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

1 vote
Accepted

Limit laws for random matrix products covergence

Theorem 1.1 does not refer to a probabilistic limit, it holds elementwise for any given series of matrices that satisfies the conditions stated in the theorem.
Carlo Beenakker's user avatar
1 vote

What is the limit of this integral as $n$ approaches infinity for integer $k\geq 0$ and real...

$$I_{k,m}(n)=\int_{0}^{1}u^k\cot\left({\frac{\pi(1-u)}{m}}\right)\sin\left({\frac{2\pi n(1-u)}{m}}\right)\,du$$ $$\lim_{n\rightarrow\infty} I_{k,m}(n)=\frac{1}{2}m, \;\;\text{for}\;\; m\geq 1\;\; \te …
Carlo Beenakker's user avatar
10 votes

Value of $c$ such that $\lim_{n\rightarrow\infty}\sum_{k=1}^{n-1}\frac{1}{(n-k)c+\log(n!)-\l...

UPDATE I tried to evaluate the sum numerically for large $n$ and what I find does not support the conclusion I give below, that the large-$n$ limit equals 1 independent of $c$. Here is a plot for $c= …
Carlo Beenakker's user avatar
2 votes
Accepted

Limit of a hypergeometric function(1F2)

The large-$x$ limit is only zero if $a+b>3/2$: $$_1{F}_2({1}; {a, b}; -x^2/4)=$$ $$=\sqrt{\tfrac{1}{\pi}}\Gamma (a) \Gamma (b) \sin \left(\tfrac{\pi}{2} (a+b-\tfrac{1}{2})-x\right)(2/x)^{a+b-3/2}+{\ …
Carlo Beenakker's user avatar
4 votes
Accepted

Proof of a zeta function limit

Use the expansion $$\zeta(s)=\frac{1}{s-1}+\gamma+{\cal O}(s-1),$$ hence, since $\zeta(x)=1+2^{-x}+3^{-x}+4^{-x}+5^{-x}+\cdots$, you have $$\zeta(\zeta(x))=\frac{2^x}{1+(2/3)^x+(2/4)^x+(2/5)^x+\cdots} …
Carlo Beenakker's user avatar
6 votes

Asymptotic forms of Legendre functions for large degree

A series with precise error estimates is derived in Error bounds for a uniform asymptotic expansion of the Legendre function: $$P_n(\cosh x)=\left(\frac{x}{\sinh x}\right)^{1/2}\sum_{\nu=0}^{\infty}c …
Carlo Beenakker's user avatar
7 votes

Limit of recursion relation

Mathematica can actually solve the recursion relation in closed form, $$F_n(n)=-\tfrac{1}{2}(n^2-1)^{-1}\left(\frac{n-1}{n}\right)^n\left[n \left(\frac{n}{n-1}\right)^n \Phi \left(\frac{n}{n-1},1,n+1\ …
Carlo Beenakker's user avatar
2 votes
Accepted

Infinite limit of sums of gamma functions is constant?

For each $k>0$, $c\in\mathbb{C}$ it holds that $$\lim_{\alpha\rightarrow\infty}\frac{\Gamma(\alpha+c)}{\Gamma(\alpha)\alpha^c}=1\Rightarrow\lim_{\alpha\rightarrow\infty} \left(\log\frac{\Gamma(k\alpha …
Carlo Beenakker's user avatar
9 votes
Accepted

Solving a limit about sum of series

The sum $\sum _{n=0}^{\infty}t^{n^2}$ evaluates for $t<1$ to an elliptic theta function, and then taking the limit $t\rightarrow 1$ from below gives $$\lim_{t\nearrow 1}\sqrt{1-t}\sum _{n=0}^{\infty}t …
Carlo Beenakker's user avatar
4 votes
Accepted

Rate of convergence of Fejer kernel to the Dirac delta function

For any $\delta,x$ such that $0<\delta\leq |x|<\pi$ one has $|F_N(x)|\leq[2\pi(N+1)\sin^2(\delta/2)]^{-1}$, so the error in the delta-function approximation is of order $1/N$. Two explicit examples, i …
Carlo Beenakker's user avatar
5 votes

Asymptotic behavior of the "Cauchy square" series

You can reduce the evaluation of $S_n$ to a quadrature by means of the Abel-Plana formula, $$S_n=\sum _{s=1}^{n-1} g(s)=\int_1^{n-1}g(s)\,ds+\tfrac{1}{2}g(1)+\tfrac{1}{2}g(n-1)$$ $$\qquad\qquad -\,2\o …
Carlo Beenakker's user avatar
12 votes
Accepted

"Find $\lim_{n \to \infty}\frac{x_n}{\sqrt{n}}$ where $x_{n+1}=x_n+\frac{n}{x_1+x_2+\cdots+x...

The OP asks where this recursion relation might appear in a research context. It appears as a discretization of the Emden–Fowler nonlinear differential equation, $$f''(t)=t^{p}[f(t)]^q,$$ for $p=1$, $ …
Carlo Beenakker's user avatar
2 votes

Nature of $ \sum_{n \geq 1} \frac{ \cos(n) \sin(n+1) }{n} $

You might try to regularize the sum, $$S(\alpha)=\sum_{n=1}^\infty \frac{ \cos(\alpha n) \sin(n+1) }{n}= -\tfrac{1}{4} i \left[e^{-i} \ln \left(1-e^{i (\alpha-1)}\right)+e^{-i} \ln \left(1-e^{-i (\alp …
Carlo Beenakker's user avatar
2 votes

The limitation of derivation of modified Bessel function of second kind

Since $K_0(a\sqrt{x})\rightarrow-\frac{1}{2}\ln x-\gamma_{\rm Euler}+\ln(2/a)$ for small $x$, one has $$\lim_{x\rightarrow 0}\; (x\ln^2 x)\frac{\partial }{{\partial x}}\frac{{{K_0}(a\sqrt x )}}{{{K_0} …
Carlo Beenakker's user avatar
5 votes

Estimate on gaussian distribution

A general approach to obtain upper and lower bounds on $P(|X_1|\leq M_1, |X_2|\leq M_2,\dots, |X_d|\leq M_d)$ for a singular multivariate Gaussian, with a noninvertible covariance matrix, is developed …
Carlo Beenakker's user avatar

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