# All Questions

**-1**

votes

**0**answers

11 views

### How do you generate orthogonal Rotations in d-dimensions?

I know that matrices that satisfy $\mathbf{x^TMx} > 0$ for all $\mathbf{x} \in \mathbb{R}^d$ are called positive definite matrices.
It seems to me that a matrix that represents an $90^{\circ}$ ...

**0**

votes

**0**answers

10 views

### Realizing algebraic curves as complete intersections

I have two related questions about smooth complete algebraic curves (over $\mathbb{C}$).
Does there exist a smooth complete algebraic curve $X$ that cannot be embedded as a complete intersection in ...

**-2**

votes

**0**answers

31 views

### Map from real numbers to real numbers as abelian groups [on hold]

What is an example of an abelian group homomorphism from $\mathbb{R}$ to $\mathbb{R}$ that is NOT a linear transformation?

**3**

votes

**0**answers

31 views

### reference on aperiodicity and cluster

From this image:
I believe there is a message relating those clusters drawn in picture and aperiodic tiling. Does anyone have some reference on this? Thank you:)

**2**

votes

**1**answer

64 views

### Proof of the Dunford-Pettis theorem

I would like to know where to find a complete proof of the Dunford-Pettis theorem:
A sequence $(f_n)_{n\geq 0} \subset L^1$ is uniformly integrable if and only if it is relatively compact for the weak ...

**1**

vote

**1**answer

40 views

### Software producing complex trees

Does anyone know any kind of graph software that could produce graphs like this for publication? Those links and crosses and numbers actually needs to be presented…. Thank you:)
One small update, ...

**0**

votes

**0**answers

51 views

### How to find generators to Mordell weil groups of elliptic curves using Sage software? [on hold]

I am new to sage.I want to find generators to Mordell Weil group of the Elliptic Curve $y^2=x^3-6321363052$. While using sage it gives error as increase decent and then make use of same command but I ...

**-1**

votes

**0**answers

46 views

### Complex conjugation of positive roots

I have a simple question about root systems. Suppose that $G$ is a connected reductive group over the reals $\mathbb{R}$, and $T\subset G$ is a maximal torus (by this I mean that $T_{\mathbb{C}}$ is a ...

**0**

votes

**0**answers

23 views

### Behavior of the integral of products of probability densities

Assume $z \in \mathbb{R}^m$ and $x \in \mathbb{R}^n$. Assume we have proper density function $P(z)$ and proper conditional density function $P(x|z)$. We give the definition
$$
T(x_1,\ldots,x_n) := ...

**6**

votes

**1**answer

269 views

### Why is the section conjecture important?

As in the title, I want to know the reason for importance of the section conjecture. Of course, the statement of conjecture is important as itself, even I cannot fully grasp the soul of it. However, ...

**0**

votes

**0**answers

27 views

### Homotopy addition theorem and lifting in a certain diagram

If I am confusing somewhere here, please excuse me and ask me to clarify. The proof I am having trouble with is lemma 1.19 of Goerss-Jardine, pg. 398. I have tried to isolate the troublesome ...

**8**

votes

**1**answer

127 views

### Erdös cardinals and ineffable cardinals

In Cantor's Attic it is stated that an $\omega$-Erdös cardinal is a stationary limit of ineffable cardinals, and Jech book is given as a reference, but I cannot find this result in that book. I have ...

**6**

votes

**1**answer

73 views

### Trapping a particle

A particle starts a brownian walk in the middle of a long tunnel in the plane, at one end of the tunnel is a circular region X, at the other end a region Y of given area A.
Does the shape of region ...

**0**

votes

**1**answer

31 views

### reference request for automata's of this type

Consider the list of length $m$ $(1,0,\dots 0)$ we call this list $l_1$, we now define a sequence of lists recursively, where $l_1$ is the previous list, and if $l_n$ is the list $(a_1,a_2\dots a_n)$ ...

**1**

vote

**1**answer

47 views

### Strong maximum principle for weak solutions

Suppose I have a linear parabolic equation with solutions in the Bochner-Sobolev spaces (eg. $L^2(0,T;H^1) \cap H^1(0,T;H^{-1})$). Is it possible to obtain a strong maximum principle with a proof that ...

**3**

votes

**0**answers

37 views

### Strong convexity of the trace of the square root of a matrix function

Any clues about how to prove that the following function is strongly-concave in $x$? (We conjecture it is $2$-strongly concave but cannot prove it. We have already proved strict concavity through ...

**-3**

votes

**0**answers

28 views

### Finding Distance with Missing Coordinate Set [on hold]

I have a line that runs through the orgin with a slope of 2, with a distance of 5 from the orgin what are the coordinates and how did you solve?
I did some searching online and only found lectures on ...

**0**

votes

**0**answers

61 views

### Relation between long exact sequences and Derived functors [on hold]

I know that if i have a short exact sequence of chain complexes
$$0\rightarrow A\rightarrow B\rightarrow C\rightarrow 0$$
then i can extend it to long exact sequence of homology groups as
...

**-1**

votes

**0**answers

23 views

### impossibility and mode of convergence [on hold]

I have $\mathrm{Pr}(a>b)=0$ with $b\in[0,\infty]$, then can i have $a<0$? If this is true, which type of convergence is this?

**0**

votes

**0**answers

87 views

### Any result, example or conjecture about the computational complexity of transcendental number that can not be computed by linear time Turing Machine [on hold]

The Hartmanis-Stearns Conjecture is restated by Prof.Lipton as:
Suppose that a linear time Turing Machine computes the first $n$ digits of the real number $r$ in base ten. Then, the number is either a ...

**10**

votes

**2**answers

390 views

### Are the quaternions not uncountably categorical?

Boris Zilber has argued that the field of the complex numbers is "logically perfect". For one thing, the theory of an algebraically closed field of characteristic zero is uncountably categorical: it ...

**12**

votes

**2**answers

239 views

### Probing the generalization of the abc conjecture to more than 3 variables

Browkin and Brzezinski, in "Some remarks on the $abc$-conjecture", Math. Comp. 62 (1994), no. 206, 931–939, state the following generalization of the $abc$ conjecture to more than three variables:
...

**0**

votes

**0**answers

63 views

### Are there any relevance between coefficients of simple continued fraction of quadradic algebraic number and algebraic number with degree $2^n$ [on hold]

Let $\sqrt{c}$ be quadratic algebraic number, We know that $[a_0;a_1,a_2,\dots ]$ the coefficients of simple continued fraction of $\sqrt{c}$ the quadratic algebraic number is periodical. ...

**6**

votes

**1**answer

144 views

### Adams e-invariant

In "On the Groups J(X) - IV", Adams introduces the $e$-invariant, which turns out to be closely connected to the image of the $J$-homomorphism, but he introduces it in a more general setting. He has ...

**9**

votes

**1**answer

84 views

### Completely positive maps-equivalent definition

The most usual definition of the completely positive map (c.p.) between two C*-algebras (say, unital) is the following: $\sigma: A \to B$ should satisfy $\sigma(1)=1$ and for each $n \in \mathbb{N}$ ...

**-3**

votes

**0**answers

97 views

### Numbers half way between two primes [on hold]

Is every integer greater than 3 half way between two primes?

**1**

vote

**0**answers

113 views

### varieties whose canonical bundle has finite order in Pic?

Is there a structure theorem for such varieties?
If X is a smooth and proper/projective variety whose canonical bundle $\omega_X$ has finite order in the Picard group, do we know anything about X?
...

**8**

votes

**0**answers

106 views

### Cubic fields correspond to $3$-torsion ideals in quadratic fields, or to order $3$ characters of quadratic class groups?

I was watching Dick Gross's laudation for Manjul Bhargava, followed up by one of Bhargava's talks, and I realized I was confused about something.
Bhargava says (around 21 minutes) that the orbits of ...

**-4**

votes

**0**answers

34 views

### Adjoint quotient in terms of a Chevalley basis [on hold]

Has anyone put the adjoint quotient (of a Lie algebra) in terms of a Chevalley basis? If so, do you have a reference?

**1**

vote

**0**answers

162 views

### Quotes from Connes

I found the following remark by Connes HERE:
"the main quality of the homotopy type of a manifold is to satisfy Poincare duality not only in ordinary homology but in K-homology with the Fredholm ...

**7**

votes

**0**answers

99 views

### Can Suslin lines ever be orderings of abelian groups?

I am interested in realizing linear orders as orderings of abelian groups. In particular, can Suslin lines (and other classes of line) be realised in this way?
Let $\mathcal{C}$ be a class of ...

**9**

votes

**2**answers

317 views

### Elliptic curves with trace of Frobenius values always congruent to 0 modulo 2

Let $E/\mathbb{Q}$ be an elliptic curve and suppose that the trace of Frobenius values are such that $a_{p}(E) \equiv 0 \pmod{2}$ for all odd primes avoiding the conductor. Is it the case that $E$ ...

**8**

votes

**1**answer

159 views

### Maximum length of a chain of topologies on $\Bbb R$

Let $\frak T$ be a totally ordered set of topologies on $\Bbb R$.
Is $|\frak T|\le |\Bbb R|$?

**-4**

votes

**1**answer

175 views

### When are two algorithms essentially the same?

Inspired by Blass/Dershowitz/Gurevich's paper When are two algorithms the same? (which was referenced in another context here) I tried to boil down the question to the following situation:
Consider ...

**16**

votes

**2**answers

380 views

### construction of nonmeasurable sets

I have a history question for which I've had trouble finding a good answer.
The common story about nonmeasurable sets is that Vitali showed that one existed using the Axiom of Choice, and Lebesgue et ...

**0**

votes

**0**answers

42 views

### Conditional probabilities in epidemic model

I was contemplating an epidemic model where infection and recovery rates are determined by links. Here node $i$ is infected first and recovers at a rate $\mu_i$. For all other nodes, the recovery is ...

**0**

votes

**1**answer

100 views

### Dimension of Commutator Space

For each $n\times n$ matrix $A$ with real entries the set
$$C(A)=\{X\in M_n(\mathbb{R}): AX=XA\}$$
is obviously a linear subspace of $M_n(\mathbb{R})$.
Can we recognize the dimension of this ...

**2**

votes

**0**answers

39 views

### Image of the typenorm contains the squares

I am having a look at the paper Explicit CM-theory for level 2-structures on abelian surfaces by Bröker, Gruenewald and Lauter, and there is an argument which I don't understand. The main reason being ...

**-2**

votes

**0**answers

68 views

### Is there an example of an SDE that has no weak solution? [on hold]

So far I couldn't find an example for an SDE for which there exists no weak solution. Do you know one?

**5**

votes

**1**answer

107 views

### Tensor product of certain Sobolev spaces on non-compact manifolds

Let $M$ be a non-compact Riemannian manifold of bounded geometry (i.e., its injectivity radius is uniformly positive and the curvature tensor and all its covariant derivatives are bounded in ...

**2**

votes

**0**answers

66 views

### Existence of affine hulls

(This question is inspired by Matthieu Romagny's answer to my previous question about base change properties of affine hulls.)
Given a scheme $S$, it is well-known (cf. EGA I.9.1.21) that the ...

**-1**

votes

**1**answer

35 views

### Parallel transport along a reparametrized geodesic

Let $M$ denote a Riemannian manifold, $\gamma$ a geodesic of $M$ defined on $\mathbb{R}$. Let $t_{0} \in \mathbb{R}$ and $(\alpha,\beta) \in \mathbb{R}^{2}$. I define the reparametrized geodesic ...

**1**

vote

**0**answers

52 views

### Cover a set with balls centered at smooth functions (Ascoli theorem)

Assume $M$ to be a compact $n$-dimensional manifold, endowed with a complete metric.
Let us consider the space $C^\infty(M)$ endowed with the standard $C^\infty$ topology, i.e. generated by the ...

**4**

votes

**0**answers

81 views

### A variant of Chang's model with choice

Let $M_n$, $n < \omega$, be a models of $ZFC$ with the same ordinals, closed under countable sequences. Let $\alpha_n$ be an ordinal which is a regular cardinal in $M_n$.
Question: Is it possible ...

**-1**

votes

**0**answers

35 views

### Good Intermediate text on ODEs for self-study (meaning solved problems) [on hold]

So I am just about to finish Tenenbaum and Pollard's introductory text on ODEs and I wanted to go to the next level. I am doing this as a self-study, so I really appreciate the fact that T&P have ...

**0**

votes

**0**answers

28 views

### Properties of rearrangement maps

I have the following question to ask, concerning some properties of Schwarz radially decreasing rearrangements. It is well known that the map $u\rightarrow u^{\ast}$, being $u^{\ast}$ the Schwarz ...

**2**

votes

**1**answer

81 views

### Decay rate of the convolution of two functions

Let $f(x)=e^{-\frac{x^2}{2}}$ ($x\in\mathbb{R}$), and $g\in C^{\infty}(\mathbb{R})$ with $|g(x)|=O(e^{-k|x|^{\gamma}})$ as $|x|\to\infty$, for $k>0$, $\gamma>0$. Let $h=f*g$, the convolution of ...

**-1**

votes

**0**answers

71 views

### Sums of $n$ powers [on hold]

I managed to resolve that
$s(n) = 1^2+2^2+3^2...+n^2 = \dfrac {n(n+1)(2n+1)}{6}$ where $n$ is integer
But I'm a bit confused how to resolve:
$s(n,p) = 1^p+2^p+3^p...+n^p$ where $n$, $p$ are ...

**12**

votes

**0**answers

188 views

### Artin L-function and Zeta function of twisted Dirac operator

If one thinks of a Frobenius as an element in the fundamental group of an arithmetic curve and of a Galois representation $\sigma$ as a flat connection on the curve, then the definition of the Artin ...

**3**

votes

**0**answers

52 views

### Coloring summands of given n-partition with given weights of colors

Let $\lambda$ and $\sigma$ be n-partitions $\lambda_1+\lambda_2+\cdots+\lambda_l=n$ and $\sigma_1+\sigma_2+\cdots+\sigma_s=n$
Then let $M_{\lambda \sigma}$ be the number of ways to colour blocks of ...