Skip to main content

All Questions

24 questions from the last 30 days
Filter by
Sorted by
Tagged with
14 votes
4 answers
2k views

The ten most fundamental topics in geometric group theory

What are the ten most fundamental topics in geometric group theory? This is a pedagogical question prompted by the fact that I am teaching geometric group theory to undergraduates. They are expected ...
5 votes
1 answer
735 views

Can the Pythagorean theorem be proved using imaginary numbers?

Can the Pythagorean theorem be proved using imaginary numbers? The proof must avoid circular reasoning, of course. I asked essentially the same question at MSE, but did not receive a definitive answer,...
Dan's user avatar
  • 3,577
1 vote
2 answers
225 views

Bounds of zeta function near $\Re(s)=1$

Richert proved in https://link.springer.com/article/10.1007/BF01399533 that $$ \zeta(s) =O\left( |\Im(s)|^{100(1-\Re(s))^{3/2}} (\log |\Im(s)|)^{2/3}\right)$$ uniformly in the region $\Re(s)\in [1/2,1]...
Dr. Pi's user avatar
  • 3,062
3 votes
2 answers
147 views

Vector bundles over a Stein space are projective

It is a "well known" fact that locally free sheaves over a Stein space $X$ are projective as $\mathcal{O}_X$-modules (see e.g. just after Lemma 1.6 in O'Brian-Toledo-Tong's "The trace ...
Tim's user avatar
  • 1,109
5 votes
1 answer
274 views

Why "no wandering domain" fails in parabolic basin?

Theorem (Sullivan). Every Fatou component $U$ of $f$ rational map is eventually periodic, that is, there exist $n > m > 0$ such that $f^n(U) = f^m(U)$ I am familiar with the proof: spread around ...
Ricky Simanjuntak's user avatar
-3 votes
1 answer
105 views

when does $h$ exist?

Let $\zeta(s)$ denote the Reimann zeta function in the critical strip. It is easy to see that $$ \zeta(s) = 0 \Longleftrightarrow \Re(\zeta(s))+\Im(\zeta(s)) = 0 ~~~~ \text{and} ~~~~~~ \Re(\zeta(s)) \...
Roy Burson's user avatar
2 votes
1 answer
201 views

Section 3 of Atiyah's "On analytic surfaces with double points" — some questions

I have some questions about section 3 of Atiyah's "On analytic surfaces with double points," a short 9 page paper. Section 3 is all dedicated to proving lemma 4. Near the end of section 3, ...
maxo's user avatar
  • 129
-3 votes
1 answer
195 views

Bounding a number-theoretic integral

Find a good upper bound on $$\int_1^T\frac{\zeta'(s)}{\zeta(s)\zeta(1-s)}X^sdt,$$ where $s=c+it$ for a constant $c>1$ and $X>0$ is a parameter. If needed, we can assume RH. My attempt here is ...
charlie_beck's user avatar
0 votes
1 answer
119 views

Nonstationary phase method for oscillatory integral

I want to approximate an integral of the form $$\int_a^bf(t)e^{ig(t)}dt,$$where $f(t)$ is smooth, $g(t)$ is real-valued and smooth. The stationary phase method says that if $t_0\in [a,b]$ is such that ...
charlie_beck's user avatar
12 votes
0 answers
122 views

When could a diligent calculus student compute all Picard iterates algebraically?

As is well known, in the typical proof of the Picard–Lindelöf theorem, one shows the existence of a solution of the initial value problem $y'(t) = f(t,y(t))$, $y(t_0) = y_0$ by considering the Picard ...
James E Hanson's user avatar
1 vote
1 answer
63 views

Need bound for absolute value of complex-valued special functions (Taylor coefficients of Faddeeva's w(z))

To guarantee accuracy for code [1] that computes Faddeeva's w(z) [2] using Taylor expansions around different centers, I would need upper bounds for the absolute values $|w_n(z)|$ of the coefficients $...
Joachim W's user avatar
  • 111
0 votes
0 answers
84 views

Singular behavior of zeros of incomplete zeta function

I've been looking at the zeros of the incomplete zeta function $\zeta_{lower}(s, z)$ recently. $$ \zeta_{\mathrm{lower}}(s,z)=-\frac{{\Gamma(1-s)}}{2\pi i}\int_{z}^{\infty}\frac{{(-t)^{s-1}}}{e^{t}-1}...
Zhobbyist's user avatar
0 votes
0 answers
79 views

Alternative proof of parabolic implosion

I am working on an alternative proof of parabolic implosion from complex dynamics, but only allowing hyperbolic perturbation. Theorem (Parabolic Implosion) Let $f(z)=z^2+z$ and $U_f$ be parabolic ...
Ricky Simanjuntak's user avatar
-5 votes
0 answers
86 views

Every smooth function contains a bijection [closed]

Let $f:\mathbb{D}\rightarrow \mathbb{R}$ be a continuous non-constant over $\mathbb{D}$. Is there always a subset $\mathbb{A}\subseteq \mathbb{D}$ such that $f:\mathbb{A}\rightarrow \mathbb{R}$ is a ...
John Wayne's user avatar
-4 votes
0 answers
65 views

Is the real and imaginary part of the Dirichlet eta function closest to its partial sums when trigonometric function changes signs? [closed]

To grasp the question we are concerned with three Theorems 1,2, and 3 in bold font below. First let us consider the Dirichlet eta function $\eta: \mathbb{C}\rightarrow \mathbb{R}$ $$ \eta(s) = \sum_{n=...
Roy Burson's user avatar
0 votes
1 answer
127 views

Holomorphic functions of certain blow up at origin

Suppose that $D=\{z\in \mathbb C\,:\, |z|\leq 1\}$ and let $f$ be holomorphic on $D\setminus\{0\}$ such that $|f(z)|\leq e^{\frac{1}{|z|}}$ for all $0<|z|\leq 1$ and assume additionally that $\lim\...
Ali's user avatar
  • 4,115
2 votes
0 answers
55 views

Closed form of $\frac{1}{{\pi}^n}\sum_{k\in \mathbb{Z}^n}\prod_{j=1}^n\frac{1}{1+(m_{j}^{T}k)^2}$

Given vectors $m_{j}\in\mathbb{Z}^{n},M=(m_{1} \ldots m_{n}),\det(M)\not =0$. Is it possible to find a closed form of: $$S=\frac{1}{{\pi}^n}\sum_{k\in \mathbb{Z}^n}\prod_{j=1}^n\frac{1}{1+(m_{j}^{T}k)^...
Quý Nhân's user avatar
1 vote
0 answers
53 views

Description of all biholomorphic maps from annulus [duplicate]

Consider the collection $\mathcal{C}$ of all maps $f \colon B_1 -\overline{B}_\beta \to \mathbb{C}$ such that $f$ is biholomorphic onto its image. Is this collection $\mathcal{C}$ path-connected? In ...
Jinyang wu's user avatar
1 vote
0 answers
148 views

integral over the unit sphere of $\Bbb C^n$

Please, is there a way to calculate this integral $$\int_{S_{2n-1}} \frac{e^{a \langle z, \zeta \rangle}}{|z - \zeta|^{\beta}} \, d\sigma(\zeta)$$ where $ z $ is a fixed point in the complex unit ball ...
zoran  Vicovic's user avatar
2 votes
0 answers
70 views

Is the hypothesis "uniformly equivalent" needed?

I am reading S. Shimorin's paper titled Complete Nevanlinna-Pick property of Dirichlet-type spaces. My question concerns Lemma 2.3. which is as follows: Assume $\mathscr{H}$ is a Hilbert space of ...
ash's user avatar
  • 151
0 votes
0 answers
57 views

Complexity of evaluation of analytic functions

Given an analytic function $f(x)$ (say as combination of elementary functions and operators), is it possible to compute $n$ first bits of the value of the function on the whole interval $[a, b]$ ...
roignoirewg's user avatar
1 vote
0 answers
53 views

Can one explicitly define a right inverse for a convolution operator on the space of entire functions?

A result of Meise and Taylor in 1988 shows that every non-zero convolution operator on the Frechet space $H(\mathbb{C})$ of all entire functions on $\mathbb{C}$ has a continuous linear right inverse $...
David Walmsley's user avatar
2 votes
0 answers
50 views

Convergence of finite-difference method for Cauchy-Riemann equations

Let $I\subseteq \mathbb{R}$ an open interval. Let $f:I\rightarrow \mathbb{C}$ real analytic. Suppose we want to numerically compute an analytic extension of $f$. We will assume the following: we are ...
Plemath's user avatar
  • 312
1 vote
0 answers
39 views

Currents with logarithmic poles compared with those with no poles

I am learning Deligne homology via U. Jannsen, "Deligne homology, Hodge-$\mathscr{D}$-conjecture, and motives." There, the currents with logarithmic poles are given in Definition 1.4 by $$ '\...
neander's user avatar
  • 161