Special Fibres and Critical Locus for a Pencil of Plane Curve Singularities

We will analyze the relationships between the special fibres of a pencil of plane curve singularities and the Jacobian curve J of (defined by the zero locus of the Jacobian determinant for any fixed basis ). From the results, we find decompositions of J (and of any special fibre of the pencil) in terms of the minimal resolution of . Using these decompositions and the topological type of any generic pair of curves of , we obtain some topological information about J. More precise decompositions for J can be deduced from the minimal embedded resolution of any pair of fibres (not necessarily generic) or from the minimal embedded resolution of all the special fibres.     

On the Diameter of Plane Curves

Recently, differential geometric properties of embedded projective varieties have gained increasing interest. In this note, we consider plane algebraic curves equipped with the Fubini--Study metric from₂ () and give an estimate for the diameter in terms of the degree, initiated in a paper by F. A. Bogomolov.     

Evolutes of Hyperbolic Plane Curves

Abstract We define the notion of evolutes of curves in a hyperbolic plane and establish the relationships between singularities of these subjects and geometric invariants of curves under the action of the Lorentz group. We also describe how we can draw the picture of an evolute of a hyperbolic plane curve in the Poincaré disk.     

计算平面代数曲线亏格上界的符号-数值算法

亏格是代数曲线的重要不变量.文章给出计算一类平面代数曲线亏格上界的符号-数值混合算法.首先通过数值稳定的符号-数值混合算法把代数曲线的定义多项式系统约化到几何对合形式,然后考察奇点的性质.如果曲线的奇点是寻常的,那么由奇点的重数可以计算出代数曲线的亏格;否则算法仅给出亏格的一个上界.     

Convexity and the Average Curvature of Plane Curves

The average curvature of a rectifiable closed curve in R2 is its total absolute curvature divided by its length. If a rectifiable closed curve in R2 is contained in the interior of a convex set D then its average curvature is at least as large as the average curvature of the simple closed curve D which bounds the convex set.     

分片代数曲线交点的结式求法

本文对确定分片代数曲线的二元样条函数的整体表达式中的截断引入参数表示,给出了分片代数曲线交点的结式求法．理论与实例表明,这种算法是有效的．     

关于弹性力学平面问题中的主轴应力坐标

本文中讨论了弹性力学平面问题中由主轴应力曲线构成的正交曲线坐标系上的平衡方程,以及解的特性.同时,认为在弹性力学中还存在另一种构造解的方式,即可通过直接构造主轴应力正交网络获得主轴应力的解.     

Algorithm for the Semigroup of a Space Curve Singularity

The semigroup of values of irreducible space curve singularities is the set of intersection multiplicities among hypersurfaces and the given curve. It is an invariant of the singularity, and for plane curves it characterizes the equisingularity type considered by Zariski. For space curve singularities the semigroup of values is a numerical semigroup and it can not be computed by means of the exponents of any Puiseux parametrization, as in the plane case. We obtain an algorithm for calculating the semigroup of values of a space curve singularity, which determines the generators of the semigroup and the valuation ideals associated with the semigroup. We give a Maple version of the algorithm.     

平面内判断点与封闭区域关系的快速算法

在诸多研究领域中,判断点是否在封闭多边形区域内是一个非常基本而重要的问题.在分析解决这一问题的常用方法的基础上,以矢量叉积结果的正负号为研究对象,分类讨论特殊情形,提出完整判断点与封闭多边形(包括曲线边)区域关系的算法,然后用LabVIEW编程对算法进行验证并对算法所执行的时间进行测试分析.测试结果显示多边形的凸点数及...     

Cone Adaptation Strategies for a Finite and Exact Cutting Plane Algorithm for Concave Minimization

In this paper we are concerned with pure cutting plane algorithms for concave minimization. One of the most common types of cutting planes for performing the cutting operation in such algorithm is the concavity cut. However, it is still unknown whether the finite convergence of a cutting plane algorithm can be enforced by the concavity cut itself or not. Furthermore, computational experiments have shown that concavity cuts tend to become shallower with increasing iteration. To overcome these problems we recently proposed a procedure, called cone adaptation, which deepens concavity cuts in such a way that the resulting cuts have at least a certain depth with 0, where is independent of the respective iteration, which enforces the finite convergence of the cutting plane algorithm. However, a crucial element of our proof that these cuts have a depth of at least was that we had to confine ourselves to -global optimal solutions, where is a prescribed strictly positive constant. In this paper we examine possible ways to ensure the finite convergence of a pure cutting plane algorithm for the case where = 0.     

Surfaces with pg = 2, K2 = 3 and a pencil of curves of genus 2

We classify minimal smooth surfaces of general type with K ² = 3, p _g = 2 which admit a fibration of curves of genus 2.We prove that they form an irreducible set of dimension 22 in their moduli space.      

Extension of the Leray-Schauder degree for abstract Hammerstein type mappings

We introduce a new extension of the classical Leray-Schauder topological degree in a real separable reflexive Banach space. The new class of mappings for which the degree will be constructed is obtained essentially by replacing the compact perturbation by a composition of mappings of monotone type. It turns out that the class contains the Leray-Schauder type maps as a proper subclass. The new class is not convex thus preventing the free application of affine homotopies. However, there exists a large class of admissible homotopies including subclass of affine ones so that the degree can be effectively used. We shall construct the degree and prove that it is unique. We shall generalize the Borsuk theorem of the degree for odd mappings and show that the ‘principle of omitted rays’ remains valid. To illuminate the use of the new degree we shall briefly consider the solvability of abstract Hammerstein type equations and variational inequalities.     

On S-Shaped Bifurcation Curves for a Class of Perturbed Semilinear Equations

By making use of bifurcation analysis and continuation method, the authors discuss the exact number of positive solutions for a class of perturbed equations. The nonlinearities concerned are the so-called convex-concave functions and their behaviors may be asymptotic sublinear or asymptotic linear. Moreover, precise global bifurcation diagrams are obtained.     

An Algorithm for Computing the Best Convex Contrast Curve of Two Bivariate Samples

Abstract

Let (x ₁, y ₁),…, (x _n, y _n) be a sample of points in , consisting of two subsamples (x ₁, y ₁),…, (x _n1, y _n1) and (x _n1+1, y _n1+1),…, (x _n, y _n), where n = n ₁ + n ₂. We consider the problem of separating the two subsamples by a convex contrast curve k…that is, a real-valued convex function x → k(x). For given curve k we consider the relative frequency p ₁ of points of the first sample above the graph of k similarly p ₂. The goal is to choose k such that the difference in relative frequency p ₁ – p ₂ becomes maximal. This maximal value can be regarded as a generalized one-sided Kolmogorov-Smirnov test statistic , where p ₁(A) = (1/n ₁)#{i ≤ n ₁ : (xi, y _i) ∈ A}, p ₂(A) = (1/n ₂#{n ₁ + 1 ≤ i ≤ n : (x _i, y _i) ∈ A} and is the class of all epigraphs {(x y) : k(x) ≤ y} of convex functions k. The standard Kolmogorov-Smirnov test statistic corresponds to the class consisting of all sets —that is, epigraphs of constant functions. Test statistics of this form arise in nonparametric analysis of covariance where the regression function is assumed to be convex. In this article we give a recursive relation and an algorithm based on it to compute the value KS and an optimal convex contrast curve in O(n ³) steps. The convexity assumptions on the sets of and on the nonparametric regression function are interrelated; this is explained in the large sample situation where n ₁ Λ n ₂ → + ∞.     

An Optimal Deterministic Algorithm for Computing the Diameter of a Three-Dimensional Point Set

We describe a deterministic algorithm for computing the diameter of a finite set of points in R ³ , that is, the maximum distance between any pair of points in the set. The algorithm runs in optimal time O(nlog n) for a set of n points. The first optimal, but randomized, algorithm for this problem was proposed more than 10 years ago by Clarkson and Shor [11] in their ground-breaking paper on geometric applications of random sampling. Our algorithm is relatively simple except for a procedure by Matoušek [25] for the efficient deterministic construction of epsilon-nets. This work improves previous deterministic algorithms by Ramos [31] and Bespamyatnikh [7], both with running time O(nlog ² n) . The diameter algorithm appears to be the last one in Clarkson and Shor's paper that up to now had no deterministic counterpart with a matching running time. Received May 10, 2000, and in revised form November 3, 2000. Online publication June 22, 2001.     

拟线性可化约的双曲型方程组的奇性分析

In this paper we investigate the formation of singularities of hyperbolic systems. Employing the method of parametric coordinates and the existence of the solution of the blow-up system, we prove that the blow-up of classic solutions is due to the envelope of characteristics of the same family, analyze the geometric properties of the envelope of characteristics and estimate the blowup rates of the solution precisely.     

An Efficient Algorithm for Computing the HHSVM and Its Generalizations

The hybrid Huberized support vector machine (HHSVM) has proved its advantages over the ?₁ support vector machine (SVM) in terms of classification and variable selection. Similar to the ?₁ SVM, the HHSVM enjoys a piecewise linear path property and can be computed by a least-angle regression (LARS)-type piecewise linear solution path algorithm. In this article, we propose a generalized coordinate descent (GCD) algorithm for computing the solution path of the HHSVM. The GCD algorithm takes advantage of a majorization–minimization trick to make each coordinatewise update simple and efficient. Extensive numerical experiments show that the GCD algorithm is much faster than the LARS-type path algorithm. We further extend the GCD algorithm to solve a class of elastic net penalized large margin classifiers, demonstrating the generality of the GCD algorithm. We have implemented the GCD algorithm in a publicly available R package gcdnet.     

Symmetries of Field Theories on the Noncommutative Plane

We report new developments concerning the symmetry properties and their actions on special solutions allowed by certain field theory models on the noncommutative plane. In particular, we seek Galilean-invariant models. The analysis indicates that this requirement strongly restricts the admissible interactions. Moreover, if a scalar field is coupled to a gauge field, then a geometric phase emerges for vortexlike solutions transformed by Galilean boosts.__________Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 144, No. 1, pp. 64–73, July, 2005.     

An Algorithm for Computing Fundamental Solutions of Difference Operators

We propose an FFT-based algorithm for computing fundamental solutions of difference operators with constant coefficients. Our main contribution is to handle cases where the symbol has zeros.