# All Questions

**0**

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3 views

### Is there a unique saddle value for a convex/concave optimization?

I asked this question previously in math.stackexchange and couldnt receive any answer. The question is fundamental, though I couldn't find a reference or a proof somewhere.
Here is the question:
...

**2**

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**0**answers

35 views

### Can integers be distorted to make primes more regular?

Given a set $P$ of real numbers $\ge 1$, define the gap among different products in $P$ as
$$g(P) = \inf \big\{\prod_{i=1}^n p_i^{a_i} - \prod_{i=1}^n p_i^{b_i} \mid p_i\in P;\,\, p_i\ne p_j \,\text{ ...

**1**

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13 views

### Is the associated order of a minimal $T_0$ space always total?

Let's call a space $(X,\tau)$ minimal $T_0$ if it is $T_0$ and for every topology $\sigma\subseteq \tau$ with $\sigma \neq \tau$ we have that $(X,\sigma)$ is not $T_0$ any more.
We say $x\leq y$ in a ...

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7 views

### Uniform bound in Faedo-Galerkin method with time-dependent weight in inner product

Let $v_j$ be an orthonormal basis for $V=H^1(\Omega) \subset L^2(\Omega)$ which is orthogonal in $L^2(\Omega)$.
Let $w:[0,T]\times\Omega \to \mathbb{R}$ be a time-dependent weight which is smoooth ...

**-1**

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37 views

### Simple algebras [on hold]

I like to prove the following statement.
Proposition
Let $A$ and $B$ two $K$-algebras such that $ A \otimes_{K} B$ is simple. Then $A$ and $B$ are simple.
Proof
We only proof this proposition for ...

**1**

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17 views

### Infinite non-splittable graphs

Let $G=(V,E)$ be a graph. For $v\in V$ we set $N(v)=\{w\in V:\{v,w\}\in E\}$. We say that $G$ is splittable if there are $S,T\subseteq V$ with $S\cap T=\emptyset$ and $S\cup T = V$ such that
for all ...

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22 views

### What should one “do” to “strictify” a triangle of transformations coming from a lax commutative triangle of functors?

I would like to apologize for this rather stupid abstract nonsense question.
Let $h=f\circ g$ for composable functors $f,g$; assume that there exist left or right adjoints to $f$ and $g$. Then it ...

**2**

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28 views

### Can the first ordinal in which $V\neq HOD$ be $\aleph_\omega$?

Assume that $V\neq HOD$ and let $\kappa = \min \{\alpha\in On \mid \mathcal{P}(\alpha) \not\subseteq HOD\}$.
Clearly, $\kappa$ is a cardinal.
Question: Is it consistent that $\kappa = ...

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23 views

### Multiplying three factorials with three binomials in polynomial identity

I have checked the following identity (1) below for $n\leq 40$ with a computer.
Let $(n)_k$ denote the falling factorial $n(n-1)\ldots (n-k+1)$, let
$Z_n=\sum_{k=0}^n (n)_k x^{n-k}$, and finally let
...

**1**

vote

**1**answer

56 views

### When two Dedekind sums are equal

The (classical) Dedekind sum $s(h,k)$ is defined as
$$s(h,k)=\sum_{r=1}^{k-1}\frac{r}{k}\bigg(\frac{hr}{k}-\Big[\frac{hr}{k}\Big]-\frac{1}{2}\bigg)$$
for $\gcd(h,k)=1$.
A natural question is, when ...

**1**

vote

**1**answer

21 views

### What is the smallest partition lattice PART(M) containing the lattice P(N) of subsets of a finite set of N elements

It's been known for 35 years that every finite lattice can be embedded in a finite partition lattice ( Pudlak and Tuma algebra universalis 1980, Volume 10, Issue 1, pp 74-95). I don't follow the ...

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37 views

### rational cohomology of finite dimensional real grassmannian

Let $G_k(R^n)$, $n>k$, be the finite dimensional real grassmannian. What is the rational cohomology algebra $H^*(G_k(R^n);Q)$? I have searched out that $H^*(BO_k;Q)=Q[p_1,p_2,...,p_[k/2]]$ is the ...

**-5**

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22 views

### Prize allocation of scratch codes to ensure correct number of prizes to give away [on hold]

We would like to give away 100 prizes.
We have 13.5 million codes, divided into 20 categories. To win a person must collect one code in each category. If 15 of those categories have 877,195 codes ...

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**0**answers

42 views

### Finiteness of geometric valuations

I feel the following fact has been used in many argument in algebraic geometry, but I was not be able to prove it or find the precise reference:
Let $X$ be a normal variety, and $Z \subseteq X$ be a ...

**14**

votes

**1**answer

541 views

### Mathematicians wearing hats on arbitrary total orders

I've been pondering the following generalisation of a famous problem (the special case where $T = \mathbb{N})$:
Question: We have some totally-ordered set $T$ of mathematicians, each wearing a hat ...

**1**

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46 views

### How can i change 8_19 to (3,4)-torus knot K(3,4)?

In the knot table, it is well-known that 8_19 is (3,4)-torus knot. But, it is not clear to me. How can i change 8_19 to (3,4)-torus knot K(3,4)? Moreover, it is well-known that braids of two ...

**-2**

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**1**answer

52 views

### Show that among any 6 non-negative integers one can find 2 integers so that their difference is divisible by 5 [on hold]

I have the following question in homework I have been assigned in Discrete Mathematics relating the pigeonhole principle:
"Show that among any 6 non-negative integers one can find 2 integers so that ...

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**0**answers

35 views

### A certain matrix associated to graphs

I am not very familiar with graph theory, but I need some results for my work. Thus, the question is, whether the following has already been studied and where I can find it. Let $G=(V,E)$ be an graph ...

**1**

vote

**2**answers

70 views

### Partial Sum of the Binomial Theorem [duplicate]

The binomial theorem states $\sum_{k=0}^nC_n^kr^k=(1+r)^n$. I am interested in the function \begin{equation}
\sum_{k=0}^mC_n^kr^k, \quad m<n
\end{equation}
for fixed $n$ and $r$, and both $m$ and ...

**1**

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**0**answers

23 views

### Classes of knots that have known Bridge spectra

Bridge spectra is a knot invariant first defined by Doll, who established some basic properties. Tomova has shown that high distance knots have bridge spectra $(n,n-1,\ldots,2,1,0)$. Zupan has ...

**3**

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37 views

### Matroid rank decay

Consider a uniform vector matroid $M(0)=U_{m,n}$ of rank $m$ with $n$ points, $n>m>2$ (you can think of it as a set of $n$ points in general position in vector space $F^m$ for some large field ...

**2**

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27 views

### Applications of small Kakeya sets over finite fields

It was proved by Dvir that a Kakeya set in $\mathbb{F}_q^n$ has size at least $q^n/n!$, a bound which was later improved to $q^n/2^n$.
For $n = 2$ and $q$ odd the exact bound is $q(q+1)/2 + (q-1)/2$ ...

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45 views

### Behaviour of first $l^2$-Betti number under quotienting

Let $G$ be a finitely generated group, and let $H = G / N$ be a quotient of it. We have two observations:
1) In general, it is $\textbf{not}$ true that $\beta_1^{(2)}(G) = 0 \Rightarrow ...

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71 views

### Is it a correct description of the bounded above derived category of coherent sheaves?

Let $X$ be a (Noetherian) scheme. Let $D^{-}_{\text{coh}}(X)$ be the derived category of complexes of $\mathcal{O}_X$-modules with bounded above and coherent cohomologies.
Do we have the following ...

**2**

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44 views

### $t$-analogue of the symmetric power of an additive character over $\Bbb{F}_q^*$

Let $G$ be a finite group and let $f: G \longrightarrow \Bbb{C}$ be any complex-valued function. For integers $k, n \geq 0$, an indeterminant $t$, and $x \in G$ let $f_k(x) := f \big( x^k \big)$ and ...

**6**

votes

**1**answer

67 views

### On a permutation module for GL(n,q)

Let $G=GL(n,q)$ be the general linear group of degree $n$ over the $q$ element field. Let $X$ be the set of full rank $n\times r$ matrices where $1\leq r\leq n$. Then $G$ acts transitively on the ...

**8**

votes

**3**answers

492 views

### “Epicycles” (Ptolemy style) in math theory?

By analogy:
The epicycles of Ptolemy explained the known facts in the sun system and in this sense were not "wrong". But they distracted from a better insight. From another viewpoint, everything fell ...

**2**

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160 views

### When is the category of small (pre)sheaves a(n elementary) topos?

When $C$ is essentially small, the presheaf category $[C^\mathrm{op},\mathsf{Set}]$ is the free cocompletion of $C$. The presheaf category $[C^\mathrm{op},\mathsf{Set}]$ is also a topos.
When $C$ is ...

**3**

votes

**1**answer

33 views

### Rate of convergence of Bayesian posterior

Suppose a data generating process (DGP) is parameterized by some unknown parameter $\theta_0$, say $P_{\theta_0}$, and we want to estimate the value of $\theta_0$ using Bayesian method. Let ...

**5**

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36 views

### A “lower-central” filtration of Steenrod algebra?

$\renewcommand{\Atwo}{\mathcal{A}_2}$ So, a lot of good work has been accomplished by filtering the Steenrod algebras $\mathcal{A}_p$ in powers of the Augmentation ideal; For reasons partly ...

**5**

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**1**answer

78 views

### Singular/Smooth locus of Schubert variety of the affine grassmannian

Let $G$ be a connected, simply connected, semisimple, complex linear algebraic group with maximal torus $T$ and affine Grassmannian $\mathcal Gr$. It is well known that $\mathcal Gr$ admits a Bruhat ...

**4**

votes

**2**answers

115 views

### Combinatorial identity and Fuss-Catalan numbers

I would like to show that
$$
\lim_{N\to\infty}\frac{1}{N^{np+1}}\frac1{p!}\sum_{j=0}^{p-1}(-1)^j\binom{p-1}{j}
\left(\frac{\Gamma(N+p-j)}{\Gamma(N-j)}\right)^{n+1}
=\frac1{np+1}\binom{(n+1)p}{p},
$$
...

**2**

votes

**2**answers

149 views

### Applications of Szemeredi's Theorem

Szemeredi's Theorem is a famous theorem in Additive Combinatorics, Ergodic Theory and maybe some other parts of Mathemtaitcs:
(Szemeredi's Theorem) Let $\Lambda \in \mathbb{Z}$ be a subset of ...

**0**

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**0**answers

54 views

### Refomulation of a theorem for special case

This question is about some theorems in the book "Analysis Now" from Pedersen.
In particular Proposition $5.3.2$ and Theorem $5.3.3$. Here one has a essential $*$-isomorphism of some algebra $L(X)$ ...

**1**

vote

**1**answer

91 views

### Dieudonné modules -reference request

I need a reference to start learning about Dieudonn\'e modules, and their application to the arithmetic of abelian varieities. I know that this is a copy of Reference for Dieudonné modules, ...

**0**

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**0**answers

24 views

### Finite element method p2 2d [on hold]

I'm preparing my graduate project and i really need some help to implement FEM 2D with quadratic element triangles, so i have done everything so far and i think the problem is in the assembling of the ...

**9**

votes

**2**answers

398 views

### Consecutive numbers with mutually distinct exponents in their canonical prime factorization

Is it possible to find 23 consecutive positive integers each of which has mutually distinct exponents in its canonical prime factorization? Such numbers are sequence A130091 in OEIS. 24 such numbers ...

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vote

**1**answer

35 views

### Decomposing large symmetric banded sparse matrices

I'm investigating 3D image deblurring and one of the approaches I'm interested in is applying spatial regularisation. To do this I have generated a matrix $A$ which encodes the 6-connectivity of each ...

**5**

votes

**0**answers

59 views

### Max min of functionals

I have an interesting question which I believe was probably already studied, but I could not find anything. Let $n, m \geq 1$ be fixed. Suppose that $|| \cdot ||$ is a norm in $\mathbb{R}^n$ and $f_1, ...

**4**

votes

**2**answers

67 views

### Finding joint probability from double marginals

Consider three probability distributions in the form $p_1(y,z),p_2(x,z),p_3(x,y)$.
When does a global joint probability $p(x,y,z)$ (possibly not unique) exist?
The first compatibility condition to ...

**2**

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**0**answers

94 views

### Embeddings of subshifts

Consider $(X,\sigma_X)$ and $(Y, \sigma_{Y})$ be subshifts of the one sided shift in two symbols. Assume that $(X,\sigma_X)$ is a transitive subshift of finite type and $(Y, \sigma_{Y})$ is a ...

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34 views

### How can I calculate the global log canonical threshold?

Let $X$ be a normal variety and let $D$ be a $\mathbb{Q}$-divisor. The log canonical threshold of a pair $(X,D)$ is
$lct(X,D)=sup\{c|(X,cD)$ is log canonical$\}$.
If $X$ is $\mathbb{Q}$-Fano ...

**4**

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118 views

### A strange condition on containment of special complex numbers in cyclotomic fields

In a recent theorem we have naturally come across this condition, that seems to be important, but rarely satisfied:
$\sqrt{\frac 1 4 + a^m} \in \mathbb Q(\zeta_m, a)$
where $a\in\mathbb C^*$ and ...

**3**

votes

**1**answer

103 views

### Is there a maximal connected Hausdorff space?

We call a space $(X,\tau)$ maximal connected, if it is connected, and for any topology $\sigma \supseteq \tau$ with $\sigma\neq \tau$, the space $(X,\sigma)$ is not connected.
Is there a maximal ...

**1**

vote

**1**answer

72 views

### Maximal connected topologies

We call a space $(X,\tau)$ maximal connected, if it is connected, and for any topology $\sigma \supseteq \tau$ with $\sigma\neq \tau$, the space $(X,\sigma)$ is not connected.
If $(X,\tau)$ is ...

**0**

votes

**1**answer

34 views

### Defining a brownian bridge indexed by angle

I have a random closed curve of the form $(\theta,r_\theta)$, where $\theta\in [0,2\pi]$, is the counter clockwise angle from the x-axis and $r_\theta$ is the radial distance from the origin ...

**-5**

votes

**0**answers

19 views

### LyX preamble to auto add space before and after math (CTRL+M) [migrated]

I tried everything, but nothing works.
How can I make auto space bofore and after math formulas in the same line?
Thank you.

**3**

votes

**1**answer

55 views

### Null tetrad transformation

I have been going through the Chandrasekhar's "The Mathematical Theory of Black holes", in particular the chapter on Newman Penrose formalism.
I have a question about what he calls a "class III ...

**1**

vote

**0**answers

75 views

### Irreducibility of a general fibre

Let $A\subseteq B$ be an inclusion of affine domains over an algebraically closed field $k$ of characteristic $0$. Can someone give me a reference for the following fact?
If $A$ is algebraically ...

**4**

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**0**answers

74 views

### Relating different topologies on $C^{\infty}_c(M)$

This is somehow connected to this question.
I can think of at least four topologies to put on $C_c(M)$:
Topologize $C^{\infty}_c(M)\subseteq C^{\infty}(M)$ as a subspace with the weak Whitney ...