2
votes
0answers
53 views

Normal-like coordinates for weakly differentiable metrics

Let $(M,g)$ be a Riemannian $W^{2,p}$ metric, with $p>n/2$. Thus $g$ is at least continuous. At any point $P\in M$, do there exist local coordinates $x^i$ such that $g$ can be decomposed as $g_{ij} ...
4
votes
0answers
107 views

What is a stable $(n,1)$-category?

My question in its simplest form is whether we have any understanding of stable $(n,1)$-categories, by analogy with stable $(\infty,1)$-categories and abelian categories (the latter being like "stable ...
1
vote
1answer
67 views

Entropy on a draw from a random distribution.

Suppose I am attempting to calculate the entropy of a continuous, normally distributed random variable $X$, from the distribution $\mathcal{N}(\mu, \sigma)$. This is easy to to do - I just calculate ...
3
votes
1answer
219 views

Theorem 7b of Serre's “Propriétés galoisiennes des points d'ordre fini des courbes elliptiques”

Could someone please point me towards a proof of the statement in the second paragraph, in the proof of Theorem 7b of Serre's Propriétés galoisiennes...? The statement is as follows: Let $F$ and $F'$ ...
0
votes
0answers
54 views

A normal form theorem for presentations of finite $p$-groups of nilpotency class $2$?

When constructing examples of nonabelian finite $p$-groups with abelian automorphism group (and certain other desired properties), the authors of papers like http://arxiv.org/pdf/1304.1974v1.pdf leave ...
0
votes
0answers
41 views

characterizing a sigma field generated by a field [on hold]

Given that $\mathcal{F}$ is a field (but not a $\sigma$-field), is there any characterization we can give of $\sigma(\mathcal{F})$, where $\sigma(\cdot)$ is the generating $\sigma$-field of a ...
7
votes
3answers
498 views

Is it consistent with ZFC (or ZF) that every definable family of sets has at least one definable member?

I consider definability to mean one of either cases: Definability without parameters (in the language of set theory), or Definability from ordinals and a real (in the same language). So my ...
0
votes
1answer
107 views

sum over primes involving divisor function (variation of the Titchmarsh divisor problem)

This question was also asked on MSE. Does there exist an asymptotic estimate for the following sum over primes $$ \sum_{p\leq x} \frac{\tau(p-1)}{p}\;, $$ where $\tau(n)=\sum_{d|n}1$ is the divisor ...
2
votes
0answers
214 views

Periodicity with irrational numbers [migrated]

Recently, I invented the following theorem and found a proof, it seems strange since it is very counter-intuitive to me. The proof is long and non-conceptual. Is there a place or a branch of math ...
1
vote
0answers
73 views

Simply-connected 4-manifolds can be blown up and down to complex projective planes. How about non-simply-connected ones?

There is a nice theorem that for every simply connected, closed, smooth, oriented manifold $M$, we have for some $m \in \mathbb{N}$: $$M \# \left(\mathop{\#}^m \left(\mathbb{C}\mathbb{P}^2 \# ...
0
votes
0answers
74 views

About the Intersection of the nested sequence of Chebyshev centers of weakly compact convex sets

Let $K_0$ be a weakly compact convex subset of a Banach space $X$. For each $n\in\mathbb{N}$, let $K_n$ be the set of Chebyshev centers of the set $K_{n-1}$. Suppose $K_0$ has a normal structure. Is ...
0
votes
0answers
40 views

Integration by parts for multidimensional Lebesgue-Stieltjes Integrals

I am concerned with the following problem: I am wondering if there exists any sort of integration by parts formula for a multidimensional Lebesgue-Stieltjes integral. In my case the integral is given ...
0
votes
0answers
28 views

Numerical analysis- Runge Kutta [on hold]

i have: y'(x)= sin(y); y(0)=1 i need to calculate the function values with runge kutta. my problem is that i need to choose the h (=dx) such that the error will be in order of 0.0001. how i choose ...
10
votes
0answers
137 views

A hypergeometric puzzle

$$ 143\,\sqrt {3}\;{\mbox{$_2$F$_1$}\left(\frac{1}{2},\frac{1}{2};\,1;\,{\frac {3087}{8000}}\right)}= 40\,\sqrt {5}\; {\mbox{$_2$F$_1$}\left(\frac{1}{3},\frac{2}{3};\,1;\,{\frac ...
8
votes
2answers
444 views

Prove that the Dirichlet eta function is monotonic

Let us consider $\eta(p):= \sum\limits_{n=1}^\infty \frac{(-1)^{n+1}}{n^p}$ for $p>0$. Has anyone come along with an elementary proof that $\eta(x)$ is monotonically increasing on this set? By ...
5
votes
1answer
108 views

Ham sandwich theorem for discrete measures - reference request

A discrete version of the ham sandwich theorem states as follows (see for instance "Common Hyperplane Medians for Random Vectors" - Hill): For every $\mu_1,...,\mu_n$ discrete (i.e., purely atomic) ...
1
vote
1answer
67 views

An identity for the exponential of a martingale

I am trying to understand a Lemma in Olav Kallenberg's book "Foundations of Modern Probability" (Lemma 26.19 in the second edition or 23.19 in the first edition). The part of the lemma that I do not ...
0
votes
1answer
82 views

Symmetric Zero-Diagonal Matrices

Consider matrices with entries in a field $F$ of characteristic $2$. Let $\Omega$ denote the $2n\times2n$ matrix $\left[\begin{array}{ll}0&1_n\\1_n&0\end{array}\right]$. Then $X^t\Omega X$ is ...
4
votes
1answer
227 views

The space of varieties between two given varieties

Let $\mathbf{P} = \mathbf{P}^n(k)$ be the $n$-dimensional projective space over a field $k$, let $A, B$ be projective varieties in $\mathbf{P}$ such that $A \subset B$. Now define $V(A,B)$ to be the ...
2
votes
0answers
103 views

State-of-the-art for the descent principle in relation to surfaces over a number field

I'll start with some motivating remarks (edit: as pointed out in the comments, these motivational remarks do not hold for surfaces: there is an example of a conic bundle surface over a real quadratic ...
6
votes
1answer
306 views

Is Gauss sum a p-adic measure?

Let $\Gamma$ be Galois group of cyclotomic $\mathbb{Z}_p$ extension over $\mathbb{Q}$. Consider the function $G$ which sends each finite order character $\chi$ of $\Gamma$ to the Gauss sum $G(\chi)$, ...
3
votes
0answers
179 views

Reference request: Beilinson-Bernstein for finite-dimensional reps and category O

I think I’ve once been told that under the Beilinson-Bernstein correspondence, finite-dimensional representations of a semisimple Lie algebra $\mathfrak{g}$ correspond to (twisted) D-modules on $G/B$ ...
3
votes
0answers
119 views

Subgroup cliques in the Paley graph

It is a famous open problem to estimate non-trivially, for a prime $p\equiv 1\pmod 4$, the largest size of a subset $A\subset{\mathbb F}_p$ such that the difference of any two elements of $A$ is a ...
3
votes
0answers
71 views

Operator theory of initial-value ODE problems

The theory of elliptic boundary value problems is usually treated from the perspective of functional analysis, and the theory of operators between Hilbert spaces. In contrast to that, the theory of ...
-1
votes
0answers
58 views

Confusion about the projected component in an irreducible space in the tensor product decomposition using Littlewood-Richardson?

The regular representation of the symmetric group can be formulated in terms of an abstract tensor, where the action of the symmetric group elements is by means of permuting the indices. Given an ...
1
vote
0answers
18 views

Differential operator with codimension 2 singularity in the domain

The soft version of the question is as follows: suppose I have a linear operator, and I know it is a 'nice' differential operator on its domain minus a singular set of codimension two. Does the ...
-1
votes
0answers
64 views

Deciding whether a space finitely covered by a simple space is again simple [on hold]

Recall that a path-connected $X$ space is said to be simple (or, in Hatcher's terminology, abelian), if the action of $\pi_1$ on $\pi_n$ is trivial for all $n \geq 1$. I've been trying to come to ...
0
votes
0answers
52 views

Speed up Linear programming

I have a linear programming problem like this: minimize $c^t X$ under the constraint that $AX \ge b$. I will need to solve this linear programming problem online many times. I need it to be as fast ...
-2
votes
0answers
113 views

What is geometry? [closed]

My question is "How could we define the notion of Geometry ?", or maybe more precisely "How could we define the notion of a "Geometric Theory ?" Gérard Lang
-2
votes
0answers
67 views

How can this statement of the link between Hamiltonian and symplectic matrices be made more rigorous? [closed]

I quote the a textbook, which says the following: It is easily checked that the exponential of a Hamiltonian matrix $$ g=exp(\phi\cdot\mathbf{T}) $$ is a symplectic matrix; Lie group ...
3
votes
1answer
375 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 ...
1
vote
0answers
46 views

presence of turbulent phenomena in systems of linear pde?

Are there linear systems of PDE that are known to have solutions which exhibit turbulence, or can turbulence be firmly classified as a fundamentally non-linear phenomenon, similar to solitons or shock ...
4
votes
2answers
65 views

Measure on hyperspace of compact subsets

For a Polish space $X$, let $K(X)$ be the set of compact subsets of $X$. Given the topology with basis $\{K\in K(X):K\subset U_0, K\cap U_1\neq\emptyset,\ldots,K\cap U_n\neq\emptyset\}$ for open sets ...
4
votes
1answer
139 views

Sites for seeking possible collaborations

As a material scientist, I have recently constructed algorithms for solving ground state of arbitrary cluster interactions models and prepared publications in the field of physics and material ...
3
votes
0answers
136 views

Category of modules over commutative monoid in symmetric monoidal category

Let $\left(\cal{C},\otimes ,I\right)$ be a symmetric monoidal category (not necessarily closed) and $A$ a commutative monoid in $\cal{C}$. In his DAG III (page 95), Lurie writes: In many cases, ...
2
votes
2answers
86 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 ...
4
votes
1answer
140 views

Totally disconnected subspaces

This question is motivated by this one, where no simple solution within ZFC seems to exist. Let me ask a weaker question then. Suppose that $K$ is a compact, Hausdorff, non-metrizable space. Does it ...
1
vote
0answers
116 views

which sections of elliptic curves are conjugate?

Suppose you have a relative elliptic curves $f : E\rightarrow S$ (say $S$ is connected). Then suppose you have two sections $g,g' : S\rightarrow E$, corresponding to two sections $g_*,g'_*$ to the map ...
0
votes
0answers
76 views

Characterization convex function [closed]

Let be $f:[0,1]\rightarrow\mathbb{R}$ a continuous function such that far all $a,b\in [0,1]$ with $a<b$ $$f\left(\frac{a+b}{2}\right)\leq\frac{1}{b-a}\int_a^b f(x)\,dx.$$ How to prove that $f$ is ...
13
votes
1answer
203 views

Flag complexes that are shellable but not vertex decomposable

As the title suggests, I was wondering if anyone can point me to any examples in the literature to flag complexes that are shellable but not vertex decomposable. It is well-known that if a ...
14
votes
1answer
259 views

Is every elementary absolute geometry Euclidean or hyperbolic?

Absolute geometry is any one that satisfies Hilbert's axioms of plane geometry without the axiom of parallels. It is well-known that it is either the Euclidean or a hyperbolic plane. For an elementary ...
-3
votes
0answers
81 views

Tripet prime reciprocals series [closed]

Does any body know if the series of reciprocals of triplet primes of form p,p+2,p+6 or p, p+4,p+6 converges or diverges. Could this be used as a proof of infinity of twin primes
0
votes
1answer
50 views

Which Hyperspace Topologies Yield Topological Lattices?

At least on a continuum, the binary operations of intersection and union are Vietoris-continuous. But the Vietoris topology only applies the the collection of NONEMPTY closed subsets, and this means ...
-1
votes
0answers
28 views

Mean exit time / first passage time for a general symmetric Markov chain [closed]

Suppose I have a Markov chain as depicted in the following figure: where $N$ is even. State 0 and $N$ are the two sinks of the chain. The transition probabilities have the following property: ...
9
votes
1answer
331 views

Can a division algebra have degree divisible by its characteristic?

I apologize in advance if this is easy, but I've tried Googling, and had no luck. I'm currently working on a proof, and I realized in the course of writing that this proof will break if out there ...
3
votes
2answers
164 views

Morse theory Vs degree theory

I asked this question on http://math.stackexchange.com but no unswers! I have this paragraph from K.C. Chang Infinite dimensional Morse theory In comparison with degree theory, which has proved ...
5
votes
0answers
150 views

Distributivity of group topologies on $\Bbb Z$

Let $\mathcal L$ be the set of all group topologies on $\Bbb Z$. It is known that $(\mathcal L,\subseteq)$ is a modular complete lattice. Is $(\mathcal L,\subseteq)$ distributive?
0
votes
1answer
74 views

Estimates on gamma- functions [closed]

I need a special inequality related to a fractional derivative problem. Let k∈ℕ ,0<α<1 , 0<β<1.Consider : A=[Γ(1-α)Γ(1+k-β)/Γ(2-β-α+k)].(1-α) On what conditions (on k ,β and α) A is less ...
0
votes
0answers
27 views

Beta distribution - changes in multiple time points

Let's say I have a set of daily data (assume iid) that I know is beta distributed (between 0 and 1). I can estimate the parameters of the distribution and calculate the tails etc. This would tell me ...
-1
votes
0answers
64 views

I need help in understanding O(nlogn) question [closed]

I wish I could think of a better way to word my question. Maybe some one here could offer s suggestion for that, as well. On to my question. Before I do, this is a class question that has been asked, ...

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