# All Questions

**22**

votes

**1**answer

555 views

### Making $\mathbb{Q}$-cohomology integral

Let $X$ be an algebraic variety (say, smooth and projective) over $\mathbb{C}$, and fix $$\alpha\in H^i(X^{\text{an}}, \mathbb{Q})$$
with $i>0$.
Does there always exist a variety $Y$ and a ...

**-1**

votes

**0**answers

17 views

### state of art pseudo-boolean optimization solver [on hold]

I am actually constructing engineer application based on pseudo-boolean optimization. I want to ask what is the current status (how many variables, interaction parameters) the solver could generally ...

**0**

votes

**0**answers

171 views

### A problem of a hacked article [on hold]

I am surprised by the fact that a journal published an article that I have in arxiv for a few months. The date of publication is after the date that I have in arxiv. The submission date in the ...

**3**

votes

**2**answers

311 views

### Intuition behind $\zeta(2) = \frac{\pi^2}{6}$ [on hold]

In literature, there are many proofs of the well-known result $$\zeta(2) = \frac{\pi^2}{6}.$$
However, as far as I know, they do not offer an intuitive explanation of why this result should be true. ...

**2**

votes

**3**answers

329 views

### How did the summation operation come into use? [on hold]

So we've been using summations at least since the dawn of calculus. I'm wondering how the process of summing a function came to be known? Are there events that led to the invention of the summation ...

**1**

vote

**1**answer

155 views

### Quotients and radicals

Let $I, J$ be ideals in a commutative ring with identity $R$. Define the quotient ideal $(I : J)$ by $$(I : J)=\{x\in R : xJ\subseteq I\}.$$
Define the radical $r(A)$, of an ideal $A$ of $R$ by
...

**-3**

votes

**0**answers

31 views

### Operations research and Linear Programming [on hold]

I am working on a linear programming maximization problem and need help in understanding how to reformulate this problem so that it has only two functional constraints and all variables have ...

**-1**

votes

**0**answers

73 views

### Combinatorial Proof Problem [on hold]

I'm having trouble solving this because I'm only familiar with algebraic proofs instead of combinatorial.
$$\binom{3n}{3}=n^3+6n\binom{n}{2}+3\binom{n}{3},\quad\text{for }n\ge3.$$

**4**

votes

**0**answers

60 views

### The name for the quotient property

I asked this question on math@stackoverflow and was suggested to ask it here as well.
We call a surjective $f:X\rightarrow Y$ a quotient mapping if it satisfies, for every $U\subset Y$
...

**-1**

votes

**0**answers

64 views

### How to prove that the vertices of a convex hull are only defined by some specific subsets, in this particular case [on hold]

Let $\mathbb{V}$ a vector space of dimension $2^N$, where each vector (of size $N$) is a combination of $0$ and $1$. ex: for $N=2$, $\mathbb{V}$={[0 0],[1 0],[0 1],[1 1]}.
Consider (in ...

**15**

votes

**2**answers

512 views

### Teaching the fundamental group via everyday examples

This is a "prequel" to a similar question about homology. Both questions were inspired by seeing a talk, by Tadashi Tokieda, about the interesting physics that appears in toys.
What stories, ...

**2**

votes

**1**answer

122 views

### Various definitions of the Bruhat decomposition of the affine Grassmannian

Let $G$ be a connected, simply connected, complex, semi-simple group with affine Grassmannian $\mathcal Gr \cong G(\mathbb C[t,t^{-1}])/G(\mathbb C[t])$. Fix a choice of maximal torus $T \subset G$ ...

**3**

votes

**0**answers

62 views

### A problem on chains of squares — can one find an easy combinatorial proof?

Consider the unit square $ S = [0,1] \times [0,1] $. For each $ n \in \mathbb{N} $, we can tessellate $ S $ by the collection
$$
A
= \left\{
\left[ \frac{i}{n},\frac{i + 1}{n} \right] \times
...

**0**

votes

**0**answers

135 views

### Publishing in mathematics [on hold]

I apologize if mathoverflow is not the right place for this question, but I guess it is the only place where I can get an answer.
The question is the following: is publishing a paper in mathematics ...

**-1**

votes

**0**answers

35 views

### Conformal map from a sector of unit disk onto upper half plane [on hold]

How do we construct a conformal map from $\{z=x+iy,x>1/2,|x+iy|<1\}$ onto the upper half plane? My idea is first create a sector sending one of the two intersection points to infinity.Any help ...

**3**

votes

**3**answers

455 views

### What should be considered a finite size of an infinite dimensional space? [on hold]

I've got a map between two infinite dimensional spaces, $f: A\to B$, where $A$ seems "larger" than $B$. For the sake of conversation let's assume that $A$ is the set of smooth maps $\mathbb R^3\to ...

**3**

votes

**1**answer

85 views

### Ising model: probability of a long path of minus under plus boundary conditions

Consider for example the Ising model on a square lattice. Fix zero magnetic field and plus boundary conditions.
Low temperature, one minus spin. With a Peierls argument one can prove that, given a ...

**-2**

votes

**0**answers

89 views

### The field of rational functions on a smooth projective absolutely irreducible curve over a finite field [on hold]

We mean a variety (over "k") of dimension 1 by the curve in the expression "The field of rational functions on a smooth projective absolutely irreducible curve over a finite field k", don't we?

**9**

votes

**2**answers

315 views

### Splitting integers 1, 2, 3, … n to avoid least possible sum

For each positive integer n, partition the integers 1, 2, 3, … 2n into two sets of n integers each. Let g(n) be the least integer such that there is such a partition in neither of whose parts there is ...

**2**

votes

**0**answers

61 views

### What is the significance of the median eigenvalue?

When I look at the spectral density plots of my (usual) laplacian graphs, they spike at the median eigenvalue. But what significance for the graph/matrix (which originates from a network) does the ...

**10**

votes

**2**answers

123 views

### Which real Pin groups agree?

In the Lie theory notes on my website it is claimed (Example 7.3.3.5) that $\mathrm{Pin}(4,0)$ and $\mathrm{Pin}(0,4)$ are not isomorphic. As Nigel Ray pointed out to me, this claim is not quite ...

**0**

votes

**0**answers

51 views

### Generalized weight space

In their paper Lepowsky and Mcmollum sketch theory of weights in a more general setting. Here is their definition of a weight space:
If $A$ is a subset of $\mathfrak g$ and $\lambda$ is a function ...

**0**

votes

**0**answers

45 views

### Green's function of the Ornstein-Uhlenbeck operator

Consider $\mathbb R^d$ with the Gaussian measure $d\gamma(x) = e^{\frac{1}{4}|x|^2}\,dx$. The Ornstein-Uhlenbeck operator $L$ is given by
$$
Lu = \Delta u- \frac{1}{2}x\cdot \nabla u.
$$
Is there a ...

**1**

vote

**0**answers

42 views

### Ozsvath-Szabo orientation convention for Seifert fibred spaces

I am confused by the orientation convention that Ozsvath and Szabo use in On Heegaard Floer homology and Seifert Fibered Surgeries and would appreciate if someone clarifies this for me. On page 15 ...

**0**

votes

**0**answers

43 views

### Which of the following is true? [on hold]

$f(x),g(x)$ are defined on $[-1,1]$, $f'(0),g'(0)$ exist, $f(0)=g(0)$, and $f(x)\ge g(x)$ holds for an open interval containing $0$. Then which of the following is correct:
I, $f(x)$ and $g(x)$ have ...

**2**

votes

**0**answers

59 views

### Hitting time of two dimensional continuous martingale

Let $(\Omega, \mathcal{F}, P)$ be a probability space, on which $\mathcal{F}_t$ is filtration satisfying general conditions. $W_{t}=\left(W_{t}^{1},W_{t}^{2}\right)^{T}$ is a two dimensional Brownian ...

**2**

votes

**1**answer

55 views

### Limit-circle and limit-point at endpoints

I was wondering if the following holds:
If you have an ODE $$-y''(x) + q(x) y(x) = \lambda y(x)$$ on a finite interval $(a,b)$ and you know that this equation is limit-circle or limit-point at the ...

**2**

votes

**1**answer

118 views

### A question about running MMP with scaling

Let $\pi:X \to U$ be a projective morphism, and $(X, \Delta = A + B)$ be a KLT pair, where $A$ is a general ample divisor and $B$ is effective.
Suppose $K_X + \Delta$ is not nef (over $U$) and there ...

**0**

votes

**0**answers

24 views

### question about Baer sum of extensions

Let $E_1$ and $E_2$ be extensions of $\mu_p$ by $\mathbb{Z}/{p\mathbb{Z}}$. Assume that $E$ contains $E_1$ and $E_2$ both, and $E_1 \cap E_2 = \mathbb{Z}/{p\mathbb{Z}}$.
Then, does $E$ contain their ...

**1**

vote

**0**answers

129 views

### Is there any progress on Problem 13 (from Schoen and Yau)?

This is closed related to the question asked here. I wonder if there is any progress on Problem 13 from the "Problem Section" in Schoen and Yau, page 281, problem 13, which asks:
Let $M_1$ and $M_2$ ...

**3**

votes

**1**answer

121 views

### Real points of zero-dimensional real algebraic varieties

There have been a number of discussions of zeros of random polynomials here (the most recent being: Why do roots of polynomials tend to have absolute value close to 1?).
Here is a closely related ...

**1**

vote

**0**answers

33 views

### Classification properties of fusion rings

Fusion rings have so many classification properties (I checked the literature a bit) that my head hurts. For practical reasons I define the following three new properties (which might coincide with ...

**-3**

votes

**0**answers

32 views

### Does $(n + 2)$ have a multiplicative inverse mod $(n - 1)$ over $GF(5)$? [on hold]

I have been stuck on understanding this for hours. The reason I am confused is that I thought over $GF(k)$, only constants have inverses. Also, how would one go about applying EGDC to figure this out? ...

**-2**

votes

**0**answers

75 views

### Closure in Hilbertspace [on hold]

I know that i asked this question already on stackexchange.com (http://math.stackexchange.com/questions/983377/closure-in-a-hilbertspace)
Define for a pure contraction $S$ (remember: $\|S\|\leq1$ and ...

**8**

votes

**0**answers

143 views

### Mixed Hodge structure on configuration spaces

Let $X$ be a smooth complex projective variety. Let $F(X,n)$ be the configuration space parametrizing $n$ distinct ordered points in $X$. The cohomology groups $H^k(F(X,n),\mathbf Q)$ carry a mixed ...

**0**

votes

**0**answers

43 views

### Estimation of growth rate of spectral radius

I have following problem: Let the spectral radius of $S=(a_{ij})_{n\times n}$ be $\lambda>1$, where each $a_{i,j}$ is a positive integer, then we have that
$$\lim_{k\to ...

**3**

votes

**1**answer

154 views

### Chances for a cosine polynomial to be positive at a point

Let $k_1,\ldots,k_n$ be distinct integers. Let $s_n(t)=\cos (k_1t)+\cdots+\cos (k_nt)$ be a trigonometric sum. Consider any interval $I\subset [-\pi,\pi)$ of length $\delta=\delta(n)$. Let $\,U$ be a ...

**1**

vote

**0**answers

27 views

### How to define Product of Conditional Measures?

I have been wondering how to define the product of conditional measures as defined by Renyi-Popper. I spell the details below.
If $(X,\Sigma)$ is a measurable space, then the function $\mu : ...

**2**

votes

**0**answers

52 views

### Number of maximal chains in Bruhat order

Is there a formula for the number of maximal chains between two permutation in the (strong) Bruhat order?

**5**

votes

**0**answers

72 views

### Picard scheme of varieties over imperfect fields

Let $k$ be a field and $X$ a proper $k$-scheme. It is a theorem of Murre and Oort that the Picard functor is representable by a $k$-group scheme $\operatorname{Pic}_{X/k}$ which is locally of finite ...

**3**

votes

**0**answers

40 views

### Reference for existence results for 2D forced viscous Burgers equation

I am looking for results concering the following parabolic PDE
$$u\cdot\nabla u + \Delta u = F(x),$$
where $$u\colon\Omega\to\mathbb{R}^2,$$ and $\Omega\subset\mathbb{R}^2$ is a 2D domain (bounded or ...

**1**

vote

**2**answers

148 views

### Calculating Exterior Distance from Measurements of Inner Geometry

Gauss has proven in his famous Theorema Egregium, that it is possible, to calculate the gaussian curvature from measuring angles and distances on the surface, irrespective of how the surface is ...

**1**

vote

**1**answer

62 views

### Integrals involving trigonometric functions and polynomes

Let $P(x)$ be a real polynome. Specify all such $P(x)$ that one of the next integrals converge:
$$
\int_0^{\infty} sin(P(x))dx, \int_0^{\infty} cos(P(x))dx ?
$$
Among special cases are such ...

**1**

vote

**1**answer

79 views

### On the Saito Kurokawa representation

I know Saito-Kurokawa(SK) representation is the famous non-tempered representation of $SO(5)$. But since the tempered or non-tempered terms are concerned with local phenomenon, I am wondering that ...

**3**

votes

**1**answer

152 views

### A number array related to colored necklaces and the primes

I stumbled upon entry OEIS-A208535 on the enumeration of certain kinds of colored necklaces and noticed that the integers for the odd prime rows of the table there seem to be given by the Moreau ...

**4**

votes

**1**answer

125 views

### Reference request: Invariant sets of dynamical systems

(I should preface this with the disclaimer that this is a slightly elaborated version of a question that I posted onto math se recently to which I received no responses, and have since deleted the ...

**-1**

votes

**1**answer

42 views

### differential Proper Maps [on hold]

If $K$ is a subset of $M$ we write $M_{K}(M,M)$ for the set of diffferential maps of $M$ into $M$ with support in $K$.If $K$ is compact,then $M_{K}(M,M)$ consists of maps for which the preimages of ...

**0**

votes

**0**answers

29 views

### Questions about some special tensor transformation

Suppose tensor $U_{i\alpha\beta}$ with dimension $M*N*N$ satisfy following condition:
$$U_{i\beta\alpha}=W^1_{\alpha\alpha'}W^2_{\beta\beta'}U_{i\alpha'\beta'}$$
where $W^1$ and $W^2$ are $N*N$ ...

**-4**

votes

**0**answers

52 views

### Lemma on Polish Spaces [on hold]

I asked the following question on StackExchange earlier, but received no replies yet.
Let $(X_1,\Sigma_1,\mu_1)$ and $(X_2,\Sigma_2,\mu_2)$ be probability spaces. Suppose the following conditions ...

**1**

vote

**0**answers

31 views

### Anti-Invariant Polynomials of the Dihedral group

I'm interested in the one-dimensional irreducible representations of $D_{2n}$ acting on $\mathbb{R}[x,y]$. I have found that the trivial representations for an algebra freely generated by $x^2+y^2$ ...