Quadratic residues and non-residues for infinitely many Piatetski-Shapiro primes

In this paper, we prove a quantitative version of the statement that every nonempty finite subset of N+ is a set of quadratic residues for infinitely many primes of the form [nc] with 1 ≤ c ≤243/205. Correspondingly, we can obtain a similar result for the case of quadratic non-residues under reasonable assumptions. These results generalize the previous ones obtained by Wright in certain aspects.     

A Multilevel Search Algorithm for the Maximization of Submodular Functions Applied to the Quadratic Cost Partition Problem

Maximization of submodular functions on a ground set is a NP-hard combinatorial optimization problem. Data correcting algorithms are among the several algorithms suggested for solving this problem exactly and approximately. From the point of view of Hasse diagrams data correcting algorithms use information belonging to only one level in the Hasse diagram adjacent to the level of the solution at hand. In this paper, we propose a data correcting algorithm that looks at multiple levels of the Hasse diagram and hence makes the data correcting algorithm more efficient. Our computations with quadratic cost partition problems show that this multilevel search effects a 8- to 10-fold reduction in computation times, so that some of the dense quadratic partition problem instances of size 500, currently considered as some of the most difficult problems and far beyond the capabilities of current exact methods, are solvable on a personal computer working at 300 MHz within 10 min.     

Consecutive numbers with the same Legendre symbol

Let be an odd prime, and be a complete set of residues . The goal of the paper is to determine all the values of such that or , where is the Legendre symbol.

     

Quadratic and Symmetric Bilinear Compositions of Quadratic Forms Over Commutative Rings

Over commutative rings in which 2 is a zero-divisor, to compose a quadratic form with symmetric bilinear forms or with quadratic forms is not quite the same. In this article, the relation between the two classes of compositions is clarified and the results applied to find the ranks of minimal compositions.     

On the Characterization of Quadratic Splines

A quadratic spline is a differentiable piecewise quadratic function. Many problems in the numerical analysis and optimization literature can be reformulated as unconstrained minimizations of quadratic splines. However, only special cases of quadratic splines have been studied in the existing literature and algorithms have been developed on a case-by-case basis. There lacks an analytical representation of a general or even convex quadratic spline. The current paper fills this gap by providing an analytical representation of a general quadratic spline. Furthermore, for a convex quadratic spline, it is shown that the representation can be refined in the neighborhood of a nondegenerate point and a set of nondegenerate minimizers. Based on these characterizations, many existing algorithms for specific convex quadratic splines are also finitely convergent for a general convex quadratic spline. Finally, we study the relationship between the convexity of a quadratic spline function and the monotonicity of the corresponding linear complementarity problem. It is shown that, although both conditions lead to easy solvability of the problem, they are different in general.This project was initiated when the first author was visiting the Technical University of Denmark and Erasmus University. The visit was partially funded by the Danish Natural Science Research Council.     

On the Limit Cycles of Quadratic Differential Systems

In this paper we give the necessary and sufficient conditions for all finite critical points of quadratic differential systems to be weak foci, and solve an open problem proposed by Yanquian Ye. Received January 11, 1999, Revised October 10, 2000, Accepted March 5, 2001     

Global Optimization of a Quadratic Functional with Quadratic Equality Constraints, Part 2

In this paper, we investigate a constrained optimization problem with a quadratic cost functional and two quadratic equality constraints. It is assumed that the cost functional is positive definite and that the constraints are both feasible and regular (but otherwise they are unrestricted quadratic functions). Thus, the existence of a global constrained minimum is assured. We develop a necessary and sufficient condition that completely characterizes the global minimum cost. Such a condition is of essential importance in iterative numerical methods for solving the constrained minimization problem, because it readily distinguishes between local minima and global minima and thus provides a stopping criterion for the computation. The result is similar to one obtained previously by the authors. In the previous result, we gave a characterization of the global minimum of a constrained quadratic minimization problem in which the cost functional was an arbitrary quadratic functional (as opposed to positive-definite here) and the constraints were at least positive-semidefinite quadratic functions (as opposed to essentially unrestricted here).     

Explicit Solutions of Quadratic FBSDEs Arising From Quadratic Term Structure Models

We provide explicit solutions of certain forward-backward stochastic differential equations (FBSDEs) with quadratic growth. These particular FBSDEs are associated with quadratic term structure models of interest rates and characterize the zero-coupon bond price. The results of this paper are naturally related to similar results on affine term structure models of Hyndman (Math. Financ. Econ. 2(2):107–128, 2009) due to the relationship between quadratic functionals of Gaussian processes and linear functionals of affine processes. Similar to the affine case a sufficient condition for the explicit solutions to hold is the solvability in a fixed interval of Riccati-type ordinary differential equations. However, in contrast to the affine case, these Riccati equations are easily associated with those occurring in linear-quadratic control problems. We also consider quadratic models for a risky asset price and characterize the futures price and forward price of the asset in terms of similar FBSDEs. An example is considered, using an approach based on stochastic flows that is related to the FBSDE approach, to further emphasize the parallels between the affine and quadratic models. An appendix discusses solvability and explicit solutions of the Riccati equations.     

Approximation of the Quadratic Set Covering problem

We study in this article the polynomial approximation properties of the Quadratic Set Covering problem. This problem, which arises in many applications, is a natural generalization of the usual Set Covering problem. We show that this problem is very hard to approximate in the general case, and even in classical subcases (when the size of each set or when the frequency of each element is bounded by a constant). Then we focus on the convex case and give both positive and negative approximation results. Finally, we tackle the unweighted version of this problem.     

On the Conditions of a Center and General Integrals of Quadratic Differential Systems

We give the general integral of quadratic differential system with center in two cases under the Chinese classification. Project supported by the National Natural Science Foundation of China and Natural Science Foundation of Jiangsu Province Education Commission     

Quadratic programming and combinatorial minimum weight product problems

We present a fully polynomial time approximation scheme (FPTAS) for minimizing an objective (a ^T x + γ)(b ^T x + δ) under linear constraints A x ≤ d. Examples of such problems are combinatorial minimum weight product problems such as the following: given a graph G = (V,E) and two edge weights find an s − t path P that minimizes a(P)b(P), the product of its edge weights relative to a and b.      

二次微分系统的中心条件和通积分

本文给出在中国分类之下二次微分系统有中心时两种情况的通积分.     

二次李超三系的分解定理

讨论了二次李超三系的唯一分解,得到了二次李超三系分解为非退化不可约阶化理想的分解定理.     

Quadratic residues and the distribution of prime numbers

D. Shanks [11] has given a heuristical argument for the fact that there are “more” primes in the non-quadratic residue classes modq than in the quadratic ones. In this paper we confirmShanks' conjecture in all casesq<25 in the following sense. Ifl ₁ is a quadratic residue,l ₂ a non-residue modq, ε(n, q, l ₁,l ₂) takes the values +1 or ?1 according ton?l ₁ orl ₂ modq, then $$\mathop {\lim }\limits_{x \to \infty } \sum\limits_p {\varepsilon (p,q,l_1 ,l_2 )} \log pp^{ - \alpha } \exp ( - (\log p)^2 /x) = - \infty$$ for 0≤α<1/2. In the general case the same holds, if all zeros ?=β+yγ of allL(s, χ modq),q fix, satisfy the inequality β²?γ²<1/4.     

On the p 2-Rank of Tame Kernels of Quadratic Fields

For any odd prime p, we prove some results connecting the p²-rank of the tame kernel of a quadratic field F with the p²-rank Cl(𝒪_E1 ), where E₁ is the maximal real subfield of F(ζ_p² ).     

Torelli Theorem for the Moduli Spaces of Rank 2 Quadratic Pairs

Let X be a smooth projective complex curve. We prove that a Torelli type theorem holds, under certain conditions, for the moduli space of α-polystable quadratic pairs on X of rank 2.