共查询到20条相似文献,搜索用时 125 毫秒
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函数f(x)在区间[a,b]上单调增加(或单调减少),又c、d∈[a,b]上,若f(c)=f(a),则有c=d.1 求代数式的值例1 已知x、y∈[-π4,π4],a∈R,且 x3+sinx-2a=04y3+sinycosy+a=0则cos(x+2y)= .(1994年全国高中数学竞赛题)解 由已知条件,可得 x3+sinx=2a(-2y)3+sin(-2y)=2a故可设函数f(t)=t3+sint,则有f(x)=f(-2y)=2a.由于函数f(t)=t3+sint,在[-π2,π2]上是单… 相似文献
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二维带形无界区域中Navier—Stokes方程整体吸引子及其维数估计 总被引:5,自引:0,他引:5
该文讨论二维无界带形区域中Navier-Stokes方程(Ⅰ){ut-△u+uiэuэxi=-△p+f(x,t)∈Ω×R+(1)divu=0(2)u(X,t)∈(H^10(Ω)for t〉0(3)u(x,0)=u0(x)∈H(4)其中Ω=(0,d)×R,d〉0为一常数,u与p为未知量,其中u=(u1,u2)为速度场,p表示压力。我们证明了当u0∈H,f∈V且f「log(e+│x│^2)」^12∈L 相似文献
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在本文中,我们首先考虑了具有理系数的代数微分方程(f')n=R(z,f)亚 纯解的个数估计问题,并举例说明所得结果是精确的.其次,我们运用 Nevanlinna值 分布论,讨论了具亚纯系数的典型代数微分方程(f')3=a0(f- τ1)2(f- τ2)2(f- τ3)2 的可分解亚纯解.文中的结果推广或改进了高仕安[1],Gundersen G.和LaineI[2]以 及何育赞, LaineI.[3-5]等人的工作. 相似文献
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关于代数微分方程(f')~n=R(z,f)的亚纯解 总被引:1,自引:0,他引:1
在本文中,我们首先考虑了具有理系数的代数微分方程(f')n=R(z,f)亚 纯解的个数估计问题,并举例说明所得结果是精确的.其次,我们运用 Nevanlinna值 分布论,讨论了具亚纯系数的典型代数微分方程(f')3=a0(f- τ1)2(f- τ2)2(f- τ3)2 的可分解亚纯解.文中的结果推广或改进了高仕安[1],Gundersen G.和LaineI[2]以 及何育赞, LaineI.[3-5]等人的工作. 相似文献
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该文讨论二维无界带形区域中Navier-Stokes方程其中Ω=(0,d)×R,d>0为一常数,u与p为未知量,其中u=(u1,u2)为速度场,p表示压力.我们证明了当u0∈H,f∈V且f[log(e+|x|2)]1/2∈L2(Ω)时,问题(I)在H中存在整体吸引子A,它是的一个子集.对A的Hausdorff维数与Fractal维数我们也给出了估计. 相似文献
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曲面上离散点集的光滑插值 总被引:1,自引:0,他引:1
本文主要解决了如下问题:给定R3凸曲面上的任意个离散点{Pi}Ni=1及其对应的函数值{fi}Ni=1,要求构造曲面上的插值函数f(x),使得f(Pi)=fi,(i=1,2,…,N).本文方法推广了球面上离散点集的Multiquadric插值方法,并且对分区域插值方法也给予了讨论. 相似文献
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1 一道易错的题题目 已知f(x)=ax2-c,且-4≤f(1)≤-1,-1≤f(2)≤5,求f(3)的范围.错解 依题意得 -4≤a-c≤-1-1≤4a-c≤5①②消元可得 0≤a≤31≤c≤7③④∵ f(3)=9a-c,∴ -7≤f(3)≤26.正解 先用f(1)、f(2)表出a、c,即有 f(1)=a-cf(2)=4a-c a=13[f(2)-f(1)]c=13[f(2)-4f(1)]⑤⑥∵ f(3)=9a-c=83f(2)-53f(1),∴ 直接运用已知条件可得-1≤f(3)≤20.… 相似文献
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Theorem1 Letm∈Nandm1,P(x)beanarbitraryorderpartialdifferentialopera-tor.Thenf(x,t),φj(x)∈J.(WhereJstandforthesetofanalyticfunctioninthispaper)t+P(x)mu=f(x,t)jutjt=0=φj(x) x∈Rn,t∈R1j=0,1,2,…,m-1.u(x,t)=∫t0(t-τ)m-1(m-1)!e-(t-τ)P(x)f(x,τ)dτ+e-… 相似文献
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§1. IntroductionAtfirst,weintroduceournotations.Wedenotetheclassofallsquare-integrable2π-periodicfunctionsbyL22π,thatis,L22π={f(x)|f(x)=f(x+2π),x∈R,∫2π0|f(x)|2dx<∞}. Foranyf(x),g(x)∈L22π,theinnerproduct〈f,g〉isdefinedas〈f,g〉:=12π∫2π0f(x)g(x)dx.(1.1) … 相似文献
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Hou-de Han Chun-xiong Zheng 《计算数学(英文版)》2005,23(6):603-618
The exact boundary condition on a spherical artificial boundary is derived for thethree-dimensional exterior problem of linear elasticity in this paper. After this bound-ary condition is imposed on the artificial boundary, a reduced problem only defined in abounded domain is obtained. A series of approximate problems with increasing accuracycan be derived if one truncates the series term in the variational formulation, which isequivalent to the reduced problem. An error estimate is presented to show how the errordepends on the finite element discretization and the accuracy of the approximate problem.In the end, a numerical example is given to demonstrate the performance of the proposedmethod. 相似文献
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Hou-de Han Dong-sheng Yin 《计算数学(英文版)》2005,23(5):449-462
In this paper,the numerical solutions of heat equation on 3-D unbounded spatial do-main are considered. n artificial boundary Γ is introduced to finite the computationaldomain.On the artificial boundary Γ,the exact boundary condition and a series of approx-imating boundary conditions are derived,which are called artificial boundary conditions.By the exact or approximating boundary condition on the artificial boundary,the originalproblem is reduced to an initial-boundary value problem on the bounded computationaldomain,which is equivalent or approximating to the original problem.The finite differencemethod and finite element method are used to solve the reduced problems on the finitecomputational domain.The numerical results demonstrate that the method given in thispaper is effective and feasible. 相似文献
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Summary. In this paper we consider the numerical simulations of the incompressible materials on an unbounded domain in . A series of artificial boundary conditions at a circular artificial boundary for solving incompressible materials on an
unbounded domain is given. Then the original problem is reduced to a problem on a bounded domain, which be solved numerically
by a mixed finite element method. The numerical example shows that our artificial boundary conditions are very effective.
ReceivedJune 7, 1995 / Revised version received August 19, 1996 相似文献
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Weizhu Bao & Houde Han 《计算数学(英文版)》1997,15(4):335-344
1.IntroductionManyboundaxyvaJueproblemsofpartialdiffereotialequationsinvo1vingunboundeddomainoccurinmanyareasofapplications,e-g.lfluidflowaroundobstacles,couplingofstructureswithfoundationandsoon.Forgettingthenumericalsolutionsoftheproblemsonunboundeddomian,anaturalapproachistocutoffanunboundedpartofthedomainbyintroducinganartificialboundaryandsetupanaPpropriatear-tificialboundaryconditiononthearti%ialboundaryThentheoriginalproblemisapproximatedbyaproblemonbou.d.dfdomain.Inthelastteny6aJrs,b… 相似文献
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Oliver G. Ernst 《Numerische Mathematik》1996,75(2):175-204
Summary. We introduce an algorithm for the efficient numerical solution of exterior boundary value problems for the Helmholtz equation.
The problem is reformulated as an equivalent one on a bounded domain using an exact non-local boundary condition on a circular
artificial boundary. An FFT-based fast Helmholtz solver is then derived for a finite-element discretization on an annular
domain. The exterior problem for domains of general shape are treated using an imbedding or capacitance matrix method. The
imbedding is achieved in such a way that the resulting capacitance matrix has a favorable spectral distribution leading to
mesh independent convergence rates when Krylov subspace methods are used to solve the capacitance matrix equation.
Received May 2, 1995 相似文献
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In this paper, we present a general ellipsoidal artificial boundary method for three-dimensional exterior problem. The exact artificial boundary condition, which is expressed explicitly by the series concerning the ellipsoidal harmonic functions, is derived and then an equivalent problem in a bounded domain is presented. The error estimates show that the convergence rate depends on the mesh parameter, the number of terms used in the exact artificial boundary condition, and the location of the artificial boundary. 相似文献
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A sensitive issue in numerical calculations for exterior flow problems, e.g.around airfoils, is the treatment of the far field boundary conditions on a computational domain which is bounded. In this paper we investigate this problem for two-dimensional transonic potential flows with subsonic far field flow around airfoil profiles. We take the artificial far field boundary in the subsonic flow region. In the far field we approximate the subsonic potential flow by the Prandtl-Glauert linearization. The latter leads via the Green representation theorem to a boundary integral equation on the far field boundary. This defines a nonlocal boundary condition for the interior ring domain. Our approach leads naturally to a coupled finite element/boundary element method for numerical calculations. It is compared with local boundary conditions. The error analysis for the method is given and we prove convergence provided the solution to the analytic transonic flow problem around the profile exists.
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The exterior boundary value problems of Laplace equation and linear elastic equations are considered. A series of approximate infinite boundary conditions are given. Then the original problem is reduced to a boundary value problem on a bounded domain. The finite element approximation of this problem and its error estimate are obtained. Finally, a numerical example shows that this method is very effective. 相似文献
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Hou-De Han & Wei-Zhu Bao 《计算数学(英文版)》1995,13(1):51-63
1.IntroductionWhencomputingthenumericals0luti0nsofviscousfluidfl0wproblemsinallun-boundedd0main,0neoftenintroducesartificialboundaries,andsetsupanartificialbopundarycondition0nthem;thenthe0riginalproblemisreducedtoaproblemonab0undedc0mputationald0main.InordertoIimitthecomputatio11alcost,theseboundariesmustnotbet00farfromthedomainofinterest.Theref0re,theartificialboundaryc0nditi0nsmustbegoodapprotimationt0the"exact"boundaryconditions(sothatthes0lutionoftheproblemintheboundeddonlainisequaltothes… 相似文献