# All Questions

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### How to calculcate frecency? [on hold]

I recently came across the concept of Frecency. I thought it was a typo, but apparently it's a combination of recency and frequency, used in Mozilla's URL bar. What are possible formulas for ...
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### edge transitivity and edge deletion

Let G be a graph which has the following properties: 1) For every $e_1,e_2 \notin E(G)$, $G \cup e_1 \cong G \cup e_2$ 2) For every $e_1,e_2 \in E(G)$, $G\setminus e_1 \cong G\setminus e_2$ i.e. ...
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### Maximal subgroups of indefinite special orthogonal group SO(p,q)

Can someone answer the following question: Is there any classification of maximal proper Zariski-closed real subgroups of $SO(p,q)$ which are not parabolic, and satisfy the following conditions: ...
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### Square filling self avoiding walk

I want to create an algorithm that fills a square grid with a random Hamiltonian path starting at a particular point. See this example. One approach is to try a free direction as a next step, and ...
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### Learning roadmap in Algebra [on hold]

I am a senior undergraduate student in mathematics, I have a sound knowledge in the following areas: a) Commutative Algebra b) Field Theory and Galois Theory c) Homological Algebra My question is ...
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### Expanding graphs from iterated zig-zag product

Let $\Gamma \, zz\, G$ denote the zig-zag product of graphs $\Gamma$ and $G$. Reingold, Vadhan, and Wigderson proved that the second largest eigenvalue of the normalized adjacency matrix of the ...
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### How can I prove: If A is a subset of C and B is a subset of D, then the union of A and B is a subset of the union of C and D? [on hold]

How could I write a proof for the above statement, considering I'm studyng the first Enginnering math's course? (in other words, my math level is pretty basic) Thanks in advance
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### How many simultaneous polynomial equations of degree 2 can software solve today?

Consider the following problem: Input: $n$ polynomial equations of degree $2$ in approximately $n$ variables. Each equation contains about $\sqrt{n}$ monomials. We would like to find one ...
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### Convergence of complex series that are not absolutely convergent?

Does anyone know of a convergence test for a complex series of the form $$\sum_n a_n \cdot \exp(i \cdot b_n)$$ ? The particular series I need to understand has a_n going to zero as n goes ...
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### Expression and growth bound for $r_{p^m,k}(n)$

Let's define , $$R_{p^m,k}(n)=\#\{(a_1,\dots,a_k)\in\mathbb{Z}^k:\sum_{i=1}^ka_i^2\le n \ \text{and} \ p^m|\sum_{i=1}^ka_i^2\}$$ what will be growth bound of $R_{p^m,k}(n)$? This can be thought as a ...
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### Inequality due to Siegel (assumptions) and upper bounds on number field discriminants

In Siegel's 1969 paper, Abschätzung von Einheiten, on page 73, he states the inequality $$\log\sqrt d\le n-1+{n\over 2}\log\pi+r_2\log 2\qquad (*)$$ and compares with the bound due to Minkowski that ...
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### Bounding the absolute value of a polynomial involving a Diophantine equation

Let $\mathbf{z}\in\mathbb{C}^n$ with entries $z_1,z_2,\ldots,z_n$. I would like to bound the following quantity \begin{equation*} ...
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### Proof that $\sqrt2$ is irrational [on hold]

Question: Using fundamental theorem of integers and the fact that every natural number that is not prime, prove that $\sqrt{2}$ is irrational unless $n=m^2$ for some $m\in\mathbb N$. Here is how I ...
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### Number of solutions in a sum of squares Diophantine equation

Let $n$ be an integer. I'm interested in upper bounding the number of integer solutions of \begin{equation*} x_1^2+x_2^2+\ldots+x_p^2=y_1^2+y_2^2+\ldots+y_p^2, \end{equation*} where for all ...
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### u-Invariants of p-adic function fields

In his Paper "Fields of u-invariant 9" Oleg Izhboldin points out that for a algebraic closed, finitely generated field $k$ we have $u(k)= 2^{cd(k)}$. In particular we have ...
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### Studying Signal Processing [on hold]

I'd Like to ask two questions : What is the difference between studying Signal processing (both Deterministic and statistical) in Department of Electrical Engineering versus Department of Mathematics ...
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### Proof that at least one of the nontrivial zeta zeroes has an irrational height (assuming RH) [on hold]

This seems quite simple so its likely someone has done this before (a few Google searches returned empty and I would be really grateful for a relevant link), but in case it's new, I wanted to check if ...
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### Rank one (phi,Gamma)-modules

Let $\mathbb{Q}_p$ be the field of $p$-adic numbers. Consider an unramified representation $\rho : Gal(\bar{\mathbb{Q}}_p / \mathbb{Q}_p) \to \mathbb{F}_p^{\times}$ which sends the arithmetic ...
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### Continuous extension of Riemann maps and the Caratheodory-Torhorst Theorem

If $G\subsetneq\mathbb{C}$ is a simply-connected plane domain, then by the Riemann mapping theorem there is a conformal isomorphism $\newcommand{\D}{\mathbb{D}}\varphi:\D\to G$, where $\D$ is the unit ...
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### Diagonally change the matrix [on hold]

if we have a matrix 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 then we have to change the elements diagonally from top left to bottom right ? what it ...
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### Finding a smooth 6-manifold with a closed 2-form which is degenerate only along some embedded 2-spheres

Given a symplectic 6-manifold $(M,\omega)$ and an embedded symplectic 2-sphere $C\subset M$ whose normal bundle has the first Chern class -2. How to find on $M$ another closed 2-form $\eta$ which only ...
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### A bound on the size of the center

Let $p$ be a prime number, $F$ a free pro-$p$ group, $H \leq_c F$ of infinite index. Can it be that $$\sup_{N \lhd_o F} |Z((F/N)/C_{F/N}(HN/N))| < \infty ?$$
### Reference for finite number of Weyl groups of reductive groups of rank $r$
Dear Mathoverflowers, I am interested in the following pde: $$-\Delta u(x) + C(x) u(x) = 0$$ in $R^N$. Lets assume that $C(x)$ is bounded and (smooth if you like) and satisfies the ...