海水入浸问题的数值分析

海水入浸问题的数学模型是两个耦合抛物型偏微分方程,其中一个是关于压力的流动方程,另一个是关于浓度的对流扩散方程.压力方程由标准有限元方法逼近,浓度方程则用特征有限元方法逼近.在扩散项系数半正定的情形得到逼近解的次优L2 模误差估计.     

一类非线性Schrdinger方程的解

本文讨论这样一类非线性Schrdinger方程:其中k,v是常数,v>O;Ω■R~2;u(x,t)是复值未知函数;u_0是初值,已知。 给出1.方程整体解的存在性和解的估计;2.在Ω是R~2中的外区域情况下,当t→∞时解的渐近性。     

Kantorovich型Meyer-K(o)nig-Zeller算子的点态逼近定理

1引 言 1960年Meyer-K(o)nig W.和Zeller K.在[6]中提出了Meyer-K(o)nig-Zeller算子 Mn(f,x)=∞∑k=0f(k/(n+k))mn,k(x),0≤x＜1,Mn(f,1):=f(1),mn,k(x)=(n+kk)xk(1-x)n+1,在[1,2,5,7,9,10,12]中对于此算子的逼近性质及各种修正了的Meyer-K(o)nig-Zeller算子作了研究,其中重要的变形是Kantorovich型的积分算子： M*n(f;x)=∞∑k=0((n+k)(n+k+1))/n∫(k+1)/(n+k+1)k/(n+k)f(u)dumn,k(x),x∈[0,),其中Mn(f,1)：＝f(1),mn,k(x)＝(n+kk)xk(1+x)n+1,mn,-1(x)：=0. V.Totik在[8]中给出了M*n(f;x)的Lp-逼近(1≤p＜∞),王建力在[11]研究了其加权Lp-逼近(1≤p＜∞).本文引进新的K+泛函,利用Ditzian-Totik模ω2ψ(f,t)研究了该算子的点态逼近性质,得到了它的逼近正、逆及等价定理.     

论判别分析方法的最优选择

1引言 判别分析的基本问题是:在多变量观测值的基础上,把一个未知对象划入两个或多个种类中的某一类.具体地说,就是:设有k个m维总体G1,…,Gk,它们的均值和协差阵分别为μ(1),…,μ(k)和V(1),…,V(k).今从这k个总体中分别抽取了n1,…,nk个样本,记为x(1)(1),…,x(a1)(1);…;x(1)(k),…,x(nk)(k)这个样本集合通常称为训练样本,由此得观测数据矩阵对试验样本,即待判的未知样本集合中的样本要判别它来自哪个总体. 判别分析的内容十分丰富,这方面的综述性文献有[1]、[2],[3]等.在国内文献中,文献[4]的第四章介绍的比较全面、具体。虽然判别分析…     

有向图的L(j,k)数的上界

给定正整数j≥k,有向图D的一个L(j,k)-标号是指从V(D)到非负整数集的一个函数f,使得当x在D中邻接到y时|f(x)-f(y)|≥j,当x在D中到y距离为二时|f(x)-f(y)|≥k.f的像元素称为标号.L(j,k)一标号问题就是确定(?)j,k-数(?)j,k(D),这个参数等于(?) max{f(x)|x∈V(D)},这里f取遍D的所有L(j,k)-标号.本文根据有向图的有向着色数及最长有向路的长度来研究(?)j,k-数,证明了:(1)对任何有向着色数为(?)(D)的有向图D,(?)j,k(D)≤((?)(D)-1)j;(2)对任何最长有向路的长度为l的有向图D,如果不含有向圈或者D中最长有向圈长度为l 1,则(?)j,k(D)≤lj.并且这两个界都是可达的.最后我们对l=3的有向图给出了3j-L(j,k)-labelling的一个有效算法.     

非定常线性化Navier-Stokes方程的非协调流线扩散有限元法分析

对非定常线性化Navier-Stokes方程提出了非协调流线扩散有限元方法．用向后Euler格式离散时间,用流线扩散法处理扩散项带来的非稳定性．速度采用不连续的分片线性逼近,压力采用分片常数逼近．得到了离散解的存在唯一性以及在一定范数意义下离散解的稳定性和误差估计．     

关于双曲型方程解的爆破

在RNR+(N2)中考虑非线性双曲型方程 utt-DI(aij(x)Dju)=|u|p-1u.Kato1980年证明了当1<p [SX(]N+1[]N-1[SX)]时,Cauchy问题的解可能在有限时刻爆破.本文使用不同的方法估计, 把Kato的结果改进为1<p<[SX(]N+3[]N-1[SX)].     

非线性逼近的强唯一性

设G是赋范线性空间 E 的子集,x∈E,g_0∈G.称 g_0是 G 对 x 是 q(q>1)阶强唯一最佳逼近乃指:若存在常数 C=C(x)>0,满足‖x-g‖~q≥‖x-g_0‖~q+c‖g-g_0‖~q,(?)g∈G.(1)我们对所有满足(1)式的常数 C 上确界为 x 相对于 G 的强唯一常数,记作 r(x).本文先获得:若 G 是 L_p 或 H~(k,p)(K≥0,2≤p≤∞)的弱拟凸(伪凸、拟凸)集,则 G 对 x∈L_p(H~(k,p))的最佳逼近具有 p 阶强唯一性;然后在一般赋范空间证明了 r(x)相对于 x 是上半连续的.     

一类抛物型方程系数反问题的分裂算法

考虑利用终端时刻的温度u(x,T)=Z_T(x)反演热传导方程u_t-a~2u_(xx) q(x)u=0,x∈(0,1)中的未知系数q(x)的反问题.通过引进变换v(x,t)=(u_t(x,t)/u(x,t))将此非线性不适定问题的求解分解为两步.首先利用输入数据迭代求解一个非线性的正问题(该过程独立于未知系数),得到其迭代解v~(k)(x,t).其次利用q(x)与v(x,t)的关系式求出q(x)的近似解.对提出的反演方法,证明了采用的变换的可行性,得到了原反问题与由变换后的非线性正问题反演q(x)的等价性并且证明了迭代解的收敛性,给出了收敛速度.数值结果表明了该方法的有效性.     

关于非线性微分系统的无界性

研究一类非线性微分系统=h(y)-φ(x),=-h(y)f(x)-g(x)k(y)解的无界性问题.给出了判断该系统解的无界性的两个新的充分条件.     

Evaluation of Certain Integrals Involving the Product of Classical Hermite's Polynomials Using Laplace Transform Technique and Hypergeometric Approach

In this paper some novel integrals associated with the product of classical Hermite's polynomials ∫_(-∞)~(+∞)(x~2)~mexp(-x~2){Hr (x)}2dx, ∫_0~∞exp(-x~2)H_(2k)(x)H_(2s+1)(x)dx,∫_0~∞exp(-x~2)H_(2k)(x)H_(2s)(x)dx and ∫_0~∞exp(-x~2)H_(2k+1)(x)H_(2s+1)(x)dx,are evaluated using hypergeometric approach and Laplace transform method, which is a different approach from the approaches given by the other authors in the field of special functions. Also the results may be of significant nature, and may yield numerous other interesting integrals involving the product of classical Hermite's polynomials by suitable simplifications of arbitrary parameters.     

关于广义Ramanujan-Nagell方程x~2+D=k~n的解数

设D、k是互素的正整数．本文运用初等方法证明了：当D是素数时，方程x2＋D＝kn至多有8组正整数解（x，n）.     

样条函数变差缩减逼近法的迭代极限

本文是[1]的进一步推广,即把[1]中所考虑的三次等距节点的样条函数推广为任意(非等距)节点与任意幂次的多项式样条函数情形.对于最一般的多项式样条函数,我们证明了它的变差缩减逼近法当其迭代次数趋于无穷时也是收敛的,并且它的极限函数由折线多边形所组成(详见本文定理3).     

一类步数为2(k+1)的次黎曼流形上测地线的研究

构造了一类步数为2(k+1)的次黎曼流形,给出其上连接原点和t轴上一点测地线的条数和相应测地线的长度,同时得到其中最短的测地线.     

A random model approach for the LASSO

The least absolute selection and shrinkage operator (LASSO) is a method of estimation for linear models similar to ridge regression. It shrinks the effect estimates, potentially shrinking some to be identically zero. The amount of shrinkage is governed by a single parameter. Using a random model formulation of the LASSO, this parameter can be specified as the ratio of dispersion parameters. These parameters are estimated using an approximation to the marginal likelihood of the observed data. The observed score equations from the approximation are biased and hence are adjusted by subtracting an empirical estimate of the expected value. After estimation, the model effects can be tested (via simulation) as the distribution of the observed data given that all model effects are zero is known. Two related simulation studies are presented that show that dispersion parameter estimation results in effect estimates that are competitive with other estimation methods (including other LASSO methods).     

影响阻尼牛顿法收敛性的两个重要参数

对阻尼牛顿算法作了适当的改进,证明了新算法的收敛性.基于新算法,运用计算机代数系统Matlab,研究了迭代次数k,参数对(μ,λ)与初值x0三者间的依赖关系,研究了病态问题在新算法下趋于稳定的渐变(瞬变)过程.数值结果表明:(1)阻尼牛顿迭代中,参数对(μ,λ)与迭代次数k间存在特有的非线性关系;(2)适当的参数对(μ,λ)与阻尼因子α的共同作用能够在迭代中大幅度地降低病态问题的Jacobi阵的条件数,使病态问题逐渐趋于稳定,从而改变原问题的收敛性与收敛速度.     

The numerical solution of a model problem biharmonic equation by using Extrapolated Alternating Direction Implicit methods

The numerical solution of the 2-dimensional biharmonic equation over the unit square by using Extrapolated Alternating Direction Implicit (E.A.D.I.) methods is studied. To approximate the biharmonic equation both a 13-point and a 25-point difference replacements are considered. In each case E.A.D.I. schemes are used together with the acceleration parameter fixed during the iterations or varying according to the Douglas set of parameters. Finally optimum E.A.D.I. schemes are given for every value of the numberN of mesh subdivisions in each co-ordinate direction.     

COMPUTATION OF THE RELAXATION OSCILLATION PERIOD IN LOTKA‐VOLTERRA SYSTEMS

ABSTRACT. This work surveys techniques of Grasman and Veling [1973], Vasil'eva and Belyanin [1988] and Shih [1996] for computing the relaxation oscillation period of singularly perturbed Lotka‐Volterra systems. Grasman and Veling [1973] used an implicit function theorem to derive an asymptotic formula for the period; Vasil'eva and Belyanin [1988] employed a method of matched asymptotic expansions to obtain an approximation to the period; Shih [1996] obtained two (exact) integral representations for the period in terms of two inverse functions W(–k, x) of xexp(x). These results are compared numerically and asymptotically. In particular, the integral representation of the period in Shih [1996] is computed numerically using a Gauss‐Tschebyscheff integration rule of the first kind, and is further investigated asymptotically by virtue of the asymptotics of W(–k, x), Laplace's method, and a method of consequent representation. Computational results indicate that the Gauss‐Tschebyscheff approximation of the period in Shih [1996] is uniformly accurate for a wide range of the singular parameter (? in the paper).     

除數問题(Ⅲ)

<正> 設d_k(n)是n分解為k個因子的數目,設 R_k(x)=(a_(k,0)+a_(k,1)ln x +…+a_(k,k-1)ln~(k-1)x)x(x>0)是ξ~k(s)x~s/s在s=1的留數.定義△_k(x)=D_k(x)-R_k(x).設σ_k真是使估計式