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 3-Pfister Number of Quadratic Forms

For a field F of characteristic different from 2, containing a square root of -1, endowed with an F^×2-compatible valuation v such that the residue field has at most two square classes, we use a combinatorial analogue of the Witt ring of F to prove that an anisotropic quadratic form over F with even dimension d, trivial discriminant, and Hasse–Witt invariant can be written in the Witt ring as the sum of at most (d²)/8 3-fold Pfister forms.     

On the Representation of Numbers by the Direct Sums of Some Binary Quadratic Forms

The systems of bases are constructed for the spaces of cusp forms and . Formulas are obtained for the number of representations of a positive integer by the sum of k binary quadratic forms of the kind , of the kind and of the kind .     

On the Representation of Numbers by Positive Diagonal Quadratic Forms with Five Variables of Level 16

A general formula is derived for the number of representations r(n; f) of a natural number n by diagonal quadratic forms f with five variables of level 16. For f belonging to one-class series, r(n; f) coincides with the sum of a singular series, while in the case of a many-class series an additional term is required, for which the generalized theta-function introduced by T. V. Vepkhvadze [4] is used.     

Energy and Quadratic Invariants Preserving Methods for Hamiltonian Systems with Holonomic Constraints

We introduce a new class of parametrized structure--preserving partitioned Runge-Kutta ($\alpha$-PRK) methods for Hamiltonian systems with holonomic constraints. The methods are symplectic for any fixed scalar parameter $\alpha$, and are reduced to the usual symplectic PRK methods like Shake-Rattle method or PRK schemes based on Lobatto IIIA-IIIB pairs when $\alpha=0$. We provide a new variational formulation for symplectic PRK schemes and use it to prove that the $\alpha$-PRK methods can preserve the quadratic invariants for Hamiltonian systems subject to holonomic constraints. Meanwhile, for any given consistent initial values $(p_{0}, q_0)$ and small step size $h>0$, it is proved that there exists $\alpha^*=\alpha(h, p_0, q_0)$ such that the Hamiltonian energy can also be exactly preserved at each step. Based on this, we propose some energy and quadratic invariants preserving $\alpha$-PRK methods. These $\alpha$-PRK methods are shown to have the same convergence rate as the usual PRK methods and perform very well in various numerical experiments.     

用正交变换化实二次型为标准形的同步求解问题

作为《关于矩阵的特征值与特征向量同步求解问题》的续篇,利用其给出的方法,证明了新的定理.通过对实对称矩阵进行行列互逆变换,同步求出二次型的标准形及正交变换阵,简化了复杂的施密特正交化法,较好地解决了二次型标准形与正交变换阵同步求解问题.     

Asymptotic Expansions in Non-central Limit Theorems for Quadratic Forms

We consider quadratic forms of the type

Asymptotic Distribution of Quadratic Forms and Applications

We consider the quadratic formsQ X _j X _k+ (X _j ² -E X _j ² )where X _j are i.i.d. random variables with finite sixth moment. For a large class of matrices (a _jk ) the distribution of Q can be approximated by the distribution of a second order polynomial in Gaussian random variables. We provide optimal bounds for the Kolmogorov distance between these distributions, extending previous results for matrices with zero diagonals to the general case. Furthermore, applications to quadratic forms of ARMA-processes, goodness-of-fit as well as spacing statistics are included.     

Connectivity of Level Sets of Quadratic Forms and Hausdorff-Toeplitz Type Theorems

Main theorem: for an arbitrary linear operator A : X X in a complex pre-Hilbert space X, dim X 3, all level sets { x X : = ,x = 1} are connected. This fails if dim X=2 and int W(A) where W(A) is the numerical range. The main theorem implies the known result on convexity of generalized numerical range of three Hermitian operators.     

Singularly Perturbed Hamiltonians of a Quantum Rayleigh Gas Defined as Quadratic Forms

We consider a class of singular, zero-range perturbations of the quantum Hamiltonian of a system consisting of a test particle and N harmonic oscillators (Rayleigh gas). Using the theory of quadratic forms we construct the self-adjoint and bounded from below perturbed Hamiltonian and we give representation formulas for the resolvent and the unitary group. The one-dimensional, two-dimensional and three-dimensional cases are discussed. Mathematics Subject Classifications (2000) 47A07, 47N50.Gianfausto DellAntonio: On leave from Dipartimento di Matematica, Università di Roma La Sapienza, Italy     

Regular Splitting and Potential Reduction Method for Solving Quadratic Programming Problem with Box Constraints

A regular splitting and potential reduction method is presented for solving a quadratic programming problem with box constraints (QPB) in this paper. A general algorithm is designed to solve the QPB problem and generate a sequence of iterative points. We show that the number of iterations to generate an e-minimum solution or an e-KKT solution by the algorithm is bounded by O( nlog(1 )), and the total running time is bounded by O(n2(n logn log1/ε)(n/εlog1/ε logn)) arithmetic operations.     

The Karoubi Tower and K-Theory Invariants of Hermitian Forms

By the use of the Karoubi Tower diagram we generalize the classical invariants of quadratic forms. Similar to Quillen's higher K-theory generalization of the classical K-theory groups, these invariants are an extension of the classical invariants by the use of homotopy theory. The iterated forgetful maps in the Karoubi Tower are KR valued and yield a generalization of the standard (rank, discriminant and total Hasse–Witt) invariants of quadratic forms in two directions. First, we get invariants of all degrees. Second, these invariants are defined for every Hermitian ring. They yield and generalize the Clifford invariant in the case of a field of characteristic different from 2, or in the case of an arithmetic Dedekind domain containing .     

The Automorphism Group and the Convex Subgraphs of the Quadratic Forms Graph in Characteristic 2

We determine the automorphism group and the convex subgraphs of the quadratic forms graph Quad(n,q),q even.A. Munemasa: A part of this research was completed during this author's visit at the Institute for System Analysis, Moscow, as a Heizaemon Honda fellow of the Japan Association for Mathematical SciencesD.V. Pasechnik: A part of this research was completed when this author held a position at the Institute for System Analysis, MoscowS.V. Shpectorov: A part of this research was completed during this author's visit at the University of Technology, Eindhoven     

On the Number of Representations of Integers by Quadratic Forms in Twelve Variables

A way of finding exact explicit formulas for the number of representations of positive integers by quadratic forms in 12 variables with integral coefficients is suggested.     

Quadratic forms and Pfister neighbors in characteristic 2

We study Pfister neighbors and their characterization over fields of characteristic , where we include the case of singular forms. We give a somewhat simplified proof of a theorem of Fitzgerald which provides a criterion for when a nonsingular quadratic form is similar to a Pfister form in terms of the hyperbolicity of this form over the function field of a form which is dominated by . From this, we derive an analogue in characteristic of a result by Knebusch saying that, in characteristic , a form is a Pfister neighbor if its anisotropic part over its own function field is defined over the base field. Our result includes certain cases of singular forms, but we also give examples which show that Knebusch's result generally fails in characteristic for singular forms. As an application, we characterize certain forms of height in the sense of Knebusch whose quasi-linear parts are of small dimension. We also develop some of the basics of a theory of totally singular quadratic forms. This is used to give a new interpretation of the notion of the height of a standard splitting tower as introduced by the second author in an earlier paper.

     

Small Solutions of Quadratic Diophantine Equations

We consider quadratic diophantine equations of the shape for a polynomial Q(X₁, ..., X_s) Z[X₁, ..., X_s] of degree 2.Let H be an upper bound for the absolute values of the coefficientsof Q, and assume that the homogeneous quadratic part of Q isnon-singular. We prove, for all s 3, the existence of a polynomialbound _s(H) with the following property: if equation (1) hasa solution x Z^s at all, then it has one satisfying For s = 3 and s = 4 no polynomial bounds _s(H) were previouslyknown, and for s 5 we have been able to improve existing boundsquite significantly. 2000 Mathematics Subject Classification11D09, 11E20, 11H06, 11P55.     

Invariants of trace forms in odd characteristic and authentication codes

We complete A. Klapper's work on the invariant of a one-term trace form over a finite field of odd characteristic. We apply this to computing the probability of a successful impersonation attack on an authentication code proposed by C. Ding et al. (2005).     

Association Schemes of Quadratic Forms and Symmetric Bilinear Forms

Let X _n and Y _n be the sets of quadratic forms and symmetric bilinear forms on an n-dimensional vector space V over , respectively. The orbits of GL _n( ) on X _n × X _n define an association scheme Qua(n, q). The orbits of GL _n( ) on Y _n × Y _n also define an association scheme Sym(n, q). Our main results are: Qua(n, q) and Sym(n, q) are formally dual. When q is odd, Qua(n, q) and Sym(n, q) are isomorphic; Qua(n, q) and Sym(n, q) are primitive and self-dual. Next we assume that q is even. Qua(n, q) is imprimitive; when (n, q) (2,2), all subschemes of Qua(n, q) are trivial, i.e., of class one, and the quotient scheme is isomorphic to Alt(n, q), the association scheme of alternating forms on V. The dual statements hold for Sym(n, q).     

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).     

二次型之比服从F—分布的充分必要条件

考察F－分布的密度和矩，本文给出了正态随机向量二次型之比服从F－分布的充分必要条件，进而给出了椭球等高随机向量二次型之比服从F分布的充分必要条件．作为应用，我们减弱了传统F－检验中对两简单子样独立性的要求．