# All Questions

**3**

votes

**1**answer

79 views

### Create matrix containing values in [0,1] where sum of all diagonals and anti-diagonals is fixed

The problem I am facing sounds at first glance pretty simple. However, as very often, it seems more complicated than I first assumed:
I want to calculate a matrix $P = (p_{j,k}) \in \mathbb{R}^{n ...

**0**

votes

**0**answers

53 views

### Action of semidirect products of cyclic groups

Is there anything known about group actions of $C_{p}\rtimes C_{p}^{*}$ on the ring of real polynomials $\mathbb{R}[X_{1},\ldots,X_{n}]$, where $C_{p}$ denotes the cyclic group of order $p$ and $p$ is ...

**5**

votes

**0**answers

153 views

### Are Bökstedt's THH manuscripts available?

In many papers dealing with topological Hochschild homology, the original unpublished manuscripts by Bökstedt are cited. To name one example, in McClure and Staffeldt's On the topological Hochschild ...

**3**

votes

**1**answer

137 views

### When does an irreducible unitary real representation remain irreducible after complexifying it?

Consider a unitary real representation of a Lie group $G$ over a real Hilbert space $\mathcal{H}_\mathbb{R}$
\begin{equation}
\rho:G\rightarrow U(\mathcal{H}_{\mathbb{R}})
\end{equation}
Taking the ...

**-4**

votes

**0**answers

20 views

### Normal distribution [on hold]

To solve such a question
$\int_{-\infty}^{\infty}\ln{x}\frac{1}{\sqrt{2\pi}\sigma}\exp(-(x-\mu)^2/2\sigma^2)dx$.
It is easy when $\ln{x}$ is replaced by $x$ or $x^2$, but now I have no clue at all. ...

**1**

vote

**0**answers

31 views

### Green's function for fractional Laplacian

Consider the fractional differential equation
\begin{align}
D_{|x|}^\alpha u(x) +bu(x)=f(x)
\end{align}
with $0<\alpha<2$ on an unbounded domain. Instead of $D_{|x|}^\alpha$ one also often sees ...

**-2**

votes

**0**answers

32 views

### Problem on cohomology [on hold]

I am studying the book "Local Cohomology" written by M. R. Brodmann & R. Y. Sharp.
In exercise 2.2.9 in the page 28, asked to complete the proof of 2.2.8(iii) via proving
...

**7**

votes

**1**answer

314 views

### Explicit counter example to Vopěnka's principle in the constructible universe?

Vopěnka's principle is a large cardinal axiom which has many equivalent formulations. One of them, which I find especially appealing, is the following: if the universe is satisfies Vopěnka's principle ...

**0**

votes

**2**answers

136 views

### étale cohomology via Cech cocycles for a quasi-projective scheme

I am looking for the explicit reference to the fact that for a quasi-projective scheme a class in the étale cohomology of a sheaf of a certain degree can by computed using Cech cocycles.

**-1**

votes

**0**answers

40 views

### Hopf formula for the direct product of groups [on hold]

Let $G$ be a finite group with free presentation $1 \rightarrow R \rightarrow F \rightarrow G \rightarrow 1$. Then, we have well known Hopf formula $H_2(G,\mathbb{Z})=(R \cap [F,F])/[F,R]$.
Now, ...

**3**

votes

**2**answers

228 views

### Topologies for which $\mathcal{M}(X)\otimes \mathcal{M}(Y)$ is dense in $\mathcal{M}(X\times Y)$

Are there complete TVS topologies for which $\mathcal{M}(X)\otimes \mathcal{M}(Y)$ is dense in $\mathcal{M}(X\times Y)$
This question is strongly linked to
is the space of all borel measures on ...

**0**

votes

**0**answers

25 views

### Grouplike elements in dual weak Hopf algebras

It is said in D. Nikshych's paper On the structure of weak Hopf algebras (arXiv:math/0106010) that if $A$ is a finite dimensional weak Hopf algebra, then a functional $\gamma$ in the dual (weak Hopf) ...

**0**

votes

**1**answer

45 views

### Lebesgue covering dimension for locales

A space $(X,\tau)$ is said to have Lebesgue covering dimension $\leq n$ (for some $n\in\mathbb{N}$) if every open covering $\cal U$ has a refinement $\cal V$ such that for every $x\in X$ the set ...

**-2**

votes

**0**answers

22 views

### Find points which form angle X from a triangle formed by 2 other points [on hold]

Here's a diagram (I can't post images)
Diagram
Given angle ACB, angle CAD, position C, and position E, and given that angle ADB equals angle ACB, find position D.

**5**

votes

**1**answer

119 views

### Synthetic projective definition of cubic curves

In a synthetic (Pappian) projective plane, one can define a conic in various clever ways not referring to coordinates. For instance, if $f$ is a projectivity from the pencil of lines through a point ...

**1**

vote

**0**answers

77 views

### Matrix norm on $L^p$ operator algebras

I have a question about the framework of $L^p$ operator algebras ($1<p<\infty$), i.e. norm-closed subalgebras of $B(L^p(X,\mu))$ for some measure space $(X,\mu)$ (see e.g. ...

**4**

votes

**0**answers

83 views

### A digraph related to permutations

A finite sequence of distinct real numbers of length $n$ determines a linear order of $\{1,\ldots,n\}$, by mapping position to rank; call this the permutation of the sequence.
Consider the following ...

**0**

votes

**0**answers

38 views

### To determine whether an ideal is prime using Macaulay 2 [on hold]

I am new to Macaulay2, it seems to me that I cannot use it to determine whether an ideal in the polynomial ring over complex number is prime or not, because when I use the isPrime function, I got the ...

**0**

votes

**0**answers

45 views

### An inequality regarding expectation of random variables [on hold]

Let $X,Y$ be positive-valued, well-behaved random variables. Further, let $g(\cdot) \ge 0$ and $f(\cdot)\ge 0$ be two functions and $E(\cdot)$ denotes expectation operator.
I am trying to prove the ...

**2**

votes

**0**answers

111 views

### When is it appropriate to name something a 'fundamental lemma'? [on hold]

The term 'fundamental lemma' refers to many results in mathematics. I don't know too many results referred to by that name, but I am familiar with, for example, the 'fundamental lemma of sieve theory' ...

**4**

votes

**1**answer

49 views

### Largest regular $k$-simplex inscribed in a $d$-cube, $k < d$

The largest (by edge length) regular simplex inscribed in a unit cube
is well known in $\mathbb{R}^2$ and $\mathbb{R}^3$:
Image sources:
left: NMSU,
right: Mathworld.
A recent ...

**0**

votes

**0**answers

39 views

### Is the following “section-wise” defined function measurable in the product space?

I asked this question in mathstackexchange a couple of days ago. Almost right after posing it a partial (affirmative) answer came to my mind in the following form
Proposition: Assume that ...

**3**

votes

**1**answer

166 views

### Finite field “contour” sum

Let $\Bbb{F}_q$ be a finite field. Choose a non-square $\delta \in \Bbb{F}_q^*$
and form the quadratic extension $\Bbb{F}_q\big( \sqrt{\delta} \, \big)$. For
an element $z \in \Bbb{F}_q\big( ...

**2**

votes

**2**answers

48 views

### Volume of a region given by a Constraint Satisfaction Problem

I have a Linear Constraint Satisfaction Problem i.e. I have variables $ x_1, x_2,...,x_m$, with corresponding domains $D_1,D_2,...,D_m $ satisfying linear constraints $C_1, C_2,...,C_n$ with $n ...

**3**

votes

**0**answers

86 views

### Deformation of vector bundle on projective space with same Hilbert polynomial as multiple of structure sheaf

Let $E$ be a vector bundle on projective space ${\bf P}^n$ whose Hilbert polynomial is the same as $\mathcal{O}^{{\rm rank}(E)}$.
Does there exist a vector bundle over ${\bf P}^n \times {\rm ...

**1**

vote

**0**answers

54 views

### Determining the primitive ideal space of C-star algebras

Is there a general way of finding a primitive ideal space of $C^*$-algebra?
For example, if $C^*$-algebra is given by the universal $C^*$-algebra generated by two self-adjoint unitary elements, how ...

**0**

votes

**0**answers

44 views

### Morphism of modules of sections and pullback bundles

I'v asked this question on StackExchange but unfortunately nobody answered. I thought that maybe it would be more apropriate to post it here:
so suppose that we have a morphism $\theta: \Gamma(B,E_1) ...

**0**

votes

**0**answers

33 views

### Betti numbers over unital rings [on hold]

Is the following statement correct?
Given a manifold M. If H_1(M,Z) is a finite cyclic group, then the first R-betti number b_1(M,R) is bounded from above by 1 for every unital ring R.

**2**

votes

**1**answer

68 views

### Functions that are easy to compare to a norm

Let $X$ be a subset of $\mathbb{R}^d$, let $\|\cdot \|_p$ be a norm with $1\leq p\leq\infty$, and let $f:\mathbb{R}^d\to\mathbb{R}$ be a function. I'm trying to find examples of $X$, $p$, and $f$ for ...

**0**

votes

**0**answers

69 views

### Help finding paper: De Concini, Kac - Quantum Groups at roots of 1

I am looking for a specific paper, that I have found very difficult to trace.
C. De Concini, V. Kac - Quantum Groups at roots of 1
Specifically, the paper is cited as follows (on De Concini's ...

**5**

votes

**0**answers

76 views

### The Maximum Number of Lines Contained in the Point Set of a Finite Projective Plane

Consider a finite projective plane of order $q$. Define $f(m)$ to be the maximum number of lines completely contained in any point set of size $m$, where $1 \leq m \leq q^2+q+1$. I would like to ...

**2**

votes

**0**answers

61 views

### Mean on compact metric spaces

Let $X$ be a compact metric space. A $k$ mean on $X$ is a continuous map $f:X^{k}\to X$ which is identity on the diagonal and is invariant under all $k$-permutations. For details, See the following ...

**5**

votes

**2**answers

72 views

### “Relative cone types” for groups relative to some collection of subgroups

It is a well known fact that an infinite hyperbolic group contains an element of infinite order (see e.g. Bridson, Haefliger, Metric spaces of non-positive curvature, Prop. 2.22 on p. 458)
I am ...

**0**

votes

**0**answers

18 views

### Weak continuous convergence of operators [migrated]

Let $T_n$ and $T$ be linear maps from Banach space $X$ to a Banach space $Y$.
Suppose $T_n$ satisfies $T_nx \to Tx$ (convergence in the $Y$ norm) for all $x \in X$.
Let $x_n \rightharpoonup x$ in ...

**0**

votes

**0**answers

25 views

### Morphisms between lax wedges

In the paper
BOZAPALIDES, S., Les fins cartésiennes
the following definition of a lax wedge for a 2-functor $S\colon \mathcal{A}^{op}\times \mathcal{A}\to \mathcal B$ between 2-categories is ...

**1**

vote

**0**answers

20 views

### Question about the characteristics of semimartingales

Let $D=D([0,1,R)$ be the space of cadlag (right-continuous with left limits) functions defined on [0,1] and $X:=(X_t)_{t\in [0,1]}$ be the canonical process on $D$, i.e. $X_t(x)=x(t)$ for all $x\in ...

**4**

votes

**2**answers

141 views

### First collision time of $n$ random walkers on a cycle

My question is somehow related to the one here First Collision Time for k Random Walkers on a Torus but, unfortunately, the answer does not cover my concern.
My problem is: consider $n$ walkers on ...

**3**

votes

**0**answers

278 views

### Explicit Galois Action for $X^3 - X -1$ [migrated]

I have always been frustrated with how indirect discussions of Galois Theory are in Algebra textbooks. Even in fine treatments such as Miles Reid.
Are there any good examples where we can draw ...

**-1**

votes

**0**answers

30 views

### Rank of finite solvable group [migrated]

I am very interested in the following question.
Is there a finite solvable group G with the property that rank G - rank G_ab > n for n > 2? Here G_ab denotes the abelianization of G. For all the ...

**-1**

votes

**0**answers

36 views

### Singular projective variety where the Cartan homomorphism is not an isomorphism?

Let $V$ be an projective variety. Let $\mathcal{O}_V$ be its usual structure sheaf of regular rational functions of degree zero. Let $\mathrm{Coh}\, V$ be the the category of coherent sheaves of ...

**7**

votes

**1**answer

310 views

### Is this theorem on $L$-functions known?

Notations For $f$ a meromorphic function on a domain $\Omega\subseteq \textbf{C}$, we shall say for convenience that $f$ is represented by an Ordinary Dirichlet Series (ODS) if $f$ can be written ...

**0**

votes

**0**answers

24 views

### Any material out there on *spatially* second-order cellular automata? [on hold]

My model of a problem I'm working on took me to needing a spatially second-order cellular automaton (ie, x[i][t+1] is determined by x[i][t], x[i-1][t], x[i-2][t], x[i+1][t], and x[i+2][t]) (also, this ...

**2**

votes

**0**answers

99 views

### Hodge numbers of non-commutative varieties

Let $(X, \mathcal{A})$ be a non-commutative variety, by this I mean $X$ is a (smooth) algebraic variety and $\mathcal{A}$ is a sheaf of algebra on $X$. One such example in my mind is when $X$ admits ...

**17**

votes

**3**answers

1k views

### A Polynomial With Positive Prime Density

Let $P(x)$ be a non-constant polynomial with real coefficients.
Can natural density of
$$\{n\ |\ \lfloor P(n)\rfloor \ \text{is prime.}\}$$
be positive?

**0**

votes

**0**answers

15 views

### Determinant of a 5x5 matrix [migrated]

I have a little problem with a determinant.
Let $A = (a_{ij}) \in \mathbb{R}^{(n, n)}, n \ge 4$ with
$$a_{ij} =
\begin{cases}
x \quad \mbox{for } \,i = 2, \,\, j \ge 4,\\
d \quad \mbox{for } ...

**2**

votes

**0**answers

128 views

### Squarefree part of a Mersenne number

Consider the Mersenne number; $M_p=2^p−1$.
Let $M_p=a_pb^2_p$ where $a_p$ is positive, squarefree, and $p$ is prime.
A chinese paper written by Le Maohua "“On Mersenne Numbers”" states that the ...

**11**

votes

**2**answers

231 views

### A measure on the space of probability measures

This question was originaly posted in the stackexchange https://math.stackexchange.com/questions/1226701/a-measure-on-the-space-of-probability-measures but since it only got a comment I decided to ...

**-1**

votes

**0**answers

104 views

### Non-flat fibration - 1. fibres still homotopic? 2. references/examples? [on hold]

I stumbled over fibrations $\pi: E\rightarrow B$ that are not flat, i.e. where the dimension of the fibre $\pi^{-1}(b)$ jumps over certain points $b \in B$. Are these still 'ordinary' fibrations in ...

**3**

votes

**1**answer

53 views

### Takahashi convex metric spaces

A Takahashi convex metric space is a metric space $(X,d)$ such that $\exists W : X \times X \times [0,1] \rightarrow X$ that satisfies :
$d (u, W(x,y; \lambda)) \leq \lambda d(u,x) + (1- \lambda) ...

**7**

votes

**1**answer

135 views

### Determinant of a checkerboard Hankel matrix with Catalan numbers

My goal is to compute
\begin{equation}
I = \det \left(\mathbf{I} + \mathbf{A}\right)
\end{equation}
where $\mathbf{A}$ is a $n \times n$ checkerboard matrix filled with Catalan numbers:
$$
\left\{
...