All Questions
5,076 questions with no upvoted or accepted answers
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It is possible to limit a set of curves in the sense $f(x,y) \leq C f(x_0,y)$?
Suppose you have a continuous function $f:[a,b]\times (-\infty, \infty) \rightarrow \mathbb{R}$. I'm trying to understand if it's possible to conclude that due to the compactness of the interval $[a,b]...
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Conjecture that there are finitely many integer powers $a^x$ and $b^y$ such that $b^y - a^x = n$: who first came up with it?
I came up with an interesting mathematical conjecture: for every natural number $n$ there is only a finite number of integer powers $a^x$ and $b^y$ such that $b^y - a^x = n$.
I would like to find out ...
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Modeling player interactions in multi-dimensional rating systems
In traditional rating systems (such as Elo), a player's strength is represented by a single scalar value, which is assumed to be consistent across different opponents. However, in some games, the ...
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What should we call the area for which the lower border is a Motzkin path?
We can draw a Motzkin path from $(0,0)$ to $(n/2,n/2)$ using steps $(0,1)$, $(1,0)$ and $(1/2,1/2)$, such that the path never goes below the line $y=x$. Consider the area bounded by the Motzkin path, ...
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Reference request for the smallest set( resp. abelian group) that a group ( resp. ring ) has a faithful action on
For a proof of the Cayley's Theorem, it is obvious to see that a group ( resp. ring ) has a faithful action on itself by left-multiplication. I would like to extend the result for a bit and find the ...
- 101
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Two particular combinations of Gauss hypergeometric functions
Browsing this site and the web I could not find a reference on the following combinations of Gauss hypergeometric functions $F={}_2F_1$, for which I have reason to believe that they can be simplified ...
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Markov process with time varying transition kernels
I cross post this question from StackExchange as it may be more appropriate.
I am interested in studying the evolution of a variable $\alpha_t\in [0,1]$ governed by the following stochastic dynamical ...
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coupling method for first hitting times
Consider a Markov process $(X_t: S \to S)_{t \ge 0}$ that begins with two initial probabilities $\mu_1$ and $\mu_2$ defined on the state space $S$. Let's define the first hitting time $\tau$ as $\tau:=...
user513728
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On diagonalizations over complexity classes
I am looking for the following PhD thesis, but could not find it, and all my attempts for finding it failed.
I am wondering if there is a way to get it:
On diagonalizations over complexity classes
By: ...
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References on estimates for suprema of uncentered Gaussian processes?
Let $X_t, t \in T$ denote a centered Gaussian process. Let $d(t, s) = \sqrt{\mathbb{E} (X_t - X_s)^2}$.
Consider a mean function $t \mapsto \mu_t$.
Define the expected supremum
$$
S(T, \mu) = \mathbb{...
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Classifier-specific lower bounds on the misclassification rate in binary classification
Consider a binary classification problem for $(X,Y)$, and let $\hat{f}$ be a proposed classifier. We wish to bound the misclassification rate $P(\hat{f}(X)\ne Y)$. There are many known lower bounds on ...
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Additivity of purity of random matrix products
Suppose $M$ is an $n\times n$ matrix with IID random entries drawn from $\mathcal{D}$ and $\sigma$ is the vector of its singular values. Define purity of $M$ as
$$\rho(M)=\frac{n \sum_i \sigma_i^4}{\...
- 2,252
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Gaussian white noise model in application
I am interested in applications (to data) of non-parametric statistics, and my question concerned the Gaussian white noise model defined by,
$$
X_{t_1, \ldots, t_d}=f\left(t_1, \ldots, t_d\right) d ...
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Are there any books or literature on norms over measure space?
Consider the space of signed measures over some abstract space, we know the total variation norm makes the space Banach (I guess). So are some other norms. Are there some books or literature studying ...
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General reference for finite dimensional $*$-algebras over $\mathbb R$?
What references are there for studying finite-dimensional $*$-algebras over the field $\mathbb R$ in their full generality? We assume these are associative and unital.
Note that:
Not every algebra ...
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Real world application of large sets like syndetic sets, central sets
Large sets in $\mathbb{N}$ have strong combinatorial structures. For example, it is known that central sets in $\mathbb{N}$ contain arbitrarily long arithmetic progressions. It also contains solutions ...
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63
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A construction that sort of merges two semigroups to build a new one
Suppose $H$ and $K$ are semigroups and assume without loss of generality that (the underlying sets of) $H$ and $K$ are disjoint. We can then extend the operations of both $H$ and $K$ to a binary ...
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Examples of non $w^{*}$-closed complemented subspaces of a dual Banach space that are also dual spaces
Let $Y$ be a complemented, but not $w^{*}$-closed, subspace of a Banach space $X$. It is known that certain such $Y$ are not dual spaces.
Question: What are interesting examples of subspaces of the ...
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Applications of Jack polynomials
I developed four libraries (Julia, R, Python, Haskell) for the computation of Jack polynomials. I developed them for fun because I found this was programmatically interesting. But now I'd like them to ...
- 2,560
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121
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Quadratic residue problem involving prime divisors of a polynomial
Let $n$ be a square-free natural number, and let $f\in\mathbb{Z}[x]$ be monic and irreducible of degree $\geq2$. I am trying to determine whether there always exists a prime $p$, $p\nmid n$, ...
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Merging two composable walks in a graph
Let $G$ be a graph (i.e., an undirected graph in which we allow for loops and parallel edges). Denote by $V$ the vertex set, by $E$ the edge set, and by $\psi$ the incidence function of $G$, and let $\...
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Sufficient conditions to order the solutions to a system of linear equations
A pretty elementary question, but does anyone know of sufficient conditions to order the solutions of a system of linear equations? For example, in the system, \begin{align*}\begin{bmatrix}a_{11}&...
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Bounds for smallest non-trivial designs
Given $s>t\ge 2$, let $N(s,t)$ be the smallest integer $n>s$ such that there exists an “$(n;s;t;1)$-design” (i.e., a collection of $s$-subsets $e_1,\dots,e_m$ of $[n]:=\{1,\dots,n\}$, such that ...
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145
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Bound on solutions of $Ax \ge b$
Let $A \in \mathbb{Z}^{m \times n}, b \in \mathbb{Z}^{m \times 1}$.
One can show that if there is a solution of $Ax \ge b, x \in \mathbb{R}^n$ then there is one such that $\|x\|_{\infty} \le c (\|A\|_{...
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108
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The study of directional derivatives for functions that are minimums of convex functions
Has research been conducted on the topic of directional derivatives of functions that are minimums of convex functions? It would be greatly appreciated if you could provide the appropriate reference.
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Comparing spectral radius of two graphs using the entry of Perron vector
Suppose we have a graph $G$.
Let $A$ be the adjacency matrix of $G$ and $x$ be the corresponding Perron vector.
Let $x = (x_1,x_2,\cdots,x_n)^t$, where $x_i$ corresponds to the vertex $i \in V(G)$.
We ...
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For curves $C$ of genus $1$, the period (or index?) of $C$ is greater than $1$ iff $C(k)$ is empty
As the title suggests, does anyone have a reference for the proof of this fact? Actually, I can't remember where I've seen it before, or if I even remembered the statement correctly. Here are some ...
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Growing gliders under rule 110
I found a glider in the evolution space of rule 110 that grows constantly in size. Normal gliders live in the so-called ether, e.g. the so-called E-glider:
Other – often complex – gliders exist in an ...
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Extension of primitive set of vectors and reduction theory
Let $\Lambda$ be a unimodular lattice in $\mathbb R^d$ (unimodularity is not really necessary here but just for convenience) and let $B$ be a ball centered at the origin that contains $(k+1)$-many $\...
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Topology of independence set of a vector space
This seems like something that would have a well-known treatment somewhere, but I'm not sure where to look. If we have a vector space $V$ (or maybe even a module), we can consider an abstract ...
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Sum of products on a directed acyclic graph
Is there a textbook/paper that I can reference for the following problem? I am looking for a concise proof that I can cite.
Let $G=(V,E)$ be a weighted directed acyclic graph, and consider
$s,t\in V$....
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On the upper bound estimation of $D(N)$ in Chen Jingrun's theorem
What are the current research results on the estimation of the upper bound of $D(N)$ in Chen Jingrun's theorem?
Including but not limited to Chen Jingrun's improvement 7.8342 and Wu Jie's improvement ...
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86
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Reference request for Poincare-Hopf theorem in a compact submanifold
I recently read the following question about the Poincare-Hopf theorem in a compact submanifold. All the answers were very satisfactory to me. Is there any reference where I can look for more details ...
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141
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Décalage and the simplicial path object
$\DeclareMathOperator\Hom{Hom}\DeclareMathOperator\const{const}$Let $[+1]:\Delta\to\Delta$ be the décalage endomorphism sending $n\mapsto n+1$
adding a new minimal element, i.e. $f:n\to m$ is sent to $...
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Likelihood ratio of non-trivial cycles in an inhomogeneous random square lattice graph embedded on a toroidal surface
Consider a square lattice (random) graph $G$ embedded on a toroidal surface. Each edge $(i, j)$ of the graph has an associated likelihood probability $p_{ij}$. The probabilities $p_{ij}$ come from a ...
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Literature request: proving or disproving convexity of the optimal value function of semidefinite program (SDP) or convex optimization in general
Suppose I have a function $f:\mathbb{R}\rightarrow \mathbb{R}$ defined as the following parametric optimization problem:
$$f(p) = \inf_xf_0(x) \quad \text{subject to } \quad G(x,p)\leq 0,$$
where ...
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Sheaves of abelian groups over a smooth projective variety
Can someone point some good reference (books or lecture notes) for these topics:
Let $X$ a smooth projective variety over an algebraically closed field
Sheaves of abelian groups over $X$
Quasi-...
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Prove that Takens' embedding is a smooth one-to-one map with a smooth inverse
Let $f: \mathcal{M} \rightarrow \mathcal{M}$ be a smooth diffeomorphism and $\phi: \mathcal{M} \rightarrow \mathbb{R}$ be a smooth function, where $\mathcal{M}$ is a $d$-dimensional manifold (which we ...
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Sets measurable in every affine subspace
Take a non-measurable subset $S\subseteq [-1,1]$ and subtract $S\times \{0\}$ from the unit disk $B$ in $\mathbb{R}^2$. The set $X=B\setminus (S\times \{0\})$ is measurable by 2-D Lebesgue measure ...
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Taming families of rate functions
$\newcommand\R{\mathbb R}$Let us say that a function $r\colon\R_+\to\R_+$ is a rate function if $r$ is nondecreasing and $r(x)\to\infty$ as $x\to\infty$.
Let us say that a family $(r_j)_{j\in J}$ of ...
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Reference request: subspace-based generalisation of weak* convergence
Let $V$ be a normed space and $(V_j)_{j\in [0,1]}$ be a family of linear subspaces of $V$ with $V_1$ non-trivial and such that $V_1\subsetneq V_j\subseteq V_i$ whenever $i\leq j$. We write $W:=V'$ for ...
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Counting points on Elliptic Curves with CM by $\mathbb{Q}[\sqrt{-d}]$, $d=1,3$ (CM ring with non-trivial units)
Consider an elliptic curve $E/H$ with CM by the entire ring of integers $\mathcal{O}_K$ of $K=\mathbb{Q}[\sqrt{-d}]$ (and such that $j(E)=j(\mathcal{O}_K)$) such that $H$ is the Hilbert class field of ...
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Reference request: Integrability condition on measures
Let $(\mathcal{C}, \|\cdot\|)$ be a (non-locally compact) Banach space with Borel $\sigma$-algebra $\mathcal{B}$.
Given a probability measure $\mu : \mathcal{B}\rightarrow[0,1]$, I'm interested in ...
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Simultaneous Independent or semi-independent solutions to problems
This is a request for help (with examples, as described below) with a talk I giving to graduate students regarding the dynamics of mathematical research among mathematicians and the development of key ...
- 1,453
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211
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reference for homology complex projective space
I am looking for references on homology complex projective spaces; or more precisely the classification (if any) of smooth oriented manifolds which have the same homology groups as $\mathbb{CP}^n$.
anon
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59
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Identification of vector valued function
Do you know of a good reference for a proof of the fact that $L^2(0,T,L^2(\Omega))$ and to $L^2([0,T]\times \Omega)$ can be identified?
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195
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Definition of union of simplicial complex and a subset
(Cross-posted from MSE: https://math.stackexchange.com/questions/4425225/definition-of-union-of-simplicial-complex-and-a-subset)
Consider a simplicial complex $\Delta$ with vertex set equal to some ...
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196
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Sum of squares squared in an arithmetic progression
Let $r(n)$ be the number of ways to write $n$ as a sum of two squares and $(a,q)=1$.
What is known about
$$
\sum_{n \le x,n \equiv a (\text{mod} \, q)} r(n)^2 \quad?
$$
I am looking for uniform ...
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120
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Does an extension of the B.E.S.T. theorem for multiple Eulerian circuits exist?
Given a directed multigraph $G=(V,E)$ (multiple edges and loops are permitted) the number of distinct Eulerian circuits for $G$ can be calculated with the B.E.S.T. theorem. Does a similar theory for ...
- 1,295
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162
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Compact embedding of anisotropic Sobolev space
I am wondering if the embedding from $W^{2,1}_p(\Omega \times [0,T])$ to $C^{\alpha,\alpha/2}(\Omega \times [0,T])$ is compact, for some suitable domain, $p$ and $\alpha$. I have found some results. I ...
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