs $(G_n)_{n\in\Bbb{N}}$. For the terminology that follows I refer to Limits of dense graph sequences by László Lovász and ...

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**0**answers

104 views

### Convergence in unbounded domains

Lemma. Let $\mu$ be a measure in $\mathcal{M}(\Omega)$ and let $(v_{n})$ be a sequence of functions in $W^{1,p}_{0}(\Omega)\cap L^{\infty}(\Omega)$ converging to a function $v$ in the weak topology of ...

**1**

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87 views

### Uniform convergence over compacts subsets implies existence of a uiform convergente subsequence?

Let $H$ the group of all homeomorphisms of a locally compact second countable and totally bounded metric space $X$ onto itself, under the compact-open topology ($X$ is totally bounded if every ...

**3**

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72 views

### Arzela-Ascoli-analogue statement over a given cardinality of discrete space

(I think there would be better title for my question. If there is a good idea on the title, please let me know.)
Consider the following statement:
Let $A$ be a set (with the discrete topology, if ...

**3**

votes

**1**answer

110 views

### Order statistic - Rate of convergence of a p-quantile to the expectation

Fix some $k\in\mathbb N$ and some probability $p\in[0,1]$. Denote with $F_n$ the cdf of the k-th highest oder statistic (i.e. the distribution of the k-th highest draw) of $n$ draws from a uniform ...

**1**

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**1**answer

94 views

### Radius of convergence of multivariate Taylor series

Consider the function $f$ on $\mathbb{R}^{l}$ given by \begin{eqnarray}\left(x_{1},...,x_{l}\right)\mapsto\left(\sum_{i=1}^{l}\frac{1}{\left(1+x_{i}\right)^{k_{i}}}-\left(l-1\right)\right)^{-1} \end{...

**0**

votes

**1**answer

167 views

### Is this sum uniformly convergent? (MathStack question mistakenly posted here :I Apologies) [closed]

Is the $\sum_{n=1}^\infty \frac{nx}{1+n^3x^2} $ uniformly convergent on $(0,\infty)$?
Each individual term attains a max of $\frac{1}{2n^{1/2}} $ at $x=\frac{1}{n^{1.5}}$.
Notice that the maximizers ...

**1**

vote

**2**answers

265 views

### Generalized limits

Cross-posted from Math SE.
The linked question explores the concept of a "generalized limit" that assigns values to sequences which diverge in the Cauchy sense. It asks the following question:
...

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**0**answers

64 views

### Does $L^1$ convergence preserve the regularity of this sequence of functions?

Let $f_n$ be a sequence of $L^1(]0,1[)$ functions such that $f_n$ is non-decreasing, at least left-continuous, $f_n(0^+) <0$, $f_n(1^-) >0$, for all $n \in \mathbb N$. This sequence converges
$...

**-1**

votes

**1**answer

120 views

### Convergence in the narrow topology of measures and strongly converge for signed measures

We say that a sequence $(\mu_{n})$ of measures in $M_{b}(Q)$ converges tightly (or, equivalently, in the narrow topology of measures) to a measure $\mu$ in $M_{b}(Q)$ if
$$\lim_{n\to\infty}\int_{Q}\...

**4**

votes

**1**answer

168 views

### Counterexample to uniform convergence of Laplace series (expansion in spherical harmonics)

Expansion of a real function on 2-sphere in spherical harmonics, so-called Laplace series, converges uniformly for continuously differentiable functions (see e.g. https://projecteuclid.org/euclid.bbms/...

**5**

votes

**1**answer

310 views

### Convergence of the series of Legendre polynomials

Consider the generating function of Legendre polynomials:
$$\frac{1}{\sqrt{1 - 2xt + t^2}} = \sum\limits^{\infty}_{n=0} P_n(x)t^n$$
Is it true that for $0<x<1, t=1$ series of Legendre ...

**3**

votes

**0**answers

151 views

### Dominated convergence Theorem

I am struggling to understand the proof in the paper, Learning Temporal Evolution of Spatial Dependence with
Generalized Spatiotemporal Gaussian Process Models.
Theorem 2.1 in the page 33 uses ...

**1**

vote

**1**answer

102 views

### A problem inspired in the definition of tau numbers and a divisibility relationship related to powers of two

It is (I assume that this easy fact is well-known) obvious that an integer $n>1$ is a power of two $n=2^{\alpha}$, where $\alpha\geq 1$ is integer, if an only if $n$ satisfies the divisibility ...