# All Questions

**1**

vote

**0**answers

3 views

### Does $\kappa$-Knaster $\implies$ $\lambda$-Knaster, for $\lambda > \kappa$?

Recall that a forcing notion $P$, satisfies the $\kappa$-Knaster if for any $A \subseteq P$ of size $\kappa,$ there is $B\subseteq A$ of size $\kappa$, any two elements in $B$ are compatible.
...

**0**

votes

**0**answers

6 views

### learning about advanced mathmatics

I'd really like to learn to read theorys of mathematics I just don't know where to start I'm very good at math and I pick up on things very well I just don't know where to start

**1**

vote

**1**answer

8 views

### Can there be a tree of height $\omega_2$ having all levels countable, with no cofinal branch?

For many years I had the idea that if a well-founded tree is both very tall and very narrow, then it must have a cofinal branch. For example, it is a fun exercise to show that any $\omega_1$-tree ...

**2**

votes

**0**answers

8 views

### Value of prolate speroidal wave function at 0

I have a very basic question about prolate speroidal wave functions that can be defined as eigenfunctions to the following integral equation:
$$
\lambda\cdot \psi(x) = \int_{-1}^{1}\frac{\sin ...

**0**

votes

**0**answers

24 views

### Is there some quantitative version of interlacing of eigenvalues of a matrix under rank-1 update?

Given a real symmetric matrix $A$ and a vector $v$ of the same dimension we know that the eigenvalues of $A + vv^T$ are left interlaced by the eigenvalues of $A$.
But do we have any quantitative ...

**0**

votes

**0**answers

10 views

### There is no quasiregular diffeomorphism from punctured ball into ring (on the plane)

The idea is to use l2 cohomology as a quasiregular map invariant.
It is easy to see that there are closed 1-forms on the ring which are not exact, but it occures that every closed l2-form
$f_1(x,y)dx ...

**0**

votes

**0**answers

61 views

### Construction of Highly Structured Quotient Objects in Quasicategories

Given a symmetric monoidal quasicategory $C$ and a morphism of $E_n$-algebras $f:A\to B$ in $C$ we can attempt to construct the quotient object $A/B$. If $A$ is augmented, and we're in a discrete ...

**3**

votes

**0**answers

71 views

### Contractibility of regular CW sphere minus open star

Let $S$ be any regular CW decomposition of (a space homeomorphic to) the $n$-sphere, and consider a cell $\sigma$ of dimension $d \in \{0,\ldots,n\}$. Let $S'$ be the regular CW complex which remains ...

**0**

votes

**0**answers

18 views

### The Free Loop Space of a Manifold $M$ when $M$ is not compact

In Klingenberg's Lectures on Closed Geodesics, before constructing the differentiable structure of the free loop space of a compact manifold $M$, he states that:
A large part of the construction ...

**-1**

votes

**0**answers

42 views

### Non-principal ultrafilters preserving infinite joins/meets

There is a theorem (of Tarski, and Rasiowa-Sikorski) that if we consider countably many infinite joins (or meets), call them Q, in a boolean algebra A, then there is an ultrafilter U which preserves ...

**2**

votes

**1**answer

50 views

### Topologies on spaces of distributions and test functions

Let $X$ be an open subset of $\mathbb{R}^n$. Following the notation of Schwartz, we denote $\mathcal{D}$ the space of compactly supported complex-valued smooth functions on $X$ equipped with the ...

**10**

votes

**0**answers

91 views

### Finding a path through real rooted polynomials

This is a lemma I wanted in order to solve Patrizio Neff's conjecture. It turned out to be the wrong way to think about it, but I am still curious if it is true.
Let $z^n+a_{n-1} z^{n-1} + \cdots + ...

**4**

votes

**1**answer

128 views

### Reference for an unbiased definition of a symmetric monoidal category

In the references I know, a symmetric monoidal category is defined as a monoidal category equipped with some additional data, so in particular the monoidal product is a functor
$$
\mathcal{C}\times ...

**1**

vote

**0**answers

22 views

### About properties of polynomials with common interlacing

Say $\{a_1,a_2,..,a_n\}$ and $\{b_1,b_2,...,b_n\}$ be the real roots of two monic polynomials of degree $n$ which have a common interlacing. (say I have arranged the roots in increasing order)
Can ...

**3**

votes

**1**answer

52 views

### Segal maps for Segal precategories

A Segal precategory is just a simplicial space $X:\Delta^{op} \to sSet$ such that its $0$-th space is discrete (i.e. constant). A Segal category is defined everywhere in the literature as a Segal ...

**-1**

votes

**0**answers

67 views

### weakly etale maps [on hold]

Let $k$ be an algebraically closed field.
Consider the map $\phi:X:=\mathbb{A}^{1}\times\mathbb{A}^{\mathbb{N}}\rightarrow Y:=\mathbb{A}^{\mathbb{N}}$
given by $(\lambda,x(t))\mapsto (t-\lambda) ...

**-6**

votes

**1**answer

53 views

### Find the probability that the product of these numbers is a multiple of 3 [on hold]

From the sequence of natural numbers randomly select a pair of numbers. Find the probability that the product of these numbers is a multiple of 3.

**-4**

votes

**0**answers

32 views

### What is the idea behind a projection operator?what does it do? [on hold]

I need the idea behind this not the definitions of the examples can someone help?

**7**

votes

**1**answer

69 views

### Computing a transversal of a subgroup $H$ of $G$ in expected $O(|G : H|^2 \log |G : H| + |H|)$ time

I have the book "Handbook of Computational Group Theory", by Derek Holt, and in it is a section on finding the transversal of a subgroup. Recall a transversal of a subgroup $H$ of $G$ is a single ...

**0**

votes

**0**answers

6 views

### Laplacian Matrix for weighted Adjacency? [on hold]

I have seen definitions for Laplacian matrix in many resources as follows :
L = D − A
where D and A are the degree and ...

**8**

votes

**0**answers

151 views

### Excellent rings

If A is an excellent commutative ring and G is a finite group of automorphisms of A, is the invariant subring A^G still excellent ? I think this is false -- because if not it would probably be written ...

**5**

votes

**1**answer

43 views

### Evolution operator for a linear parabolic equation

Let $A(t)$ be a smooth family of positive definite operators on a Hilbert space $H$. Consider the operator
$$D:= \frac{d}{dt}+A(t)$$
and let $U(t):H\to H$ be the evolution operator, i.e., $U(0)=I$ and ...

**-4**

votes

**0**answers

43 views

### TOPOLOGY DATA ANALYSIS [on hold]

actually i am PHD student and my research in TOPOLOGY DATA ANALYSIS (TDA)
what I dream about to understand this artcile cran.r-project.org/web/packages/TDA/vignettes/article.pdf may you help me:
1- MY ...

**-2**

votes

**0**answers

56 views

### Relation between Kahler form and Kahler potential [on hold]

Let us consider an example. Take $\mathbb{C}^m$ which is identified with $\mathbb{R}^{2m}$. Now, the Kahler form is given by
$$\Omega = \frac{i}{2} \sum_{i=1}^m dz^i \wedge d\bar{z}^i$$
Now, how can ...

**2**

votes

**0**answers

68 views

### The existence of proper schemes under complection

Let $R$ be a regular local ring, $\hat{R}$ be its completion, $X$ be a proper scheme over $\text{Spec}(\hat{R})$. In what case there exist a proper scheme $Y$ over $\text{Spec}(R)$, such that $X$ is ...

**7**

votes

**1**answer

128 views

### Direct proof that $U$ is an $E_\infty$-space

An immediate consequence of Bott periodicity is that the infinite unitary space is an infinite loop space and so an $E_\infty$-space. I wonder if there is a direct proof (not using $U = \Omega^2 U$) ...

**1**

vote

**0**answers

31 views

### why group completion of configuration space is the iterated suspension space

In Lecture notes in mathematics Vol. 533, The homology of $C_{n+1}$-spaces, $n\geq 0$, F. Cohen, page 226, Corollary 3.3:
$\alpha_{n+1}: C(\mathbb{R}^{n+1};X)\to \Omega^{n+1}\Sigma^{n+1}X$ is a ...

**4**

votes

**0**answers

33 views

### Endomorphism algebras of abelian surfaces with real multiplication

Given an abelian variety $A$ over a field $F$, one may consider the ring of endomorphisms $End(A)$, the ring of $F$-rational maps $A \to A$ respecting the group structure on $A$. We may also consider ...

**-5**

votes

**0**answers

50 views

### Has solution of Brocard's Equation n!=m^2-1 [on hold]

Brocard conjecture in 1904 that the only solution of are n=4,5,7. There are no other solutions with .(Berndt and Galway n.d).Another of Brocard’s conjecture is that there are at least four primes ...

**4**

votes

**0**answers

35 views

### Sobolev-Poincaré inequality for curl-integrable functions

Let $B=B(r)$ denote a ball of radius $r$ in $\Omega \subset \mathbb R^d$ and
$$
u_B := \frac1{|B|}\int_B u \, dx.
$$
The standard Sobolev-Poincaré inequality states that if $u \in W^{1,p}(\Omega)$, ...

**6**

votes

**1**answer

62 views

### Infinite graphs with “similar” Hom-sets

Let $G,H$ be infinite simple undirected graphs with the property that for any graph $X$ we have $|\text{Hom}(X,G)| = |\text{Hom}(X,H)|$. Does this imply that $G$ is isomorphic to a subgraph of $H$, ...

**8**

votes

**0**answers

91 views

### The multiplicative group generated by shifted primes

I am asking for references about the following problem.
In particular, it is still open? If not, what is the state of the art result?
Problem 1. Let $\Gamma$ be the multiplicative subgroup of ...

**3**

votes

**0**answers

41 views

### Sparsifiers for 3-term arithmetic progressions

Let $G$ be a finite abelian group of odd order, let $D\subseteq G$, and $\epsilon \in (0,1)$.
For $S\subseteq G$ define
$$
\Lambda(S) = \frac{1}{|S||G|} \sum_{s\in S}\sum_{g\in G} ...

**0**

votes

**0**answers

20 views

### Stochastic gradient descent interleaved with deterministic optimization

I wish to solve
$\min_{x, y_k} \frac{1}{n} \sum_{k=1}^n f_k(x, y_k)$.
where $f_k$ are all smooth and convex.
Using standard stochastic gradient descent (SGD), each iteration I sample a k from $\{1, ...

**1**

vote

**2**answers

123 views

### Algebraic groups “generated” by a Lie algebra element

Here is a definition which I invented and which I would like to understand better.
Let $ A $ be a complex affine algebraic group. Let $ X \in \mathfrak g $ be an element in its Lie algebra. We say ...

**11**

votes

**0**answers

77 views

### Quickest and/or most elementary proof of “principal iff splits completely”?

Let $L$ be the Hilbert class field of a number field $K$, and let $\mathfrak{p}$ be a prime ideal of $K$. Then $\mathfrak{p}$ splits completely in $L$ if and only if $\mathfrak{p}$ is a principal ...

**1**

vote

**0**answers

16 views

### Find paths in a graph that any 2 vertices can be reached through N of them

Given a undirected weighted graph.
I would like to find a finite set of paths (consecutive vertices and edges)
each shorter than L
any two vertices can be reached through at most N(in my case N=4) ...

**5**

votes

**1**answer

80 views

### Iterated sumset inequalities in semigroups

This question is motivated by the following well-known theorems:
Thm (Plünnecke): If $A$ is a finite nonempty subset of an abelian group, then for every $n$ we have $|A^n| \le ...

**1**

vote

**1**answer

83 views

### iterated loop spaces and configuration spaces [on hold]

In the lecture notes by J.P. May, The geometry of iterated loop spaces, Chapter 5, formula (1), (2) and (10), a map
$$
\phi: Hom_T(X,\Omega Y)\to Hom_T(SX,Y)
$$
is defined. And a map
$$
...

**1**

vote

**0**answers

23 views

### Symmetry conjecture for minimal dilatation pseudo Anosov mapping classes

The conjecture is something like the following:
The minimal dilatation among pseudo-Anosov mapping classes on a surface $S_{g,n}$ is realized by $\rho\circ\omega$ where $\omega$ is supported on a ...

**2**

votes

**1**answer

67 views

### References about spectral theory on Hyperbolic space

Can anyone suggest me some books or papers that include details about spectral theory on Hyperbolic spaces or related topics such as scattering theory on Hyperbolic spaces?
After some googling, I ...

**0**

votes

**0**answers

24 views

### Meaning of k-connected directed graphs [on hold]

Is there any existing definition for "k-connected directed graphs"?
Any reference paper?

**-3**

votes

**0**answers

43 views

### If there is in a category $\mathcal{A}$ finite products and equalizers then it has pullbacks [on hold]

My homework consist in showing that "If there is in a category $\mathcal{A}$ finite coproducts and coequalizers then it has pushouts" based on the proof that "If there is in a category $\mathcal{A}$ ...

**-2**

votes

**0**answers

25 views

### simplifying an equation that has infinitesimals [on hold]

I'm trying to understand an equation with infinitesimal changes:
8*X*dX = d(4*X^2)
I think this can be written
$8X\Delta X = \Delta (4(X^{2}))$
I'm guessing going from 8 outside the differential ...

**-3**

votes

**0**answers

50 views

### How to evalute: $\int_0^1 \frac{e^{-ax}}{ax} -\frac{e^{-abx}}{1- e^{-ax}}((1-x)\cos (\pi x) + \frac{3}{\pi} \sin(\pi x)) dx$ and $a, b >0$ [on hold]

How to evalute: $$\int_0^1 \left[ \frac{e^{-ax}}{ax} -\frac{e^{-abx}}{1- e^{-ax}}\left((1-x)\cos (\pi x) + \frac{3}{\pi} \sin(\pi x)\right) \right] dx$$ and $a, b >0$

**-1**

votes

**0**answers

35 views

### how to solve a linear equation (Ax-b)T- lamda(c)? [on hold]

I'm trying to solve an linear optimization problem, it's first order Lagrange condition leas to this equation
$$
(Ax-b)^T A- \lambda C = 0.
$$
Here $A$ is an $m\times n$ matrix, $m>n$, $C$ ...

**6**

votes

**1**answer

127 views

### Question about zeta function of function field in 1 variable over $\mathbb{F}_q$

From my previous question, I know that$$\zeta_X(s) = {{P(u)}\over{(1-u)(1-qu)}}$$for some polynomial $P(u)$ of degree $2g$, where
$X$ is the set of all places of $F$, a function field in one ...

**3**

votes

**3**answers

256 views

### How many primes have the form $(2^p+1)/3$?

Assuming that $p$ is an odd prime. How many primes have the form $(2^p+1)/3$? Is the number finite? Mathematica calculation shows that there are 23 such primes when $p$ ranges over the first 500 ...

**-3**

votes

**0**answers

75 views

### Quotient group of an amalgam [on hold]

If a quotient of a group G is an amalgam then the group G is an amalgam. Is this true or false?
How can we describe a quotient of an amalgam?

**2**

votes

**0**answers

51 views

### Rational curves through a fixed number of points

Let us fix two positive integers $d$, and $N$. Can we determine a third integer $n$ such that given $n$ general points $p_1,...,p_n\in\mathbb{P}^N$ there exists a unique rational curve of degree $d$ ...