# All Questions

**0**

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44 views

### Dimension of a trajectory in $\mathfrak{su}(n)$

Consider $a,b \in \mathfrak{su}(n)$, a fixed positive real number $t$ and the equation:
$\frac{d U(s,t)}{ds} = \left(a + \omega(s)b \right) U(s, t)$ (where $U(t,t)=I$)
and the definition:
$B(s) = ...

**1**

vote

**2**answers

113 views

### Sum of two unbounded self-adjoint operators

Let $A$ and $B$ be two unbounded self-adjoint operators. From this mathoverflow post, for instance, we know that $A + B$ is self-adjoint on $\mathcal{D}(A) \cap \mathcal{D}(B)$ if $A$ and $B$ are ...

**1**

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**0**answers

112 views

### Vector bundle is semistable if only if it's pull back is semistable?

If $X$ is a smooth projective variety and $D$ is a divisor on $X$, and let $i:D\longrightarrow X$ be the closed immersion. Let $E$ be a vector bundle on $X$. Are there any theorems which say that $E$ ...

**4**

votes

**1**answer

172 views

### Young tableau with no i in row i, name that derangement

This question has its genesis in a group assignment: $k$ students are to be given oral exams. Each student will be asked one distinct question from $n$ questions given to them earlier, no two students ...

**0**

votes

**0**answers

35 views

### Initial value problem with unique solution and rear wheel of a bike problem [on hold]

Consider $I\subseteq\mathbb{R}$ an arbitrary interval (it can be of the following types: $[a,b], [a,b), (a,b], [a,+\infty),(a,+\infty),(-\infty,b), (-\infty, b], \mathbb{R}$).
Let ...

**13**

votes

**1**answer

392 views

### When complex conjugation lies in the center of a Galois group

Let $K \subseteq \mathbb{C}$ be a number field (I'm fixing an embedding), and assume $K/\mathbb{Q}$ is Galois with Galois group $G$. Let $\tau \in G$ denote complex conjugation. This question ...

**0**

votes

**0**answers

27 views

### Reparametrization with non-vanishing lateral derivatives [on hold]

Let $\mathbf{r}:I\subseteq\mathbb{R}\to\mathbb{R}^2$ be a $C^{1}(I)$ function, non-constant on any subinterval, such that $\forall\ t_0\in I$, the following limits exist:
$\lim\limits_{t\nearrow ...

**-2**

votes

**0**answers

35 views

### Find a shortest way between nodes in graph [on hold]

I have a next structure :
Each node in graph may have more than 2 links. I want to find a shortest way with node 1 and 13.
...

**6**

votes

**2**answers

82 views

### Reference request: monochromatic paths in edge-colored complete graphs

Given $k,c \in \mathbb{N}$, let $P(k,c)$ be the minimum $n$ such that no matter how we color the edges of the complete graph $K_n$ with $c$ colors, there is always a monochromatic path of length $k$.
...

**1**

vote

**1**answer

82 views

### Push-forward of sum of two maps

Let $X=R^n$ and $Y=R^m$ are two Euclidean spaces with $m<n$. Let $\varphi$ and $\phi$ are two (smooth) maps from $X$ to $Y$ and $\mu$ is a probability measure on $X$. Is there any relationship ...

**1**

vote

**1**answer

89 views

### Are sections of $\tau M$ differential operators on the exterior algebra?

Let $M$ be a smooth manifold and $\tau M$ its second-order tangent bundle. A second-order vector field $A\in \Gamma(\tau M)$ can locally be expressed as a finite sum of operators ...

**-6**

votes

**0**answers

57 views

### What math do I need to know in order to understand basic trigonometry? [on hold]

Im reaching a point in programing where I need to create basic shapes which I simply cant since my math skills are very bad. After finding out that the skills required are trigonometry I read a few ...

**0**

votes

**0**answers

52 views

### Log-convexity preserved by sum? [migrated]

I'm currently reading Boyd's book on Convex Optimization (free book which can be found here : http://stanford.edu/~boyd/cvxbook/) , and there is one proof I do not understand :
p. 105, the book says ...

**2**

votes

**0**answers

24 views

### The Stratonovich formulation of the Double Mean Reverting Model

I am writing my Bachelor's Thesis on the fast Ninomiya-Victoir calibration of the Double Mean Reverting model and have a question to its Stratonovich formulation. I am new to mathoverflow and a novice ...

**-2**

votes

**0**answers

108 views

### How to use the derived functor to write down a lot of natural morphisms or isomorphisms? [on hold]

In the Kashiwara’s book：Sheaves on manifolds, the derived functor is defined in the abstract form, you can see some discussing at here: Derived functor
Kashiwara’s book gives a lot of natural ...

**3**

votes

**1**answer

82 views

### Is every frame monomorphism regular?

Is every monomorphism in $\mathbf{Frm}$, the category of frames, regular?

**2**

votes

**0**answers

65 views

### Parallelizable nearly-Kahler manifolds

In this question, we have discussed how the following bundle:
$E_{d} = TS^{d}\oplus \Lambda^2 T^{\ast}S^{d}$
is always trivial, where $S^{d}$ is the $d$-dimensional standard sphere. Now, let us take ...

**-2**

votes

**2**answers

59 views

### does a lattice have a minimal item [on hold]

A lattice (L, ≤) is a partially ordered set, where each two elements of the set have a least upper bound and a greatest lower bound. Let's consider the situation where L is finite.
I think that ...

**5**

votes

**0**answers

124 views

### Is there a more general obstruction to the existence of moduli spaces than the existence of automorphisms?

We are taught that, in general:
A type of objects that has nontrivial automorphisms cannot have a fine moduli space.
The proof generally goes along the lines of:
Take an object $X$ with a ...

**2**

votes

**2**answers

117 views

### Is the exterior power of a primitive matrix still primitive?

the question is already in the title. Here some more details.
I have a primitive matrix $M$ (primitive means $\exists k\geq 0$ such that $M^k > 0$). I take exterior powers $\wedge^n M$ and I would ...

**13**

votes

**3**answers

2k views

### A variant of Goldbach Conjecture

I'm asking if this variant of weak Goldbach's Conjecture is already known.
Let $N$ be an odd number. Does there exists prime numbers $p_1$, $p_2$ and $p_3$ such that $p_1+p_2-p_3=N$? Ideally, can we ...

**3**

votes

**1**answer

111 views

### Identify ring of polynomials symmetric under forgetting variables

I came across the following ring $A$, which appears as a Chow ring. I am wondering if it has been studied before; in particular, I am looking for a reference where this object might have been ...

**1**

vote

**0**answers

24 views

### Averaging a log-concave centrally-symmetric function over convex bodies

the question is the following: given a log-concave isotropic function $f$ defined on $\mathbb{R}^n$ and two compact 0-symmetric convex bodies $C_1, C_2$, where $C_1 \subset C_2$. Is it true that
$$
...

**5**

votes

**2**answers

264 views

### Interpretation of the monomorphism $H^2(\pi_1(X),\mathbb{Z}) \rightarrow H^2(X,\mathbb{Z})$

Let $X$ be a nice topological space and denote by $\pi_1(X)$ its fundamental group.
It is well-known that there is a well-defined map
$$
0 \rightarrow H^2(\pi_1(X),A) \rightarrow H^2(X,A),$$
where ...

**4**

votes

**1**answer

107 views

### Extremal, but not regular monomorphism

Is there an example of a category, and a monomorphism $m:X\to Y$ between two objects such that $m$ is extremal, but not regular? (A monomorphism $m:X\to Y$ is said to be extremal if whenever $m=g\circ ...

**2**

votes

**1**answer

73 views

### Does “equalisers always closed” imply $T_2$?

Is there a non-$T_2$ space $(X,\tau)$ with the following property?
For all topological spaces $A$ and continous maps $f,g:A\to X$ the set $\{a\in A: f(a) = g(a)\} \subseteq A$ is closed.

**3**

votes

**0**answers

159 views

### How to handle a polynomial whose roots exhibit obvious symmetry

I've got a sequence of polynomials, and for each of them the roots obviously follow a definite pattern. Here are the roots of the 34th one
All others have their roots arranged in a similar ...

**3**

votes

**0**answers

101 views

### Are all monomorphisms in the category of bounded lattices regular?

Let $\mathbf{Lat}_{01}$ be the category of bounded lattices with lattice homomorphisms that respect the smallest and the largest element. Is there a monomorphism in $\mathbf{Lat}_{01}$ that is not ...

**2**

votes

**0**answers

62 views

### About some distributive laws in the Bousfield lattice

It is know that for any $\alpha$-well generated tensor triangulated category $\mathcal{T}$ the collection of Bousfield classes forms a set, furthermore this set is a complete lattice, denoted by ...

**1**

vote

**0**answers

73 views

### Size of the eigenfunction of Laplacian (reference request)

It is a classical Sobolev inequality that if $\phi$ is an eigenfunction of the Laplace-Beltrami operator on a $n$-dim compact Riemannian manifold $M$ with eigenvalue $\lambda$ then
...

**5**

votes

**3**answers

264 views

### A conjecture about parallelizable generalized spheres

Let $S^{d}$ denote the standard $d$-dimensional sphere. I heard from a physicist that from physical arguments they have been able to show that the vector bundle:
$E_{d} = TS^{d}\oplus \Lambda ...

**5**

votes

**2**answers

81 views

### Uniquely ergodicity and polynomial ergodic average

Let $(X,T)$ be a uniquely ergodic system (here X is compact, T is a continuous map form $X$ to itself), so for any continuous function $f:X\rightarrow\mathbb{R}$ we have for any $x\in X$, the ergodic ...

**1**

vote

**0**answers

93 views

### Zeros of zeta function

We have that $$\int_{\square} F(s) \frac{\zeta^{\prime}}{\zeta}(s)ds= \sum_{\substack{\zeta(\gamma)=0 \\ \gamma \in \square}} F(\gamma).$$
I was wondering what will this be
$$\int_{\square} F(s) ...

**1**

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**0**answers

76 views

### How does a level set look like when the minimum point of a function degenerate?

I apologize in advance if this question is well-known. I would like to know an explicit example of a compact, connected manifold $M$ and a smooth function $f: M \to\mathbb{R}$ which satisfy the ...

**4**

votes

**1**answer

114 views

### Area enclosed by Brownian motion (without winding number)

The question Average Value of Area Closed by Brownian Motion turned out to be about the Lévy area process, which measures "signed area with multiplicity" enclosed by Brownian motion (e.g. each ...

**7**

votes

**1**answer

100 views

### Is there a Degenerate Dependency Local Lemma?

The Lovasz Local Lemma has several generalizations, with names usually starting with L, such as Lopsided or Lefthanded.
Here I ask whether another possible generalization (for which I could not yet ...

**4**

votes

**2**answers

182 views

### Examples of surface automorphisms with no periodic points

Consider a smooth projective complex surface $S$ with an automorphism $g:S\to S$. A point $p$ is periodic if it has finite orbit under iterates of $g$.
What are some examples of surface ...

**0**

votes

**0**answers

90 views

### Lower order perturbations of 2nd order differential operators

Consider the well-known Hormander's sum of squares $P = \sum_{j = 1}^m X_j^2$, where $X_j$ are vector fields on a compact manifold $M$ of dimension $n$. Also assume, as is usual to this theory, $m ...

**0**

votes

**0**answers

36 views

### Calculating an isotropic deviation [on hold]

Recently I've been studying the Lamb shift effect. At the beginning of mathematical explanation I've faced the problem of calculating the average values of deviation in isotropic medium like ...

**2**

votes

**0**answers

43 views

### A Generalized Version of Maximal Correlation and Hypercontractivity of Conditional Expectation Operator

Given a pair of random variables $(X,Y)$ over a product space $\mathcal{X}\times \mathcal{Y}$, the maximal correlation coefficient is defined as
...

**0**

votes

**0**answers

39 views

### About cartesian closure of lax.functors categories

Let $\mathscr{A}$ a category and $F, G, H: \mathscr{A}^{op}\to CAT$ lax.functors. I wish find a possible "natural correspondence" between categories: $[F\times G, H]_O \leftrightarrow [F, H^G]_O$ ...

**-2**

votes

**0**answers

76 views

### How to integrate complex numbers? [on hold]

Complex numbers have 2 variable so does it's integration entail contour integration or can we integrate assuming one variable to be a constant in terms of the other or do we try to find a relation ...

**11**

votes

**2**answers

425 views

### distribution of $\sqrt{-1} \mod p$

While reading up on quadratic reciprocity, I learned that if $p = 4k+1$ then $-1$ has a square root in $\mathbb{Z} / p \mathbb{Z}$.
Let $r_p$ be an integer with $0\leq r_p < p$ and $r_p^2 \equiv ...

**1**

vote

**1**answer

46 views

### Comparision of two $C^{*}$ algebras associated to a non vanishing vector field on a compact manifold

Let $X$ be a non vanishing vector field on a compact manifold $M$ so we have a one dimensional foliation $F$ of $M$ with orbits of $X$.
This foliation defines a $C^{*}$ algebra $C^{*}(F)$. On the ...

**1**

vote

**0**answers

45 views

### Equivalence of two definitions of weak solution (subtlety with null sets)

Consider
$$y_t - \Delta y = f$$
$$y(0) = y_0$$
with zero boundary condition. Let $a(t,.,.)$ be the bilinear form associated to $-\Delta$. We have two definitions of weak solutions:
We have $y \in ...

**1**

vote

**1**answer

87 views

### A $C^{*}$ algebra associated to a graded $C^{*}$ algebra

A $C^{*}$ algebra $A$ is graded by $\mathbb{Z}_{n}$ iff it can be acted by $\mathbb{Z}_{n}$. So we associate the $C^{*}$ algebra $A\rtimes \mathbb{Z}_{n}$ to a $\mathbb{Z}_{n}$-graded $C^{*}$ ...

**0**

votes

**0**answers

31 views

### Number of ways you can form pairs with a group of people when certain people cannot be paired with each other [migrated]

Let's say you have a group of eight people and you want to form them into pairs for group projects.
There are
8!/(4!*2!)
ways to do it. (8! Is the total ...

**2**

votes

**1**answer

86 views

### Binary algebra, is it possible to partition the elements in GF(2^12) into 65 subgroups closed under addition?

The set of all binary vectors with 12 components forms a field with 2^12 elements containing 000000000000 and another 65*63 elements. Is it possible to partition these elements into 65 subgroups of 63 ...

**0**

votes

**1**answer

98 views

### Is there a closed form for tan(q*pi) with q rational? [on hold]

I'm looking for a closed-form expression for tan (q*pi) for q rational, or an algorithm that generates one, or some other means of compactly describing the closed-form without referencing an infinite ...

**-1**

votes

**0**answers

36 views

### how to calculate the radius of convergence of the p-exponentials of Pulita?

please it is known from the Pulita thesis that the radius of convergence of his pi-exponentials is 1; he used a differential operator which has this pi-exponetial as a solution etc..., but me I ...