# All Questions

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### Fano varieties of cubic threefolds

Let $X$ be a smooth cubic threefold over $\mathbb{C}$. Let $F(X)$ denote the Fano variety of lines in $X$, which is a smooth surface of general type. Is this class of surfaces distingushed ...
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### The Riemann Zeta Function Works [on hold]

1 - Any counterexamples known for the Riemann Zeta Function? 2 - How to generalize the following? Here we have the visualization of the Riemann Zeta Function 3D Plot and the plane. We can observe ...
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### Can this specific Mixed-Integer Linear Program constraint be expressed? [on hold]

Thanks for your time. I have a linear program and no idea how I could express a form of constraint and even if it's possible. Maybe someone here know a solution. A company assembly and sells a ...
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### The number of blocks in Szemerédi Regularity Lemma

In mathematics, the Szemerédi regularity lemma states that every large enough graph can be divided into subsets of about the same size so that the edges between different subsets behave almost ...
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### Resolving nodes of a quintic CY 3-fold

Let's consider the following quintic 3-fold $X$: $$\{(x_i) \in \mathbb{P}^4 \ | \ x_1f(x)-x_2g(x)=0\}$$ for generic homogeneous polynomials $f(x),g(x)$ of degree four. It ...
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### Understanding Prof. Keevash's proof on the “Existence of Designs” [on hold]

I have tried to read Prof. Kevvash's paper on the "Existence of designs". I am finding it very tough to read it linearly. I am comfortable with the nibble ideas and probabilistic methods in general. ...
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### the eigenvalues of a generalized circulant matrix

A $2k\times 2k$ circulant matrix $\ C$ takes the form \begin{align} C= \begin{bmatrix} c_0 & c_{2k-1} & \dots & c_{2} & c_{1} \\ c_{1} & c_0 & c_{2k-1} & & c_{2} ...
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### Behavior of elementary symmetric polynomials near zero sets

It is straightforward to show (see Characterizing intersection of zero sets of elementary symmetric polynomials on R^n) that the set of points $\Lambda_{k}$ in $x \in \mathbb{R}^{n}$ with ...
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### Compare time it takes to travel a curve and a line [on hold]

First posted in Math Stack Exchange: http://math.stackexchange.com/questions/989690/compare-time-it-takes-to-travel-a-curve-and-a-line?noredirect=1#comment2025799_989690 Suppose you have a right ...
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### Polynomial recurrence relation covering the integers (and then Gaussian integers)

Say that a polynomial recurrence relation (my terminology) for $f_i$ is: $k$ initial conditions setting $f_1,\ldots,f_k$ to integers ($\in \mathbb{Z})$. A recurrence equation of the form $f_i =$ a ...
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### Number of orbits of $\mathrm{SL}_2(\mathcal O_A)$ on $\mathbf P^1(A)$ when $A$ is a quaternion algebra

This is a reference request. Let $A$ be an anisotropic quaternion algebra over $\mathbf Q$. Let $\mathcal O_A$ be a maximal order in $A$. Then $\mathrm{SL}_2(A)$ acts transitively on the right on ...
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### What is the state of art MIQP solver

I used Gurobi with a MIQP with 26 binary variables and 26*4 interaction term without any other constraint. The speed is very slow already.... I want to ask what is the state of art of MIQP solvers. ...
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### Intersection points of closed curves inscribed in a convex polygon

Suppose that I have two distinct simple closed curves, $C_1$ & $C_2$, and each is inscribed in a convex polygon, D. By inscribed, I mean tangent to each side of D. In particular, I am most ...
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### Arranging books into bags [on hold]

I'm trying to find an algorithm to answer the following question (informal): given a (finite) set of distinct books of different (positive integer) sizes and a (finite) set of bags of different ...
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### In Dedekind' construction of real numbers, what's wrong with this understanding [on hold]

in this prove, every cut corresponds to a real number. and a cut is a subset of Q.and cut have these three properties.1.is not empty 2.if p belong to this cut,any qp so in my understanding, every cut ...
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### transitive actions of automorphism group [on hold]

Can a finite group be extended to a group whose group of automorphisms acts transitively on the first group. Or more generally, given any finite module, can we extend this module so that the group ...
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### How to solve $e^{f(x)} + a f(x) + bx = 0$ [on hold]

How should determine solutions to equations of this form? $$e^{-f(x)} + b f(x) = ax$$ Here $f(x)>0$ is real valued. Also $a>0$, $b>0$.
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### Finite extension of K(x) with extra structure: definable over field of invariants?

Let $K$ be an algebraically closed field, and let $\sigma$ be an automorphism on $K$. Set $k=K^\sigma$. Consider the rational function field $K(x)$ and extend $\sigma$ to $K(x)$ by $\sigma(x)=x$, ...
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### How to solve the following integral [on hold]

Do you have any idea how to solve the following integral: $\int\limits_0^a {{e^{ - \frac{{by}}{{c - dy}} - ey}}dy}$, where $a$, $b$, $c$, $d$ and $e$ are constants? Thank you very much.
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### Finite series with reciprocal factorials

I asked the question at MSE http://math.stackexchange.com/questions/982388/simple-finite-series-with-reciprocal-factorials but got no answer or comment (it is not a homework). I'm trying to find the ...
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### Any counterexamples known for the Generalized Tate conjecture?

One can state the generalized Tate conjecture over arbitrary finitely generated fields; to this end one should just define Galois representation to be effective if the eignevalues of the actions of ...
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### Polynomial (non-)embedding of a simplex in euclidean space

Let $\Delta$ be a standard $k$-simplex, and let $f:\Delta\to\mathbb R^N$ be a polynomial map with known numerical coefficients. What sort of practical computational algorithms can be used to ...
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### $j$-invariants of elliptic curves over finite fields

Let $K$ be a finite field, and $\overline{K}$ its algebraic closure. It is well known that two curves are isomorphic over $\overline{K}$ if and only if they have the same $j$-invariant. If two such ...
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### Is every number the sum of two cubes modulo p where p is a prime not equal to 7?

If p is a prime other than 7, can every integer be written as sum of two cubes modulo p? Has Waring's problem mod p for cubes been proved simply and directly? Thanks for your proof. Lemi
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### Which groups are LERF?

A finitely generated group $G$ is called LERF if every finitely generated $H \leq G$ is closed in the profinite topology on $G$ (equivalently, there is a family of finite index subgroups of $G$ ...
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### 2x3 = 5+1 AND 2+3 = 5x1. How many other examples of this type? [migrated]

I noticed the following: 2x3 = 5+1. If you switch the operators, it is still true: 2+3 = 5*1. There is another obvious/trivial example where you can swap the operators: 2x2 = 2+2. I think these ...
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### Existence of half-planes with respect to regular open sets of the Euclidean plane

I initially asked this question at math.stackexchange.com but there was no reaction, so I thought this may be a good idea to transfer it to mathoverflow.net Let ...
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### When is a group Fibonacci sequence contained in a single conjugacy class?

First a definition: a Fibonacci sequence in a group is a sequence in which the first two elements may be arbitrary, and from there on each element is a product (using the group operation) of the ...