3
votes
1answer
101 views
+50

Confusion about order of operations with point-in-tetrahedron formula

I am not a math student, but I am attempting to roll my own GJK-based hit detection function. It would seem that most of the Internet that I've searchedd through chooses to either ignore or obfuscate ...
0
votes
1answer
41 views
+50

Transformation Ricker equation

The classical Ricker equation for modelling density-dependent population growth is: $N_{t+1} = N_t * e^{r * \left(1-\frac{N_t}{k}\right)}$ where $N_t$ is the initial number of individuals (starting ...
3
votes
0answers
57 views
+100

mononotone and pseudomonotone operators in current research

I know that the following question is quite broad for this forum. But I am interested in references or any other ideas. Can anyone provide some examples of applications of monotone or pseudomonotone ...
5
votes
0answers
74 views
+50

Concentration of measure bounds for multivariate Gaussian distributions (fixed)

Let $\gamma_n$ denote the standard Gaussian measure on $\mathbb{R}^n$. It is known (see for example Cor 2.3 here: http://www.math.lsa.umich.edu/~barvinok/total710.pdf) that ...
10
votes
0answers
180 views
+150

Does there exist a closed form for $L_k$ for any $k>3$?

I defined a sequence $L_k$ as the limit of a sequence of "hyperharmonic" series in this question. I was surprised to find that $L_3=(\sqrt{13+4\sqrt2}-1)/2$, but was unable to find a representation ...
6
votes
1answer
145 views
+200

What's the difference between cohomology theories of varieties and topological spaces

There is defined several cohomology theories for algebraic varieties, but in the situation is very different for topological spaces (up to homotopy) for which there is only one cohomology theory for ...
1
vote
0answers
57 views
+50

Physical meaning of some identity in a weighted undirected graph

Let $G$ be an undirected graph with some weights associated with each node. Weights are normalized, sum is 1 and $w_u$ denotes the weight of node $u$. let $V(G) = C \cup \bar C $. ${\it Case }1: $ ...
8
votes
2answers
125 views
+50

Weak topologies and weak convergence - Looking for feedbacks

I am currently trying to get exactly what the weak and the weak* topologies are, in particular in connection to the concept of weak convergence in measure, however I am not completely sure on what I ...
0
votes
0answers
36 views
+50

Convention of a continued fraction presentation of a lens space

I want to clarify the following two conventions on a surgery description of a lens space. Let $p$ and $q$ are relatively prime integers. Express $$ ...
0
votes
0answers
112 views
+50

How to calculate this sum like Gauss sum.

I would like to calculate the following sum, which looks like a Gauss sum. Let $n$ be a natural number and let $a,b$ be integers. Denote by $e(x)=e^{2\pi i x/n}$. Consider the sum $$ \sum_{1 \leq j, ...
2
votes
0answers
79 views
+50

Classical perturbation theory + KAM theory

In classical canonical perturbation theory of many degrees of freedom we encounter the problem of small divisors when attempting to find a solution for the generating function of the canonical ...
2
votes
0answers
75 views
+50

Find the critical curves for the following functional

Find the critical curves for the following functional : $$J[y(x),z(x)]=\int_{0}^{1}(y'^2+z'^2-xyz'-yz)dx$$ With the conditions : $$K[y(x),z(x)]=\int_{0}^{1}(y'^2-xy'-z'^2)dx=2$$ $$y(1)=z(1)=1$$ ...
5
votes
1answer
110 views
+50

How can one find intermediate digits of a root of an algebraic equation?

I was wondering whether there is a way to find intermediate digits of an algebraic equation. For example, if I have $$234x^{\frac{1}{12345}}-24621x^{\frac{1}{3456}}=1$$ And I want to find the ...
5
votes
0answers
56 views
+150

Contraction of curves on a surface and stalks

Let $$f:X \rightarrow S$$ be a fibered surface over a Dedekind scheme of dimension $1.$ Let $$s_1, \ldots, s_n$$ be closed points of S and $\{E_{ij}\}$ irreducible vertical divisors of $X$ with ...
2
votes
3answers
60 views
+50

Conditions for uniqueness of the median

A median of a random variable is defined as any $m \in \mathbb{R}$ such that $P(X \le m) \ge 1/2$ and $P(X \ge m) \ge 1/2$. Alternatively, in terms of the CDF $F$ of $X$ defined by $F(x) := P(X ...
3
votes
1answer
99 views
+150

Techniques for proving asymptotic normality by Taylor expansion?

Suppose I have a sequence of densities $$ f_{X_n}(x) = \exp[\ell_n(x)], \qquad (x \in A). $$ My goal is to prove a statement like $\sqrt n (X_n - \mu) \to N(0, \sigma^2)$ in distribution, for an ...
13
votes
1answer
233 views
+50

Is it possible to uniquly number faces of a hexagonal grid with consecutive numbers

You have a grid of regular hexagons. The aim of the game is to have each hex contain the numbers 1-6 on its edges. Each edge must also be connected to another edge that has a value one higher and ...
3
votes
2answers
131 views
+50

A natural number $n>2$ is a prime iff $\prod_{k=1}^{n-1} k \equiv n-1 \pmod {\sum_{k=1}^{n-1} k}$

Is this proof acceptable ? Theorem 1 (Wilson). A natural number $n>1$ is a prime iff: $$(n-1)! \equiv -1 \pmod n.$$ Theorem 2. A natural number $n>2$ is a prime iff: ...
3
votes
0answers
51 views
+50

Regular sequence of sections of line bundles over a coherent sheaf

I am reading the first chapter from the book by Huybrechts and Lehn, where I encountered the following definition. I have the following doubts regarding this definition : What is the map ...
5
votes
1answer
93 views
+100

Intuition behind functional dependence

What is the intuition behind functional independence ? (This is defined in the following way: Let $k\leq n$. The $C^1$ functions $F_1,\ldots,F_k:\mathbb{R}^n\rightarrow \mathbb{R}$ are functionally ...
6
votes
0answers
146 views
+350

Ramsey (graph) theory question with tree and girth

Sorry for the abundance of questions I'm asking. Test is soon... Prove that for every tree $T$ and every $g \in \mathbb{N}$, exist $G$ with girth $g$, so that in any 2-edge-coloring of $G$ there is a ...
3
votes
1answer
103 views
+150

When does a line integral become not a line integral?

I was working thru a proof, and it changed a line integral into a normal integral. It was analogous to the below, where $\cos(\theta)\,dl=dr$ and $C$ is a path from $b$ to $a$: $$\int_C ...
22
votes
7answers
3k views
+100

How to find center of a circle from only an arbitary arc of that circle

How to find the center of a circle with given an arbitrary arc. we only have the arc nothing else. Is there any known equation or way to complete the circle.
4
votes
0answers
65 views
+50

Why a tensor product of 2x2 unitaries cannot implement a 3x3 unitary?

Let $\{v_1, \dotsc, v_m\} \in \mathbb{C}^{2^n}$ be a set of orthonormal vectors. Define a map $R_m$ from $2^n \times 2^n$ to $m \times m$ matrices as follows: $$R_m(M) := \sum_{i,j=1}^m (v_i^*M v_j) ...
11
votes
4answers
239 views
+100

Lang's Linear Algebra: what's next?

I've completed the study of Lang's Linear Algebra ($3^\text{rd}$ edition). To put it simply, I have enjoyed the subject and I would like to know "what's next". In other words, I would like to know ...
7
votes
1answer
117 views
+50

Sequences for that $\sum_{n} \frac{1}{x_n}$ is divergent and $\sum_{n} \frac{1}{x_n \ln x_n}$ is convergent

We will denote with $(x_n)$ a given sequence and we introduce the following two series. $$S^* = \sum_{n} \frac{1}{x_n} \quad \text{and} \quad S_* = \sum_{n} \frac{1}{x_n \ln x_n}.$$ We know that if ...
6
votes
0answers
114 views
+100

Approximation of the exponential

Let $c>1,k\in\mathbb{N}$. Let's consider two approximations of the exponential function : The first one is the most common one $f_k(x)=\left(1+\frac{x}{c^k}\right)^{c^k}$ and the second one is ...
1
vote
1answer
75 views
+50

I cannot make the mental leap from a vector to a function!

In my linear algebra book, it says that a vector is linearly independent if $\vec V = c1*\vec T_1 + c2*\vec T_2$ And then it goes on to say that $y(t) = c1 * e^{-at} + c2*e^{-bt}$ is linearly ...
8
votes
10answers
890 views
+50

Irrational numbers in reality

I have a square stone slab 1 metre by 1 metre, by the Pythagorean identity the diagonal from one corner to another is given by $\sqrt 2$. However $\sqrt 2$ is an irrational number, could someone ...
3
votes
0answers
77 views
+100

Expected Value of R squared

Let $n$ be a fixed positive integer. Generate $n$ numbers $x_1, x_2, ..., x_n$ from the set $[0,1]$, with the probability distribution being the uniform one and the $x_i$ all being independent of each ...
1
vote
0answers
25 views
+50

Do the maps need to be surjective in the definition of a profinite group?

Let $G_i, f_{ij}$ be an inverse system of topological groups where each $G_i$ is finite in the discrete topology. A profinite group is defined to be an inverse limit of such an inverse system. ...
2
votes
0answers
125 views
+50

Solve integral(convolution) equation

I have been trying to find a solution to the following convolution equation: \begin{align*} e^{-ax^2/2}*\ln \left(f(x)*e^{-ax^2/2}\right)+e^{-bx^2/2}*\ln \left(f(x)*e^{-bx^2/2}\right)=cx^2 ...
9
votes
1answer
98 views
+100

Geometric Interpretation of the Cross-Ratio

The cross ratio of 4 points $A,B,C,D$ in the plane is defined by $$(A,B,C,D) = \frac{AC}{AD} \frac{BD}{BC}$$ And it's a ratio which is preserved under projections, inversions and in general, by ...
2
votes
1answer
51 views
+200

Correlation of a vector generated and its one-period lag, both generated using AR(1) data

Suppose that $C_0$ is $100$ and $\{e_t\}_{t\geq 1}$ is a sequence of i.i.d. standard normal random variables. We generate $C_t=C_{t-1}+e_t$ for $t\geq 1$ and set $$ x_t=C_t^2-C^2_{t-1},\quad ...
0
votes
1answer
64 views
+50

Isometric and conformal map

We defined conformal and isometric maps for surfaces $f,g: \Omega \subset \mathbb{R}^2 \rightarrow S \subset \mathbb{R}^3$. Under a reparametrization of $f$ I understand a diffeomorphism $\Phi : M ...
3
votes
2answers
74 views
+50

Limit superior of $\sum_{j=1}^n X_j$ with $\mathbf{P}[X_j = 1] = \mathbf{P}[X_j = -1] = 0.5$

This is Exercise 2.3.1 from Achim Klenke: »Probability Theory — A Comprehensive Course«. Exercise: Let $(X_n)_{n\in N}$ be an independent family of $\mathrm{Rad}_{1/2}$ random variables (i.e., ...
4
votes
2answers
324 views
+100

Probability of some die face being missed N or more times in a row in M rolls?

Say I have a (fair) die with $F$ faces. I roll it $M$ times. How can I calculate the probability that some face was not seen for $N$ or more in a row of the $M$ rolls? (any face, not just a specific ...
5
votes
1answer
54 views
+100

Is there a generalization of the Lagrange polynomial to 3D?

What is a way to construct a smooth polynomial surface ($\mathbb{R}^2 \rightarrow \mathbb{R}$) with Lagrange-polynomial properties in every partial derivative? I want to try this for image ...
6
votes
0answers
91 views
+50

How to find the inverse arc in the configuration space

The following Figure shows the function from configuration space (Torus) to operational space (Annulus). There is a naturally defined continuous function from configuration space $(\theta_A, ...
0
votes
1answer
28 views
+50

Continuity and Differentiation example

I have proved that $g$ is continuous on $(0,2)$ and I just wish to check if my solution for $g$ being right continuous at $0$ and hence continuous at $0$ is correct. $\lim\limits_{x \to 0+}g(x) ...
0
votes
1answer
24 views
+50

Understanding relation between vector valued function and function objective in an multi objective optimization problem

I try to understand the relation between "vector-valued function" and "function objective" as used in optimization problem. I understand that objective function in a multi-objective problem can be ...
4
votes
1answer
74 views
+50

Hessian of a function on Riemannian manifolds

Let $(M,g,\nabla)$ be a Riemannian manifold with metric $g$ and Riemannian connection $\nabla$. The hessian of a function $f:M\to R$ is defined by: $$H^f(X,Y)=g(\nabla_X\ \ \operatorname{grad} ...
6
votes
1answer
137 views
+50

An alternating series identity with a hidden hyperbolic tangent

How does one use the inverse Mellin transform to prove that the following identity holds? $$\sum_{n=1}^{\infty}\frac{(-1)^n}{n(e^{n\pi} + 1)} = \frac{1}{8}(\pi - 5\log(2))$$ The identity follows ...
3
votes
1answer
49 views
+100

Moving the integral $Q(x) = -\frac{e^{-1/2x}}{4i}\int_{1/2-i\infty}^{1/2+i\infty} \zeta(s)\Gamma(\frac{s}{2})\pi^{-s/2}e^{xs} ds$ past Re(s) = 1.

Given the integral $$Q(x) = -\frac{e^{-1/2x}}{4i}\int_{1/2-i\infty}^{1/2+i\infty} \zeta(s)\Gamma(\frac{s}{2})\pi^{-s/2}e^{xs} ds,$$ I know that the integrand is holomorphic except for simple poles at ...
1
vote
1answer
54 views
+250

Gluing submanifolds along their common boundary

Let $M$ be a smooth $m$-manifold and $N_1$, $N_2$ smooth embedded $k$-submanifolds such that $N_1\cap N_2=\partial N_1=\partial N_2$, for each $x\in N_1\cap N_2$, $T_x N_1=T_x N_2$, and for $x\in ...
3
votes
2answers
50 views
+50

Let $H$ be a subgroup of the group $(R, +)$ such that $H$ $∩$ [-1,1] is a finite set containing a non zero element. Show that $H$ is cyclic.

Observations: Since $H$ is a subgroup of $(R, +)$ so $0 \in H.$ If $1 \in H,$ then all positive integers belong to $H.$ But $H$ is closed wrt addition, so the negative integers must belong to $H$ ...
6
votes
0answers
96 views
+50

A set of integers whose elements all divide $2015^{200}$ but do not divide each other

Let $S$ be a set of natural numbers,such that each element divides $2015^{200}$ but for no two elements $a$ and $b$, $a|b$. Find the maximum number of elements in $S$ . $2015^{200}=(5\cdot ...
0
votes
1answer
42 views
+50

Merge two sets, list and tree

We are given two sets $S_1$ and $S_2$. We consider that $S_1$ is implemented, using a sorted list, and $S_2$ is implemented, using a pre-order sorted tree. I have to write a pseudocode, that ...
3
votes
1answer
39 views
+50

Does separation of variables in PDEs give a general solution?

When a partial differential equation is solved using the separation of variables method, is the produced solution the most general one that satisfies the equation or have we lost some forms of the ...