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The Chinese restaurant process (CRP) and the stickbreaking process are the two most commonly used representations of the Dirichlet process. However, the usual proof of the connection between them is indirect, relying on abstract properties of the Dirichlet process that are difficult for nonexperts to verify. This short note provides a direct proof that the stickbreaking process leads to the CRP, without using any measure theory. We also discuss how the stickbreaking representation arises naturally from the CRP.
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The M\"obius invariant space $\mathcal{Q}_p$, $0<p<\infty$, consists of functions $f$ which are analytic in the open unit disk $\mathbb{D}$ with $$ \f\_{\mathcal{Q}_p}=f(0)+\sup_{w\in \D} \left(\int_\D f'(z)^2(1\sigma_w(z)^2)^p dA(z)\right)^{1/2}<\infty, $$ where $\sigma_w(z)=(wz)/(1\overline{w}z)$ and $dA$ is the area measure on $\mathbb{D}$. It is known that the following inequality $$ f(0)+\sup_{w\in \D} \left(\int_\D \left\frac{f(z)f(w)}{1\overline{w}z}\right^2 (1\sigma_w(z)^2)^p dA(z)\right)^{1/2} \lesssim \f\_{\mathcal{Q}_p} $$ played a key role to characterize multipliers and certain Carleson measures for $\mathcal{Q}_p$ spaces. The converse of the inequality above is a conjecturedinequality in [14]. In this paper, we show that this conjecturedinequality is true for $p>1$ and it does not hold for $0<p\leq 1$.
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We show that the threedimensional homology cobordism group admits an infiniterank summand. It was previously known that the homology cobordism group contains a $\mathbb{Z}^\infty$subgroup and a $\mathbb{Z}$summand. Our proof proceeds by introducing an algebraic variant of the involutive Heegaard Floer package of HendricksManolescu and HendricksManolescuZemke. This is inspired by an analogous argument in the setting of knot concordance due to the second author.
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In the Ising model, we consider the problem of estimating the covariance of the spins at two specified vertices. In the ferromagnetic case, it is easy to obtain an additive approximation to this covariance by repeatedly sampling from the relevant Gibbs distribution. However, we desire a multiplicative approximation, and it is not clear how to achieve this by sampling, given that the covariance can be exponentially small. Our main contribution is a fully polynomial time randomised approximation scheme (FPRAS) for the covariance. We also show that that the restriction to the ferromagnetic case is essential  there is no FPRAS for multiplicatively estimating the covariance of an antiferromagnetic Ising model unless RP = #P. In fact, we show that even determining the sign of the covariance is #Phard in the antiferromagnetic case.
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We develop a phasefield approximation of the relaxation of the perimeter functional in the plane under a connectedness constraint based on the classical ModicaMortola functional and the connectedness constraint of (Dondl, Lemenant, Wojtowytsch 2017). We prove convergence of the approximating energies and present numerical results and applications to image segmentation.
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For a separable finite diffuse measure space $\mathcal{M}$ and an orthonormal basis $\{\varphi_n\}$ of $L^2(\mathcal{M})$ consisting of bounded functions $\varphi_n\in L^\infty(\mathcal{M})$, we find a measurable subset $E\subset\mathcal{M}$ of arbitrarily small complement $\mathcal{M}\setminus E<\epsilon$, such that every measurable function $f\in L^1(\mathcal{M})$ has an approximant $g\in L^1(\mathcal{M})$ with $g=f$ on $E$ and the Fourier series of $g$ converges to $g$, and a few further properties. The subset $E$ is universal in the sense that it does not depend on the function $f$ to be approximated. Further in the paper this result is adapted to the case of $\mathcal{M}=G/H$ being a homogeneous space of an infinite compact second countable Hausdorff group. As a useful illustration the case of $n$spheres with spherical harmonics is discussed. The construction of the subset $E$ and approximant $g$ is sketched briefly at the end of the paper.
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Consider a dynamic random geometric social network identified by $s_t$ independent points $x_t^1,\ldots,x_t^{s_t}$ in the unit square $[0,1]^2$ that interact in continuous time $t\geq 0$. The generative model of the random points is a Poisson point measures. Each point $x_t^i$ can be active or not in the network with a Bernoulli probability $p$. Each pair being connected by affinity thanks to a step connection function if the interpoint distance $\x_t^ix_t^j\\leq a_\mathsf{f}^\star$ for any $i\neq j$. We prove that when $a_\mathsf{f}^\star=\sqrt{\frac{(s_t)^{l1}}{p\pi}}$ for $l\in(0,1)$, the number of isolated points is governed by a Poisson approximation as $s_t\to\infty$. This offers a natural threshold for the construction of a $a_\mathsf{f}^\star$neighborhood procedure tailored to the dynamic clustering of the network adaptively from the data.
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In this paper, we study the atomic structure of certain classes of semigroup algebras whose sets of exponents are additive submonoids of rational numbers. When studying the atomicity of integral domains, the building blocks by excellence are the irreducible elements. Here we start by extending the Gauss's Lemma and the Eisenstein's Criterion from polynomial rings to semigroup rings with rational exponents. Then we prove that semigroup algebras whose exponent sets are submonoids of $\langle 1/p \mid p \ \text{ is prime} \rangle$ are atomic. Next, for every algebraic closed field $F$, we exhibit a class of Bezout semigroup algebras over $F$ with rational exponents whose members are antimatter, i.e., contain no atoms. In addition, we use a class of rootclosed additive submonoids of rationals to construct another class of antimatter semigroup algebras over any perfect field of finite characteristic. Finally, we characterize the irreducible elements of semigroup algebras whose exponent sem
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It is becoming increasingly common to see large collections of network data objects  that is, data sets in which a network is viewed as a fundamental unit of observation. As a result, there is a pressing need to develop networkbased analogues of even many of the most basic tools already standard for scalar and vector data. In this paper, our focus is on averages of unlabeled, undirected networks with edge weights. Specifically, we (i) characterize a certain notion of the space of all such networks, (ii) describe key topological and geometric properties of this space relevant to doing probability and statistics thereupon, and (iii) use these properties to establish the asymptotic behavior of a generalized notion of an empirical mean under sampling from a distribution supported on this space. Our results rely on a combination of tools from geometry, probability theory, and statistical shape analysis. In particular, the lack of vertex labeling necessitates working with a quotient space
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Quadratic backward stochastic differential equations with singularity in the value process appear in several applications, including stochastic control and physics. In this paper, we prove existence and uniqueness of equations with generators (dominated by a function) of the form $z^2/y$. In the particular case where the BSDE is Markovian, we obtain existence of viscosity solutions of singular quadratic PDEs with and without Neumann lateral boundaries, and rather weak assumptions on the regularity of the coefficients. Furthermore, we show how our results can be applied to optimization problems in finance.
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Highspeed trains (HSTs) are being widely deployed around the world. To meet the highrate data transmission requirements on HSTs, millimeter wave (mmWave) HST communications have drawn increasingly attentions. To realize sufficient link margin, mmWave HST systems employ directional beamforming with large antenna arrays, which results in that the channel estimation is rather timeconsuming. In HST scenarios, channel conditions vary quickly and channel estimations should be performed frequently. Since the period of each transmission time interval (TTI) is too short to allocate enough time for accurate channel estimation, the key challenge is how to design an efficient beam searching scheme to leave more time for data transmission. Motivated by the successful applications of machine learning, this paper tries to exploit the similarities between current and historical wireless propagation environments. Using the knowledge of reinforcement learning, the beam searching problem of mmWave HST
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We find a decomposition formula of the local BayerMacr\`i map for the nef line bundle theory on the Bridgeland moduli space over surface. If there is a global BayerMacr\`i map, such decomposition gives a precise correspondence from Bridgeland walls to Mori walls. As an application, we compute the nef cone of the Hilbert scheme $S^{[n]}$ of $n$points over special kinds of fibered surface $S$ of Picard rank two.
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We study biLagrangian structures (a symplectic form with a pair of complementary Lagrangian foliations, also known as paraK\"ahler or K\"unneth structures) on nilmanifolds of dimension less than or equal to 6. In particular, building on previous work of several authors, we determine which 6dimensional nilpotent Lie algebras admit a biLagrangian structure. In dimension 6, there are (up to isomorphism) 26 nilpotent Lie algebras which admit a symplectic form, 16 of which admit a biLagrangian structure and 10 of which do not. We also calculate the curvature of the canonical connection of these biLagrangian structures.
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A new version of the change of the "phase" (i.e., of the set of observable characteristics) of a quantum system is proposed. In a general scenario the evolution is assumed generated, before the phase transition, by some standard Hermitian Hamiltonian $H^{(before)}$, and, after the phase transition, by one of the recently very popular nonstandard, nonHermitian (but hiddenly Hermitian, i.e., still unitarityguaranteeing) Hamiltonians $H^{(after)}$. For consistency, a smoothness of matching between the two operators as well as between the related physical Hilbert spaces must be guaranteed. The feasibility of the idea is illustrated via the twomode $(N1)$bosonic BoseHubbard Hamiltonian. In $H^{(before)}=H^{(BH)}(\varepsilon)$ we use the decreasing real $\varepsilon^{(before)} \to 0$. In the hiddenly Hermitian continuation $H^{(after)}=H^{(BH)}(\tilde{\varepsilon})$ the imaginary part of the purely imaginary $\tilde{\varepsilon}^{(after)}$ grows. The smoothness of the transition occur
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We study the effect of small random advection in two models in turbulent combustion. Assuming that the velocity field decorrelates sufficiently fast, we (i) identify the order of the fluctuations of the front with respect to the size of the advection, and (ii) characterize them by the solution of a HamiltonJacobi equation forced by white noise. In the simplest case, the result yields, for both models, a front with Brownian fluctuations of the same scale as the size of the advection. That the fluctuations are the same for both models is somewhat surprising, in view of known differences between the two models.
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We study the problem of caching optimization in heterogeneous networks with mutual interference and perfile rate constraints from an energy efficiency perspective. A setup is considered in which two cacheenabled transmitter nodes and a coordinator node serve two users. We analyse and compare two approaches: (i) a cooperative approach where each of the transmitters might serve either of the users and (ii) a noncooperative approach in which each transmitter serves only the respective user. We formulate the cache allocation optimization problem so that the overall system power consumption is minimized while the use of the link from the master node to the end users is spared whenever possible. We also propose a lowcomplexity optimization algorithm and show that it outperforms the considered benchmark strategies. Our results indicate that significant gains both in terms of power saving and sparing of master node's resources can be obtained when full cooperation between the transmitters
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We propose a purely probabilistic model to explain the evolution path of a population maximum fitness. We show that after $n$ births in the population there are about $\ln n$ upwards jumps. This is true for any mutation probability and any fitness distribution and therefore suggests a general law for the number of upwards jumps. Simulations of our model show that a typical evolution path has first a steep rise followed by long plateaux. Moreover, independent runs show parallel paths. This is consistent with what was observed by Lenski and Travisano (1994) in their bacteria experiments.
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We study the problem of finding good gauges for connections in higher gauge theories. We find that, for $2$connections in strict $2$gauge theory and $3$connections in $3$gauge theory, there are local "Coulomb gauges" that are more canonical than in classical gauge theory. In particular, they are essentially unique, and no smallness of curvature is needed in the critical dimensions. We give natural definitions of $2$YangMills and $3$YangMills theory and find that the choice of good gauges makes them essentially linear. As an application, (anti)selfdual $2$connections over $B^6$ are always $2$YangMills, and (anti)selfdual $3$connections over $B^8$ are always $3$YangMills.
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Recently, in their pioneering work on the subject of biunivalent functions, Srivastava et al. \cite{HMSAKMPG} actually revived the study of the coefficient problems involving biunivalent functions. Inspired by the pioneering work of Srivastava et al. \cite{HMSAKMPG}, there has been triggering interest to study the coefficient problems for the different subclasses of biunivalent functions. Motivated largely by Ali et al. \cite{AliRaviMaMinaclass}, Srivastava et al. \cite{HMSAKMPG} and G\"{u}ney et al. \cite{HOGGMSJSFib2018} in this paper, we consider certain classes of biunivalent functions related to shelllike curves connected with Fibonacci numbers to obtain the estimates of second, third TaylorMaclaurin coefficients and Fekete  Szeg\"{o} inequalities. Further, certain special cases are also indicated. Some interesting remarks of the results presented here are also discussed.
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We study spherical completeness of ball spaces and its stability under expansions. We introduce the notion of an ultradiameter, mimicking diameters in ultrametric spaces. We prove some positive results on preservation of spherical completeness involving ultradiameters with values in narrow partially ordered sets. Finally, we show that in general, chain intersection closures of ultrametric spaces with partially ordered value sets do not preserve spherical completeness.
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We show that any neighborhood of a nondegenerate reversible bifocal homoclinic orbit contains chaotic suspended invariant sets on $N$symbols for all $N\geq 2$. This will be achieved by showing switching associated with networks of secondary homoclinic orbits. We also prove the existence of superhomoclinic orbits (trajectories homoclinic to a network of homoclinic orbits), whose presence leads to a particularly rich structure.
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We provide a detailed analysis of the boundary layers for mixed hyperbolicparabolic systems in one space dimension and small amplitude regimes. As an application of our results, we describe the solution of the socalled boundary Riemann problem recovered as the zero viscosity limit of the physical viscous approximation. In particular, we tackle the so called doubly characteristic case, which is considerably more demanding from the technical viewpoint and occurs when the boundary is characteristic for both the mixed hyperbolicparabolic system and for the hyperbolic system obtained by neglecting the second order terms. Our analysis applies in particular to the compressible NavierStokes and MHD equations in Eulerian coordinates, with both positive and null conductivity. In these cases, the doubly characteristic case occurs when the velocity is close to 0. The analysis extends to nonconservative systems.
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By extrapolating the explicit formula of the zerobias distribution occurring in the context of Stein's method, we construct characterization identities for a large class of absolutely continuous univariate distributions. Instead of trying to derive characterizing distributional transformations that inherit certain structures for the use in further theoretic endeavours, we focus on explicit representations given through a formula for the distribution function. The results we establish with this ambition feature immediate applications in the area of goodnessoffit testing. We draw up a blueprint for the construction of tests of fit that include procedures for many distributions for which little (if any) practicable tests are known.
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An old open problem in number theory is whether Chebotarev density theorem holds in short intervals. More precisely, given a Galois extension $E$ of $\mathbb{Q}$ with Galois group $G$, a conjugacy class $C$ in $G$ and an $1\geq \varepsilon>0$, one wants to compute the asymptotic of the number of primes $x\leq p\leq x+x^{\varepsilon}$ with Frobenius conjugacy class in $E$ equal to $C$. The level of difficulty grows as $\varepsilon$ becomes smaller. Assuming the Generalized Riemann Hypothesis, one can merely reach the regime $1\geq\varepsilon>1/2$. We establish a function field analogue of Chebotarev theorem in short intervals for any $\varepsilon>0$. Our result is valid in the limit when the size of the finite field tends to $\infty$ and when the extension is tamely ramified at infinity. The methods are based on a higher dimensional explicit Chebotarev theorem, and applied in a much more general setting of arithmetic functions, which we name $G$factorization arithmetic functio
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A fullness conjecture of Kuznetsov says that if a smooth projective variety $X$ admits a full exceptional collection of line bundles of length $l$, then any exceptional collection of line bundles of length $l$ is full. In this paper, we show that this conjecture holds for $X$ as the blowup of $\mathbb{P}^{3}$ at a point, a line, or a twisted cubic curve, i.e. any exceptional collection of line bundles of length 6 on $X$ is full. Moreover, we obtain an explicit classification of full exceptional collections of line bundles on such $X$.
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We classify all edgetoedge spherical isohedral 4gonal tilings such that the skeletons are pseudodouble wheels. For this, we characterize these spherical tilings by a quadratic equation for the cosine of an edgelength. By the classification, we see: there are indeed two noncongruent, edgetoedge spherical isohedral 4gonal tilings such that the skeletons are the same pseudodouble wheel and the cyclic list of the four inner angles of the tiles are the same. This contrasts with that every edgetoedge spherical tiling by congruent 3gons is determined by the skeleton and the inner angles of the skeleton. We show that for a particular spherical isohedral tiling over the pseudodouble wheel of twelve faces, the quadratic equation has a double solution and the copies of the tile also organize a spherical nonisohedral tiling over the same skeleton.
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The goal of this paper is to classify fusion categories $\otimes$generated by a $K$normal object (defined in this paper) of FrobeniusPerron dimension less than 2. This classification has recently become accessible due to a result of Morrison and Snyder, showing that any such category must be a cyclic extension of a category of adjoint $ADE$ type. Our main tools in this classification are the results of Etingof, Ostrik, and Nikshych, classifying cyclic extensions of a given category in terms of data computed from the BrauerPicard group, and Drinfeld centre of that category, and the results of the author, which compute the BrauerPicard group and Drinfeld centres of the categories of adjoint $ADE$ type. Our classification includes the expected categories, constructed from cyclic groups and the categories of $ADE$ type. More interestingly we have categories in our classification that are nontrivial deequivariantizations of these expected categories. Most interesting of all, our clas
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In this paper we use a gradient flow to deform closed planar curves to curves with least variation of geodesic curvature in the $L^2$ sense. Given a smooth initial curve we show that the solution to the flow exists for all time and, provided the length of the evolving curve remains bounded, smoothly converges to a multiplycovered circle. Moreover, we show that curves in any homotopy class with initially small $L^3\lVert k_s\rVert_2^2$ enjoy a uniform length bound under the flow, yielding the convergence result in these cases.
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For a graph $G$, let $\chi(G)$ and $\omega(G)$ respectively denote the chromatic number and clique number of $G$. We give an explicit structural description of ($P_5$,gem)free graphs, and show that every such graph $G$ satisfies $\chi(G)\le \lceil\frac{5\omega(G)}{4}\rceil$. Moreover, this bound is best possible.
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We study compact operators on the Bergman space of the Thullen domain defined by $\{(z_1,z_2)\in \mathbb C^2: z_1^{2p}+z_2^2<1\}$ with $p>0$ and $p\neq 1$. The domain need not be smooth nor have a transitive automorphism group. We give a sufficient condition for the boundedness of various operators on the Bergman space. Under this boundedness condition, we characterize the compactness of operators on the Bergman space of the Thullen domain.
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We introduce the notion of complex $G_2$ manifold $M_{\mathbb C}$, and complexification of a $G_2$ manifold $M\subset M_{\mathbb C}$. As an application we show the following: If $(Y,s)$ is a closed oriented $3$manifold with a $Spin^{c}$ structure, and $(Y,s)\subset (M, \varphi)$ is an imbedding as an associative submanifold of some $G_2$ manifold (such imbedding always exists), then the isotropic associative deformations of $Y$ in the complexified $G_2$ manifold $M_{\mathbb C}$ is given by SeibergWitten equations.
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We consider the algorithmic problem of computing the partition function of the SherringtonKirkpatrick model of spin glasses with Gaussian couplings. We show that there is no polynomial time algorithm for computing the partition function exactly (in the sense to be made precise), unless P=\#P. Our proof uses the Lipton's reducibility trick of computation modulo large primes~\cite{lipton1991new} and nearuniformity of the lognormal distribution in small intervals. To the best of our knowledge, this is the first statistical physics model with random parameters for which such average case hardness is established.
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The principal angles between binary collision subspaces in an $N$billiard system in $m$dimensional Euclidean space are computed. These angles are computed for equal masses and arbitrary masses. We then provide a bound on the number of collisions in the planar 3billiard system problem. Comparison of this result with known billiard collision bounds in lower dimensions is discussed.
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We are studying possible interaction of damping coefficients in the subprincipal part of the linear 3D wave equation and their impact on the critical exponent of the corresponding nonlinear Cauchy problem with small initial data. The main new phenomena is that certain relation between these coefficients may cause very strong jump of the critical Strauss exponent in 3D to the critical 5D Strauss exponent for the wave equation without damping coefficients.
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Identifying the unknown underlying trend of a given noisy signal is extremely useful for a wide range of applications. The number of potential trends might be exponential, which can be computationally exhaustive even for short signals. Another challenge, is the presence of abrupt changes and outliers at unknown times which impart resourceful information regarding the signal's characteristics. In this paper, we present the $\ell_1$ Adaptive Trend Filter, which can consistently identify the components in the underlying trend and multiple levelshifts, even in the presence of outliers. Additionally, an enhanced coordinate descent algorithm which exploit the filter design is presented. Some implementation details are discussed and a version in the Julia language is presented along with two distinct applications to illustrate the filter's potential.
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In this short note, we consider order convergence in the space of all Banach lattice valued Bochner integrable functions instead of almost everywhere pointwise convergence to establish two results similar to the monotone convergence theorem and the Fatou's lemma; this approach has two advantages: we can use nets instead of sequences and no monotonicity is required.
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We give two characterizations of tracially nuclear C*algebras. The first is that the finite summand of the second dual is hyperfinite. The second is in terms of a variant of the weak* uniqueness property. The necessary condition holds for all tracially nuclear C*algebras. When the algebra is separable, we prove the sufficiency.
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Let $G$ be a finite group and let $\pi$ be a set of primes. In this paper, we prove a criterion for the existence of a solvable $\pi$Hall subgroup of $G$, precisely, the group $G$ has a solvable $\pi$Hall subgroup if, and only if, $G$ has a $\{p,q\}$Hall subgroup for any pair $p$, $q\in\pi$.
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Consider the classical problem of solving a general linear system of equations $Ax=b$. It is well known that the (successively over relaxed) GaussSeidel scheme and many of its variants may not converge when $A$ is neither diagonally dominant nor symmetric positive definite. Can we have a linearly convergent GS type algorithm that works for any $A$? In this paper we answer this question affirmatively by proposing a doubly stochastic GS algorithm that is provably linearly convergent (in the mean square error sense) for any feasible linear system of equations. The key in the algorithm design is to introduce a nonuniform double stochastic scheme for picking the equation and the variable in each update step as well as a stepsize rule. These techniques also generalize to certain iterative alternating projection algorithms for solving the linear feasibility problem $A x\le b$ with an arbitrary $A$, as well as certain highdimensional convex minimization problems. Our results demonstrate th
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The wireless channel of 5G communications will have unique characteristics that can not be fully apprehended by the traditional fading models. For instance, the wireless channel may often be dominated by a finite number of specular components, the conventional Gaussian assumption may not be applied to the diffuse scattered waves and the point scatterers may be inhomogeneously distributed. These physical attributes were incorporated into the stateoftheart fading models, such as the kappamu shadowed fading model, the generalized tworay fading model, and the fluctuating two ray fading model. Unfortunately, much of the existing published work commonly imposed arbitrary assumptions on the channel parameters to achieve theoretical tractability, thereby limiting their application to represent a diverse range of propagation environments. This motivates us to find a more general fading model that incorporates multiple specular components with clusterized diffuse scattered waves, but achiev
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A family $F$ of graphs on a fixed set of $n$ vertices is called triangleintersecting if for any $G_1,G_2 \in F$, the intersection $G_1 \cap G_2$ contains a triangle. More generally, for a fixed graph $H$, a family $F$ is $H$intersecting if the intersection of any two graphs in $F$ contains a subgraph isomorphic to $H$. In [D. Ellis, Y. Filmus, and E. Friedgut, Triangleintersecting families of graphs, J. Eur. Math. Soc. 14 (2012), pp. 841885], Ellis, Filmus and Friedgut proved a 36year old conjecture of Simonovits and S\'{o}s stating that the maximal size of a triangleintersecting family is $(1/8)2^{n(n1)/2}$. Furthermore, they proved a $p$biased generalization, stating that for any $p \leq 1/2$, we have $\mu_{p}(F)\le p^{3}$, where $\mu_{p}(F)$ is the probability that the random graph $G(n,p)$ belongs to $F$. In the same paper, Ellis et al. conjectured that the assertion of their biased theorem holds also for $1/2 < p \le 3/4$, and more generally, that for any non$t$colo
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We describe a convex relaxation for the GilbertSteiner problem both in $R^d$ and on manifolds, extending the framework proposed in [9], and we discuss its sharpness by means of calibration type arguments. The minimization of the resulting problem is then tackled numerically and we present results for an extensive set of examples. In particular we are able to address the Steiner tree problem on surfaces.
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In this paper, we present a minimal chordal completion $G^*$ of a graph $G$ satisfying the inequality $\omega(G^*)  \omega(G) \le i(G)$ for the nonchordality index $i(G)$ of $G$. In terms of our chordal completions, we partially settle the Hadwiger conjecture and the Erd\H{o}sFaberLov\'{a}sz Conjecture, and extend the known $\chi$bounded class by adding to it the family of graphs with bounded nonchordality indices.
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We consider a onephase free boundary problem of the minimizer of the energy \[ J_{\gamma}(u)=\frac{1}{2}\int_{(B_1^{n+1})^+}{y^{12s}\nabla u(x,y)^2dxdy}+\int_{B_1^{n}\times \{y=0\}}{u^{\gamma}dx}, \] with constants $0<s,\gamma<1$. It is an intermediate case of the fractional cavitation problem (as $\gamma=0$) and the fractional obstacle problem (as $\gamma=1$). We prove that the blowup near every free boundary point is homogeneous of degree $\beta=\frac{2s}{2\gamma}$, and flat free boundary is $C^{1,\theta}$ when $\gamma$ is close to 0.
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In this note we are interested in the dynamics of the linear flow on infinite periodic $\mathbb{Z}^d$covers of Veech surfaces. An elementary remark allows us to show that the kernel of some natural representations of the Veech group acting on homology is "big". In particular, the same is true for the Veech group of the infinite surface, answering a question of Pascal Hubert. We give some applications to the dynamics on windtree models where the underlying compact translation surface is a Veech surface.
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If $K$ is a field of characteristic $p$ then the $p$torsion of the Brauer group, ${}_p{\rm Br\,}(K)$, is represented by a quotient of the group of $1$forms, $\Omega^1(K)$. Namely, we have a group isomorphism $$\alpha_p:\Omega^1(K)/\langle{\rm d}a,\, (a^pa){\rm dlog}b\, :\, a,b\in K,\, b\neq 0\rangle\to{}_p{\rm Br\,}(K),$$ given by $a{\rm d}b\mapsto [ab,b)_p$ $\forall a,b\in K$, $b\neq 0$. Here $[\cdot,\cdot )_p:K/\wp (K)\times K^\times/K^{\times p}\to{}_p{\rm Br\,}(K)$ denotes the ArtinSchreier symbol. In this paper we generalize this result. Namely, we prove that for every $n\geq 1$ we have a representation of ${}_{p^n}{\rm Br\,}(K)$ by a quotient of $\Omega^1(W_n(K))$, where $W_n(K)$ is the truncation of length $n$ of the ring of $p$typical Witt vectors, i.e. $W_{\{1,p,\ldots,p^{n1}\}}(K)$. Explicitly, we have a group isomorphism $$\alpha_{p^n}:\Omega^1(W_{p^n}(K))/\langle Fa{\rm d}ba{\rm d}Vb\, :\, a,b\in W_n(K),\, ([a^p][a]){\rm dlog}[b]\, :\, a,b\in K,\, b\neq 0\rangle\to{
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We construct a tower of fibrations approximating the derived mapping space between two simplicially enriched operads subject to mild conditions. The nth stage of the tower is obtained by neglecting operations with more than n inputs. The main theorem describes the layers of this tower.
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Let $(M,\textit{g},\sigma)$ be a compact Riemannian spin manifold of dimension $m\geq2$, let $\mathbb{S}(M)$ denote the spinor bundle on $M$, and let $D$ be the AtiyahSinger Dirac operator acting on spinors $\psi:M\to\mathbb{S}(M)$. We study the existence of solutions of the nonlinear Dirac equation with critical exponent \[ D\psi = \lambda\psi + f(\psi)\psi + \psi^{\frac2{m1}}\psi \tag{NLD} \] where $\lambda\in\mathbb{R}$ and $f(\psi)\psi$ is a subcritical nonlinearity in the sense that $f(s)=o\big(s^{\frac2{m1}}\big)$ as $s\to\infty$. A model nonlinearity is $f(s)=\alpha s^{p2}$ with $2<p<\frac{2m}{m1}$, $\alpha\in\mathbb{R}$. In particular we study the nonlinear Dirac equation \[ D\psi=\lambda\psi+\psi^{\frac2{m1}}\psi, \quad \lambda\in\mathbb{R}. \tag{BND} \] This equation is a spinorial analogue of the BrezisNirenberg problem. As corollary of our main results we obtain the existence of nontrivial solutions $(\lambda,\psi)$ of (BND) for every $\lambda>0$, ev
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We present an optimal algorithm for the threestage arbitrary polarization tracking using LithiumNiobatebased Polarization Controllers: device calibration, polarization state rotation, and stabilization. The theoretical model representing the lithiumniobatebased polarization controller is derived and the methodology is successfully applied. Results are numerically simulated in the MATLAB environment.
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We develop a model for an antiplane crack defect posed on a square lattice under an interatomic pairpotential with nearestneighbour interactions. In particular, we establish existence, local uniqueness and stability of solutions for small loading parameters and further prove qualitatively sharp farfield decay estimates. The latter requires establishing decay estimates for the corresponding lattice Green's function, which are of independent interest.
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In this paper, we study the asymptotic behavior of BV functions in complete metric measure spaces equipped with a doubling measure supporting a $1$Poincar\'e inequality. We show that at almost every point $x$ outside the Cantor and jump parts of a BV function, the asymptotic limit of the function is a Lipschitz continuous function of least gradient on a tangent space to the metric space based at $x$. We also show that, at codimension $1$ Hausdorff measure almost every measuretheoretic boundary point of a set $E$ of finite perimeter, there is an asymptotic limit set $(E)_\infty$ corresponding to the asymptotic expansion of $E$ and that every such asymptotic limit $(E)_\infty$ is a quasiminimal set of finite perimeter. We also show that the perimeter measure of $(E)_\infty$ is Ahlfors codimension $1$ regular.
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We define automorphic vector bundles on the stack of $G$zips introduced by MoonenPinkWedhornZiegler and study their global sections. In particular, we give a combinatorial condition on the weight for the existence of nonzero mod $p$ automorphic forms on Shimura varieties of Hodgetype. We attach to the highest weight of the representation $V(\lambda)$ a mod $p$ automorphic form and we give a modular interpretation of this form in some cases.
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We classify all possible automorphism groups of smooth cubic surfaces over an algebraically closed field of arbitrary characteristic. As an intermediate step we also classify automorphism groups of quartic del Pezzo surfaces. We show that the moduli space of smooth cubic surfaces is rational in every characteristic, determine the dimensions of the strata admitting each possible isomorphism class of automorphism group, and find explicit normal forms in each case. Finally, we completely characterize when a smooth cubic surface in positive characteristic, together with a group action, can be lifted to characteristic zero.
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Starting from a generalization of the standard axioms for a monoid we present a stepwise development of various, mutually equivalent foundational axiom systems for category theory. Our axiom sets have been formalized in the Isabelle/HOL interactive proof assistant, and this formalization utilizes a semantically correct embedding of free logic in classical higherorder logic. The modeling and formal analysis of our axiom sets has been significantly supported by series of experiments with automated reasoning tools integrated with Isabelle/HOL. We also address the relation of our axiom systems to alternative proposals from the literature, including an axiom set proposed by Freyd and Scedrov for which we reveal a technical issue (when encoded in free logic where free variables range over defined and undefined objects): either all operations, e.g. morphism composition, are total or their axiom system is inconsistent. The repair for this problem is quite straightforward, however.
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We define the mechanical complexity $C(P)$ of a convex polyhedron $P,$ interpreted as a homogeneous solid, as the difference between the total number of its faces, edges and vertices and the number of its static equilibria, and the mechanical complexity $C(S,U)$ of primary equilibrium classes $(S,U)^E$ with $S$ stable and $U$ unstable equilibria as the infimum of the mechanical complexity of all polyhedra in that class. We prove that the mechanical complexity of a class $(S,U)^E$ with $S, U > 1$ is the minimum of $2(f+vSU)$ over all polyhedral pairs $(f,v )$, where a pair of integers is called a polyhedral pair if there is a convex polyhedron with $f$ faces and $v$ vertices. In particular, we prove that the mechanical complexity of a class $(S,U)^E$ is zero if, and only if there exists a convex polyhedron with $S$ faces and $U$ vertices. We also discuss the mechanical complexity of the monostatic classes $(1,U)^E$ and $(S,1)^E$, and offer a complexitydependent prize for the compl
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Let G be a reductive padic group. Let $\Phi$ be an invariant distribution on G lying in the Bernstein center Z(G). We prove that $\Phi$ is supported on compact elements in G if and only if it defines a constant function on every component of the set Irr(G); in particular, we show that the space of all elements of Z(G) supported on compact elements is a subalgebra of Z(G). Our proof is a slight modiification of the arguments of J.F.Dat who proved our result in one direction.
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It is well known that, given a $2d$ purely magnetic Landau Hamiltonian with a constant magnetic field $b$ which generates a magnetic flux $\varphi$ per unit area, then any spectral island $\sigma_b$ consisting of $M$ infinitely degenerate Landau levels carries an integrated density of states $\mathcal{I}_b=M \varphi$. Wannier later discovered a similar Diophantine relation expressing the integrated density of states of a gapped group of bands of the Hofstadter Hamiltonian as a linear function of the magnetic field flux with integer slope. We extend this result to a gap labelling theorem for any $2d$ BlochLandau operator $H_b$ which also has a bounded $\mathbb{Z}^2$periodic electric potential. Assume that $H_b$ has a spectral island $\sigma_b$ which remains isolated from the rest of the spectrum as long as $\varphi$ lies in a compact interval $[\varphi_1,\varphi_2]$. Then $\mathcal{I}_b=c_0+c_1\varphi$ on such intervals, where the constant $c_0\in \mathbb{Q}$ while $c_1\in \mathbb{Z}$
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The heavytailed distributions of corrupted outliers and singular values of all channels in lowlevel vision have proven effective priors for many applications such as background modeling, photometric stereo and image alignment. And they can be well modeled by a hyperLaplacian. However, the use of such distributions generally leads to challenging nonconvex, nonsmooth and nonLipschitz problems, and makes existing algorithms very slow for largescale applications. Together with the analytic solutions to lpnorm minimization with two specific values of p, i.e., p=1/2 and p=2/3, we propose two novel bilinear factor matrix norm minimization models for robust principal component analysis. We first define the double nuclear norm and Frobenius/nuclear hybrid norm penalties, and then prove that they are in essence the Schatten1/2 and 2/3 quasinorms, respectively, which lead to much more tractable and scalable Lipschitz optimization problems. Our experimental analysis shows that both our m
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We use bioriented incidence relations in order to construct a KempfLaksov type resolution for any Schubert variety of the complete flag manifold but also an embedded resolution for any Schubert variety in the Grassmannian. These constructions are alternatives to the celebrated BottSamelson resolutions. The second process led to the introduction of singular flag varieties, algebrogeometric objects that interpolate between the standard flag manifolds and products of Grassmannians, but which are singular in general. The surprising simple desingularization of a particular singular flag variety produces an embedded resolution of the Schubert variety within the Grassmannian.
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On a bounded strictly pseudoconvex domain in $\mathbb{C}^n$, $n>1$, the smoothness of the ChengYau solution to Fefferman's complex MongeAmpere equation up to the boundary is obstructed by a local CR invariant of the boundary. For a bounded strictly pseudoconvex domain $\Omega\subset \mathbb{C}^2$ diffeomorphic to the ball, we prove that the global vanishing of this obstruction implies biholomorphic equivalence to the unit ball, subject to the existence of a holomorphic vector field satisfying a mild approximate tangency condition along the boundary. In particular, by considering the Euler vector field multiplied by $i$ the result applies to all domains in a large $C^1$ open neighborhood of the unit ball in $\mathbb{C}^2$. The proof rests on establishing an integral identity involving the CR curvature of $\partial \Omega$ for any holomorphic vector field defined in a neighborhood of the boundary. The notion of ambient holomorphic vector field along the CR boundary generalizes natur
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The rise of electric vehicles (EVs) is unstoppable due to factors such as the decreasing cost of batteries and various policy decisions. These vehicles need to be charged and will therefore cause congestion in local distribution grids in the future. Motivated by this, we consider a charging station with finitely many parking spaces, in which electric vehicles arrive in order to get charged. An EV has a random parking time and a random charging time. Both the charging rate per vehicle and the charging rate possible for the station are assumed to be limited. Thus, the charging rate of uncharged EVs depends on the number of cars charging simultaneously. This model leads to a layered queueing network in which parking spaces with EV chargers have a dual role, of a server (to cars) and customers (to the grid). We are interested in the performance of the aforementioned model, focusing on the fraction of vehicles that get fully charged. To do so, we develop several bounds and asymptotic (fluid
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We introduce the class of Cartan triples as a generalization of the notion of a Cartan MASA in a von Neumann algebra. We obtain a onetoone correspondence between Cartan triples and certain Clifford extensions of inverse semigroups. Moreover, there is a spectral theorem describing bimodules in terms of their support sets in the fundamental inverse semigroup and, as a corollary, an extension of Aoi's theorem to this setting. This context contains that of Fulman's generalization of Cartan MASAs and we discuss his generalization in an appendix.
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We introduce a categorical analogue of Saito's notion of primitive forms. Let $W$ denote the potential $\frac{1}{n+1} x^{n+1}$. For the category $MF(W)$ of matrix factorizations of $W$ we prove that there exists a unique, up to nonzero constant, categorical primitive form. The corresponding genus zero categorical GromovWitten invariants of $MF(W)$ are shown to match with the invariants defined through unfolding of singularities of $W$.
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In this paper, we prove a central limit theorem and a moderate deviation principle for a perturbed stochastic CahnHilliard equation defined on [0, T]x [0, \pi]^d, with d \in {1,2,3}. This equation is driven by a spacetime white noise. The weak convergence approach plays an important role.
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The oriented chromatic polynomial of a oriented graph outputs the number of oriented $k$colourings for any input $k$. We fully classify those oriented graphs for which the oriented graph has the same chromatic polynomial as the underlying simple graph, closing an open problem posed by Sopena. We find that such oriented graphs admit a forbidden subgraph characterization, and such graphs can be both identified and constructed in polynomial time. We study the analytic properties of this polynomial and show that there exist oriented graphs which have chromatic polynomials have roots, including negative real roots, that cannot be realized as the root of any chromatic polynomial of a simple graph.
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We develop a probabilistic algorithm for computing elimination ideals of likelihood equations, which is for larger models by far more efficient than directly computing Groebner bases or the interpolation method proposed in the first author's previous work. The efficiency is improved by a theoretical result showing that the sum of data variables appears in most coefficients of the generator polynomial of elimination ideal. Furthermore, applying the known structures of Newton polytopes of discriminants, we can also efficiently deduce discriminants of the elimination ideals. For instance, the discriminants of 3 by 3 matrix model and one JukesCantor model in phylogenetics (with sizes over 30 GB and 8 GB text files, respectively) can be computed by our methods.
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The concept of formal duality was proposed by Cohn, Kumar and Sch\"urmann, which reflects an unexpected symmetry among energyminimizing periodic configurations. This formal duality was later on translated into a purely combinatorial property by Cohn, Kumar, Reiher and Sch\"urmann, where the corresponding combinatorial object was called formally dual pair. Almost all known examples of primitive formally dual pairs satisfy that the two subsets have the same size. Indeed, prior to this work, there is only one known example having subsets with unequal sizes in $\mathbb{Z}_2 \times \mathbb{Z}_4^2$. Motivated by this example, we propose a lifting construction framework and a recursive construction framework, which generate new primitive formally dual pairs from known ones. As an application, for $m \ge 2$, we obtain $m+1$ pairwise inequivalent primitive formally dual pairs in $\mathbb{Z}_2 \times \mathbb{Z}_4^{2m}$, which have subsets with unequal sizes.
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This paper introduces assume/guarantee contracts on continuoustime control systems, hereby extending contract theories for discrete systems to certain new model classes and specifications. Contracts are regarded as formal characterizations of control specifications, providing an alternative to specifications in terms of dissipativity properties or setinvariance. The framework has the potential to capture a richer class of specifications more suitable for complex engineering systems. The proposed contracts are supported by results that enable the verification of contract implementation and the comparison of contracts. These results are illustrated by an example of a vehicle following system.
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We study certain structural properties of fine zonotopal tilings, or cubillages, on cyclic zonotopes $Z(n,d)$ of an arbitrary dimension $d$ and their relations to $(d1)$separated collections of subsets of a set $\{1,2,\ldots,n\}$. (Collections of this sort are well known as strongly separated ones when $d=2$, and as chord separated ones when $d=3$.)
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We examine the dynamics of cuttingandshuffling a hemispherical shell driven by alternate rotation about two horizontal axes using the framework of piecewise isometry (PWI) theory. Previous restrictions on how the domain is cutandshuffled are relaxed to allow for nonorthogonal rotation axes, adding a new degree of freedom to the PWI. A new computational method for efficiently executing the cuttingandshuffling using parallel processing allows for extensive parameter sweeps and investigations of mixing protocols that produce a low degree of mixing. Nonorthogonal rotation axes break some of the symmetries that produce poor mixing with orthogonal axes and increase the overall degree of mixing on average. Arnold tongues arising from rational ratios of rotation angles and their intersections, as in the orthogonal axes case, are responsible for many protocols with low degrees of mixing in the nonorthogonalaxes parameter space. Arnold tongue intersections along a fundamental symmetry
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Endtoend learning of communication systems enables joint optimization of transmitter and receiver, implemented as deep neural networkbased autoencoders, over any type of channel and for an arbitrary performance metric. Recently, an alternating training procedure was proposed which eliminates the need for an explicit channel model. However, this approach requires feedback of realvalued losses from the receiver to the transmitter during training. In this paper, we first show that alternating training works even with a noisy feedback channel. Then, we design a system that learns to transmit real numbers over an unknown channel without a preexisting feedback link. Once trained, this feedback system can be used to communicate losses during alternating training of autoencoders. Evaluations over additive white Gaussian noise and Rayleigh blockfading channels show that endtoend communication systems trained using the proposed feedback system achieve the same performance as when trained
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