# All Questions

**2**

votes

**1**answer

42 views

### Solving complicated equation involving integral of error functions

I've been trying to solve the following equation for $\sigma$
$$\sigma^2 = \int_0^1 \left\{ \frac{1}{2} \operatorname{erfc} \left[ \frac{x + B}{\sqrt{2 (Rp - 1)} \, \sigma} \right] + \frac{1}{2} ...

**0**

votes

**0**answers

34 views

### Centralizer of a non-regular Lie algebra element

It is well understood that the centralizer of a regular element $A$ of a Lie algebra of complex (square, diagonalizable) matrices consists of polynomials $p(A)$ in that element of degree less than $n$ ...

**2**

votes

**0**answers

29 views

### Comparing right and left quasi-representable bimodules

Let $\mathcal V$ be your favourite (closed, symmetric) monoidal model category. To fix ideas, set $\mathcal V = \mathrm{Ch}(k)$, the category of chain complexes over a fixed commutative ring. Given a ...

**1**

vote

**0**answers

44 views

### Nonlinear Schrödinger blow-up for non radial solutions

I am studying a paper of Frank Merle and Pierre Raphaël,
http://math.unice.fr/~praphael/Publications/blow-up-norme-critique.pdf.
The equations are
$$
i\partial_tu+\Delta u=-|u|^{p-1}u
$$
on ...

**-1**

votes

**0**answers

109 views

### Which classes of geometric results or problems can not be achieved by algebraic methods [on hold]

Algebra has been using when necessary as a tool to solve geometric and topological problems. I have seen algebraic results through geometric methods in the literature. Which classes of geometric and ...

**-2**

votes

**0**answers

49 views

### Can someone help me with a Towers of Hanoi problem? [on hold]

I have 9 disks which is hard to keep track of, and I want to know... out of the 2^9 -1 moves... how many positions are there when all three posts are occupied, and is there a short formula describing ...

**0**

votes

**0**answers

15 views

### question about lambda calculus [migrated]

I'm triyng to understanding lambda calculus but I have some difficulty espacially when websites or books I search starts to make things a bit more complicated.
what I've understood by now is:
given
...

**-1**

votes

**0**answers

60 views

### Lemma: (Path -Cantor Lifting)? [on hold]

Definition: Let $p:E\rightarrow B$ be a map. If
$f:X\rightarrow B$is a map, a lifting of is a map
$\widetilde{f}:X\rightarrow E$ such that $p\circ \widetilde{f}=f$
¿TRUE or FALSE?
"Let $C$= Cantor ...

**7**

votes

**2**answers

161 views

### approximate two different real numbers to order $\frac{1}{z^{3/2}}$

I took this result from Minkowski's book on Geometry of numbers:
Two arbitrary real quantitites $a$ and $b$ may be made to approach as near as we wish in value the two fractions $\frac{x}{z}$ and ...

**2**

votes

**1**answer

186 views

### Which base change preserves integrality of schemes

Let $f:X \to Y$ be a flat morphism of projective noetherian integral schemes. Is there any known condition on a morphism $Z \to Y$ under which the resulting fiber product $X \times_Y Z$ is still ...

**1**

vote

**0**answers

113 views

### algebraic closedness in in residue field [on hold]

If $A\subseteq B$ are affine domains over an algebraically closed field of $k$ of characteristic zero, such that $Q(A)$ is algebraically closed in $Q(B)$, how can one show that $Q(A)$ is also ...

**0**

votes

**1**answer

123 views

### irreducibility of general fiber

I would like to get a reference of the following fact.
Let $A\subseteq B$ be affine domains over an algebraically closed field of characteristic zero. If $Q(A)$ is algebraically closed in $Q(B)$, ...

**-2**

votes

**0**answers

62 views

### Fractal Generators and Symmetry [on hold]

Using the Mandelbrot set as a starting place, $z_{n+1} = z_n^2+c$, may be written and computed as:
$x_{n+1} = x_n^2 -y_n^2+Re(c)$
$y_{n+1} = 2.0*x_n*y_n+Im(c)$
Let f(x,y) and g(x,y) be ...

**0**

votes

**0**answers

47 views

### On the centroid of a triangle [migrated]

There's three different ways to see a triangle in the Euclidean plane:
as three non-collinear points, say $A$, $B$, $C$;
as the line segments connecting the three points, that we can parametrize as a ...

**2**

votes

**2**answers

46 views

### Animating a unitary transform [on hold]

For the purpose of showing how (quantum) unitary operators behave as a computer animation, I would like to create a function $A_U(t)$ of some (complex) unitary matrix $U$, such that $A_U(t)$ is ...

**0**

votes

**0**answers

49 views

### About equivalence of two fractional Sobolev/Hilbert spaces

Let $(\varphi_k, \lambda_k)$ be the eigenelements of the Neumann Laplacian. It's possible to define a space
$$H(\Omega) = \{ u \in L^2(\Omega) \mid \sum_{k \geq 1}\lambda_k^{\frac ...

**4**

votes

**0**answers

77 views

### behaviour of first eigenfunction near the boundary

Consider $\Omega$ a smooth bounded domain in $R^N$ and suppose $ \phi_1(x)>0$ is the first eigenfunction of $ -\Delta$ in $H_0^1(\Omega)$ normalized however one chooses.
My interest is in how $ ...

**4**

votes

**1**answer

134 views

### How to teach generalizing the induction hypothesis? [on hold]

I just finished teaching a class on using proof assistants (in this case, Agda) to write provably correct programs. Reflecting on how it went, the biggest difficulty I noticed the students having was ...

**0**

votes

**0**answers

49 views

### Restriction of locally free sheaves and semi-stability on curves

Let $C$ be a stable curve and $\mathcal{F}$ be a locally free sheaf on $C$ such that the restriction of $\mathcal{F}$ to any of the irreducible component $C_i$ of $C$, $\mathcal{F}|_{C_i}$ is Gieseker ...

**4**

votes

**1**answer

105 views

### Multivariable function analysis

Sorry if the terms I'm going to use is not professional enough:) This is about the complexity analysis of an algorithm.
Let $\alpha$ be the largest zero root of the polynomial ...

**1**

vote

**0**answers

191 views

### Analogues of the Monster for central charges different from 24

One way to define the Monster group is to consider a conformal field theory (CFT) corresponding to central charge $c=24$ and look at the automorphism group of its vertex operator algebra. For one of ...

**0**

votes

**0**answers

30 views

### the associated action on the transition functions

Let $X$ be a curve with an involution $\sigma$ generically unramified, given a $G-$bundle $E$ of rank $r$, than we ca take its pull-back, I want to describe the action of $\sigma$ on $G$. Fix a ...

**1**

vote

**0**answers

49 views

### Probabilistic proof for expander existence [on hold]

I am new to probabilistic proofs and trying to understand them better. Apparently, a common probabilistic proof focuses on the existence of expanders (eg. vertex expanders).
I've been using the search ...

**4**

votes

**0**answers

93 views

### Rellich's theorem from compact resolvent

On a compact Riemannian manifold, we know that the Laplacian $\Delta$ has compact resolvent. In proving this, one typical way is to use Rellich's theorem about the compact embedding of $H^1(M)$ into ...

**0**

votes

**0**answers

23 views

### rank of a Lie group over a non-archimedean local field of positive characteristic

In the case of a Lie algebra over a non-archimedean local field of positive characteristic (I have been led to believe that) it is not necessarily true that all Cartan subalgebras have the same ...

**0**

votes

**0**answers

50 views

### Titchmarsh S function [on hold]

SO it is known that Titchmarsh S function $$ S(T)= \pi^{-1} arg\quad \zeta\bigg(\frac{1}{2}+iT\bigg)$$ under the assumption of riemann-hypothesis gives $$ S(T)=O(\frac{\log T}{\log \log T})$$ can ...

**2**

votes

**0**answers

74 views

### Does every group that satisfies the maximal permutizer condition then satisfy the permutizer condition?

The
permutizer of a subgroup $H$ of $G$ is defined to be the subgroup generated by all cyclic subgroups of $G$ that permute with $H$,
i.e. $\langle x \in G | \langle x \rangle H = H \langle x \rangle ...

**1**

vote

**0**answers

17 views

### LU growth factor applied to LDL of a Positive Semidefinite matrix [on hold]

For a Positive Semidefinite matrix $A$, which we can decompose through $LDL$ decomposition as follows: $A=LDL^\text{T}$; how can we prove that for a decomposition $A=LU=L(DL^\text{T})$, the growth ...

**0**

votes

**0**answers

109 views

+50

### Local coordinates on (infinite dimensional) Lie groups, factorization of Rieman zeta functions

Given a (finite dimensional) Lie group $G$ (real $k=\mathbb{R}$ or complex $k=\mathbb{C}$) and its Lie algebra $\mathfrak{g}$, one can prove (a basis $B=(b_i)_{1\leq i\leq n}$ of $\mathfrak{g}$ being ...

**0**

votes

**0**answers

43 views

### Does this count as a canonical decomposition for non-elementary hyperbolic 3-orbifolds?

Let $\Gamma$ be a Kleinian group and let $\mathbb{H}^3$ be the upper half-space model for hyperbolic 3-space.
Then $\mathbb{H}^3/\Gamma$ is an orientable hyperbolic 3-orbifold (with the group action ...

**9**

votes

**1**answer

304 views

### What are the strongest conjectured uniform versions of Serre's Open Image Theorem?

This question concerns the uniform conjectured effective versions and generalizations of these two results of Serre on $\ell$-adic Galois representations $\rho_{E,\ell}$ associated to a non-CM ...

**1**

vote

**0**answers

128 views

### Surgery to unlink $S^p$ and $S^q$ in $S^d$

We know that $S^p$ and $S^q$ can be linked in $S^d$ if $p+q<d$. Let us consider the simplest case where both $S^p$ and $S^q$ are un-knotted spheres.
I am looking for a surgery to unlink $S^p$ and ...

**-1**

votes

**0**answers

56 views

### Difficult examples of invertible differentiable functions [on hold]

Give an example of:
1)$f:\mathbb R^2 \to \mathbb R^2$ such that $f$ is invertible in some neighbourhood of $x_0$ (that is $f$ is locally invertible) but $|Jf(x)|=0$ (jacobian determinant) $\forall x$ ...

**-4**

votes

**0**answers

28 views

### Finding kernel and image [on hold]

X ={(x1,x2,x2 −x1,3x2):x1,x2 ∈R}
f(x1,x2,x2 −x1,3x2)=(x1,x1,0,3x1)
What is the dimension of X?
Find ker f and im f.
Find bases for ker f and im f.
Is f a bijection?
My attempt:
1. I calculate dim ...

**4**

votes

**0**answers

97 views

### Minimum number of real multiplications to multiply two quaternions [on hold]

Karatsuba multiplication of two complex numbers can be performed with just three real multiplications (instead of four) as follows:
$$(a+bi)(c+di) = (ac-bd) + i ((a+b)(c+d) - ac-bd)$$
We only need the ...

**0**

votes

**0**answers

76 views

### Can someone help me find a Mathematical documentary that aired on British television within the past 10 years about Leibniz? [on hold]

I have been searching for a documentary that aired on British television between around 2006 and 2012 which was centred around the German Mathematician, Gottfried Leibniz. All that I can remember ...

**0**

votes

**0**answers

64 views

### Alternate proof for Caratheodory extension theorem

This question is on the intuition behind the Caratheodory definition of measurable sets as given in Billingsley. He motivates by saying that we "should" call a set $A$ measurable if $$P^*(A) + ...

**1**

vote

**0**answers

116 views

### Two spaces attached to mod 2 level 9 modular forms--a conjectural Hecke isomorphism

MOTIVATION
Nicolas and Serre have analyzed the structure of the space of mod $2$ modular forms of level $1$, viewed as a "Hecke-module". They show that for each $p>2$, the operator $T_p$ acting on ...

**0**

votes

**0**answers

51 views

### Contraction with a vector field and pullback bundle

While trying to understand the proof of "smooth" version of Kostant-Hochschild-Rosenberg theorem (which is due to Connes for compact smooth manifolds) I found the following argumentation: one is ...

**0**

votes

**0**answers

61 views

### Elliptic Curve: Q=nP [on hold]

I have a question relating to Elliptic Curve Scalar Multiplication between two points. Given two points on that curve, Q and P, where Q=nP, is it possible to find n if we have an m such that mQ=P?

**6**

votes

**1**answer

85 views

### Does a Gaussian process shrink under a contraction map

Let $T \subset \mathbb R^n$, and assume it's a finite set if that helps. Consider the symmetric Gaussian process $(X_t)_{t\in T}$ defined by $X_t = \langle G, t\rangle$, where $G$ is a standard ...

**3**

votes

**1**answer

117 views

### A question of terminology regarding integer partitions

I am wondering if there is a standard notation and name for the following. Let $\lambda$ be a partition $\lambda_1\geq \lambda_2\geq\cdots\geq \lambda_r\geq 1$ of $n$ into $r$ parts. Then we can ...

**0**

votes

**0**answers

112 views

### Is there any computation of $K^0(X)$ and $K_0(X)$ for a singular curve $X$?

Let $X$ be a projective curve over an algebraic closed field $k$ which characteristic zero. Define $K^0(X)$ as the Grothendieck group of the derived category $Perf(X)$ and $K_0(X)$ as the Grothendieck ...

**1**

vote

**0**answers

73 views

### Syzygies in integral domains

Let $f$ be a homogeneous irreducible element in a graded commutative Noetherian ring.
What is the possible set of elements $f_1$ and $f_2$ such that $f=f_1g_1+ f_2g_2$?
Even in very particular cases ...

**2**

votes

**2**answers

89 views

### Variation of Hodge structures associated to a hermitian symmetric domain

Let $D$ be an irreducible hermitian symmetric domain. Then there exists a variation of Hodge structures $(h_s)_{s\in D}$ on a vector space $V$ satisfying specific conditions which depend on $D$ such ...

**5**

votes

**1**answer

107 views

### Bounding the number of lattice points inside an $n$-dimensional ellipsoid

I am wondering if it is possible to produce an upper and/or lower bound on the number of integer lattice points that lie inside an $n$-dimensional ellipse.
That is, given an $n$-dimensional ellipsoid ...

**3**

votes

**4**answers

195 views

### Uniform upper bound for the sum over primes $\sum_{p \leq x} p^{-1+\varepsilon}$

I am reading the article D. M. Gordon and C. Pomerance, The distribution of Lucas and elliptic pseudoprime, Math. Comp. (1991) (click).
In equation (27) the authors, apparently, used the following ...

**18**

votes

**1**answer

345 views

### Can topological cyclic homology compute Picard groups?

Let $K$ be a number field, and $\mathcal{O}_K$ its ring of integers. Then there is an isomorphism
$$K_0(\mathcal{O}_K) \cong \mathbb{Z} \oplus Pic(\mathcal{O}_K)$$
where $Pic(\mathcal{O}_K)$ is the ...

**5**

votes

**1**answer

165 views

### An unusual metric reconstruction problem

$\newcommand{\bR}{\mathbb{R}}\newcommand{\pa}{\partial}$This questions has some nebulous roots in Morse theory. The most general version goes as follows. Fix an integer $n\geq 2$. Suppose that we have ...

**-3**

votes

**0**answers

41 views

### Calculate Inverse Fourier Transform [on hold]

How to calculate the Inverse Fourier Transform of the following functions:
$\dfrac{1}{-1+2\pi i x}$
$\dfrac{1}{(2\pi ix)^2-2 \pi ix +1}$
I don't know how to evaluate the integrals.