Linear Change Of Coordinates Research Articles

Classifying Abelian Groups Through Acyclic Matchings

AbstractThe inquiry into identifying sets of monomials that can be eliminated from a generic homogeneous polynomial via a linear change of coordinates was initiated by E. K. Wakeford. This linear algebra problem prompted C. K. Fan and J. Losonczy to introduce the notion of acyclic matchings in the additive group $$\mathbb {Z}^n$$ Z n , subsequently extended to abelian groups by the latter author. Alon, Fan, Kleitman, and Losonczy established the acyclic matching property for $$\mathbb {Z}^n$$ Z n . This note aims to classify all abelian groups with respect to the acyclic matching property.

Toric degenerations of low-degree hypersurfaces

AbstractWe show that a sufficiently general hypersurface of degree d in $\mathbb {P}^n$ admits a toric Gröbner degeneration after linear change of coordinates if and only if $d\leq 2n-1$ .

Real Normal Form of a Binary Polynomial at a Second-Order Critical Point

A real polynomial in two variables is considered. Its expansion near the zero critical point begins with a third-degree form. The simplest forms to which this polynomial is reduced with the help of invertible real local analytic changes of coordinates are found. First, for the cubic form, normal forms are obtained using linear changes of coordinates. Altogether, there are three of them. Then three nonlinear normal forms are obtained for the complete polynomial. Simplification of the calculation of a normal form is proposed. A meaningful example is given.

Lower bounds on the F-pure threshold and extremal singularities

We prove that if f f is a reduced homogeneous polynomial of degree d d , then its F F -pure threshold at the unique homogeneous maximal ideal is at least 1 d − 1 \frac {1}{d-1} . We show, furthermore, that its F F -pure threshold equals 1 d − 1 \frac {1}{d-1} if and only if f ∈ m [ q ] f\in \mathfrak m^{[q]} and d = q + 1 d=q+1 , where q q is a power of p p . Up to linear changes of coordinates (over a fixed algebraically closed field), we classify such “extremal singularities”, and show that there is at most one with isolated singularity. Finally, we indicate several ways in which the projective hypersurfaces defined by such forms are “extremal”, for example, in terms of the configurations of lines they can contain.

Discrete max-linear Bayesian networks

Discrete max-linear Bayesian networks are directed graphical models specified by the same recursive structural equations as max-linear models but with discrete innovations. When all of the random variables in the model are binary, these models are isomorphic to the conjunctive Bayesian network (CBN) models of Beerenwinkel, Eriksson, and Sturmfels. Many of the techniques used to study CBN models can be extended to discrete max-linear models and similar results can be obtained. In particular, we extend the fact that CBN models are toric varieties after linear change of coordinates to all discrete max-linear models.

Computing the resolution regularity of bi-homogeneous ideals

We present an effective method to compute the resolution regularity (vector) of bi-homogeneous ideals. For this purpose, we first introduce the new notion of an x-Pommaret basis and describe an algorithm to compute a linear change of coordinates for a given bi-homogeneous ideal such that the new ideal obtained after performing this change possesses a finite x-Pommaret basis. Then, we show that the x-component of the bi-graded regularity of a bi-homogeneous ideal is equal to the x-degree of its x-Pommaret basis (after performing the mentioned linear change of variables). Finally, we introduce the new notion of an ideal in x-quasi stable position and show that a bi-homogeneous ideal has a finite x-Pommaret basis iff it is in x-quasi stable position.

On a center-of-mass system of coordinates for symmetric classical and quantum many-body problems

In the context of classical or quantum many-body problems involving identical bodies, a linear change of coordinates can be constructed with the properties that it includes the center-of-mass as one of the new coordinates and preserves the inherent permutation symmetry of both the Hamiltonian and the admissible states. This has advantages over the usual system of Jacobi coordinates in the study of many-body problems for which permutation symmetry of the bodies plays an important role. This paper contains the details of the construction of this system and the proof that these properties uniquely determine it up to trivial modifications. Examples of applications to both classical and quantum problems are explored, including a generalization to problems involving groups of different species of bodies.

Study of Amplitude Control and Dynamical Behaviors of a Memristive Band Pass Filter Circuit

The existence of a partial and total amplitude control in a band pass filter circuit with a memristor is explained theoretically and confirmed in simulations. A linear change of coordinates is derived to develop a simple three-parameter model of the circuit. Dynamical phenomena observed in the circuit are analyzed.

Isochronicity for trivial quintic and septic planar polynomial Hamiltonian systems

In this paper we completely characterize trivial polynomial Hamiltonian isochronous centers of degrees $5$ and $7$. Precisely, we provide simple formulas, up to linear change of coordinates, for the Hamiltonians of the form $H = \left(f_1^2 + f_2^2 \right)/2$, where $f = (f_1, f_2): \mathbb{R}^2\to \mathbb{R}^2$ is a polynomial map with $\det D f = 1$, $f(0,0) = (0,0)$ and the degree of $f$ is $3$ or $4$.

Counting and characterising functions with \u201cfast points\u201d for differential attacks

Higher order derivatives have been introduced by Lai in a cryptographic context. A number of attacks such as differential cryptanalysis, the cube and the AIDA attack have been reformulated using higher order derivatives. Duan and Lai have introduced the notion of “fast points” of a polynomial function f as being vectors a so that computing the derivative with respect to a decreases the total degree of f by more than one. This notion is motivated by the fact that most of the attacks become more efficient if they use fast points. Duan and Lai gave a characterisation of fast points and Duan et al. gave some results regarding the number of functions with fast points in some particular cases. We firstly give an alternative characterisation of fast points and secondly give an explicit formula for the number of functions with fast points for any given degree and number of variables, thus covering all the cases left open in Duan et al. Our main tool is an invertible linear change of coordinates which transforms the higher order derivative with respect to an arbitrary set of linearly independent vectors into the higher order derivative with respect to a set of vectors in the canonical basis. Finally we discuss the cryptographic significance of our results.

Aspects of the zeta function originating from pseudodifferential analysis

Pseudodifferential analysis helps linking the one-dimensional and two-dimensional analyses in more than one way. Taking benefit from special features of the two-dimensional case, in particular the fact that homogeneous distributions, invariant under the action by linear changes of coordinates of \(SL(2,{\mathbb Z})\), are essentially disguised versions of nonholomorphic modular forms, we are led to introducing interesting two-dimensional distributions and some associated one-dimensional parts. This results in a collection of necessary and sufficient conditions for the Riemann hypothesis to hold, some of which, but not all, are of a more or less classical type.

A genericity theorem for algebraic stacks and essential dimension of hypersurfaces

We compute the essential dimension of the functors Forms _{n,d} and Hypersurf _{n, d} of equivalence classes of homogeneous polynomials in n variables and hypersurfaces in \mathbb P^{n-1} , respectively, over any base field k of characteristic 0 . Here two polynomials (or hypersurfaces) over K are considered equivalent if they are related by a linear change of coordinates with coefficients in K . Our proof is based on a new Genericity Theorem for algebraic stacks, which is of independent interest. As another application of the Genericity Theorem, we prove a new result on the essential dimension of the stack of (not necessarily smooth) local complete intersection curves.

The geometry of border bases

In this paper we continue the study of the border basis scheme we started in Kreuzer and Robbiano (2008) [16]. The main topic is the construction of various explicit flat families of border bases. To begin with, we cover the punctual Hilbert scheme Hilb μ ( A n ) by border basis schemes and work out the base changes. This enables us to control flat families obtained by linear changes of coordinates. Next we provide an explicit construction of the principal component of the border basis scheme, and we use it to find flat families of maximal dimension at each radical point. Finally, we connect radical points to each other and to the monomial point via explicit flat families on the principal component.

Mass Transportation with LQ Cost Functions

We study the optimal transport problem in the Euclidean space where the cost function is given by the value function associated with a Linear Quadratic minimization problem. Under appropriate assumptions, we generalize Brenier's Theorem proving existence and uniqueness of an optimal transport map. In the controllable case, we show that the optimal transport map has to be the gradient of a convex function up to a linear change of coordinates. We give regularity results and also investigate the non-controllable case.

Topology of real algebraic space curves

In this paper we give a new projection-based algorithm for computing the topology of a real algebraic space curve given implicitly by a set of equations. Under some genericity conditions, which may be reached through a linear change of coordinates, we show that a plane projection of the given curve, together with a special polynomial in the ideal of the curve contains all the information needed to compute its topological shape. Our method is also designed in such a way to exploit important particular cases such as complete intersection curves or curves contained in nonsingular surfaces.

Essential dimension of cubics

In this paper, we compute the essential dimension of the functor of cubics in three variables up to linear changes of coordinates when the base field has characteristic different from 2 and 3. For this, we use canonical pencils of cubics, Galois descent techniques, and the basic material on essential dimension developed in [G. Berhuy, G. Favi, Doc. Math. 8 (2003) 279–330] which is based on Merkurjev's notes [Essential dimension, 1999].

Real Factorization of Multivariate Polynomials with Integer Coefficients

In the recent papers, a new efficient probabilistic semi-numerical absolute (i.e., complex) factorization algorithm for multivariate polynomials with integer coefficients is given. It is based on a simple property of the monomials arising after a generic linear change of coordinates for bivariate polynomials and on a deep result of complex algebraic geometry. Here, we consider the a priori simpler problem of factorization over the field of reals. We briefly review our algorithm for complex factorization and adapt it to solving the problem on the field of reals. This allows us to spare a significant part of the computations and to improve the range of tractability. The method provides factors with approximative coefficients and eventually exact factors in a suitable real algebraic extension of \(\mathbb{Q}\). Bibliography: 15 titles.

Relations Between the Correlators of the Topological Sigma-Model Coupled to Gravity

We prove a new recursive relation between the correlators ¶ , which together with known relations allows one to express all of them through the full system of Gromov–Witten invariants in the sense of Kontsevich–Manin and the intersection indices of tautological classes on , effectively calculable in view of earlier results due to Mumford, Kontsevich, Getzler, and Faber. This relation shows that a linear change of coordinates of the big phase space transforms the potential with gravitational descendants to another function defined completely in terms of the Gromov–Witten correspondence and the intersection theory on . We then extend the formalism of gravitational descendants from quantum cohomology to more general Frobenius manifolds and Cohomological Field Theories.

Isochronous oscillations for cubic systems

Planar vector fieldsẋ = -y + P₃(x,y)ẏ = x + q₃(x, y).with a center non necessarily at the origin are considered, where p₃ and q₃ are homogeneous polynomials of degree 3. We are concerned with the behavior of the periods of the periodic solutions near the center, and in determining when the center is isochronous, i.e., when all periodic solutions have the same period. It is proved that, modulus a linear change of coordinates, there are only four systems which have an isochronous center. Each of them has an isochronous center at the origin, and its other centers are also isochronous but not necessarily with the same period. Also the maximal weakness of the non isochronous centers, is obtained.

Time-Domain Solutions of Oja's Equations

Oja's equations describe a well-studied system for unsupervised Hebbian learning of principal components. This paper derives the explicit time-domain solution of Oja's equations for the single-neuron case. It also shows that, under a linear change of coordinates, these equations are a gradient system in the general multi-neuron case. This latter result leads to a new Lyapunov-like function for Oja's equations.