用等价无穷小代换求极限的两个误区

普遍认为利用等价无穷小代换求代数和及复合函数的极限时常常隐藏着两个误区,通过对其进行探讨可以发现．只要加以适当的条件,代数和各部分为无穷小量以及复合函数的中间变量为无穷小量时．对这些部分是可以进行等价无穷小代换的．     

用等价无穷小代换求极限中的一些问题

学生用等价无穷小代换求极限的过程中出现许多我们认为是错误的方法，但有些错误的方法又能够得到正确的结论，如求极限时对复合函数的中间变量作等价无穷小代换；两非等价无穷小和差分别做等价无穷小代换等，这应该算对还是错？本文在理论上作了分析．     

泰勒公式在含三层复合函数的不定式极限计算中的应用

本文探讨了一个含三层复合函数(由两层幂指函数复合而得的)的0/0型不定式极限,除了L′Hospital法则、等价无穷小替换、带Peano余项的泰勒公式等经典方法外,还需结合使用一阶带Lagrange余项的泰勒公式进行求解.     

利用函数中间变量等价无穷小代换求极限

研究了一类极限,极限中函数的中间变量是无穷小,但函数本身并不是无穷小,利用中间变量等价无穷小的代换得到了极限的简化计算方法.     

一组未定型的定值命题

<正> 未定型(不定式)的定值问题,是极限计算中的一个重要问题。学生在未掌握罗必塔法则之前,对如何解决未定型定值问题,往往感到较困难,教师如能在教学中引导学生综合运用两个重要极限、等价无穷小代换及复合函数极限定理等来解决未定型定值问题,不仅可以     

差函数的等价无穷小代换

分析了差函数等价无穷小代换求极限应该注意的问题及差函数常用的等价无穷小。     

巧用等价无穷小代换

<正> 未定型(不定式)的定值问题,是极限计算中的一个重要问题.在未掌握罗必塔法则之前,对如何解决未定型定值问题,往往感到困难,如能综合运用两个重要极限、等价无穷小代换及复合函数极限定理等来解决未定型定值问题,不仅可以巩固已学的知识,克服存在的困难,而且还可以提高综合运用所学知识分析问题和解决问题的能力.     

用等价无穷小替换求极限的几点注释

在这篇文章里讨论了几个函数和与差的等价无穷小问题,对高等数学教材中利用等价无穷小替换求极限的适用范围进行了拓广,并得到了可用等价无穷小替换求极限的新的充要条件.     

无须极限新微分法

本文摆脱传统的除法 ,以括代除 ,无须极限也能求出切线 ,作出定理 A.由此微积分完全改观 .这是依靠实数有序“无漏”,建立强无穷小ω(Δx) ,取代ε-δ,实质又相互等价 ,作出定理 B.由ω(Δx)定义无穷小与连续 ,由连续再作极限更为自然 .聚点是极限的初步 ,大可发挥 .     

求0~0型极限在弱条件下的简便方法

利用洛必达法则与等价无穷小代换对抽象函数的00型极限可得结论:设当x→x0时f(x)与g(x)为无穷小,g(x)～(x-x0)β,取k为正实数,使得fk(x)=A(x-x0)α+o[(x-x0)α],其中A0,α≥2,β0为实数,则有limx→x0f(x)g(x)=1.该方法对求常见的00型极限都适用.当使用洛必达法则求li mx→x0f(x)g(x)很复杂时,使用该方法可简化计算.     

Evaluating the exact infinitesimal values of area of Sierpinski’s carpet and volume of Menger’s sponge

Very often traditional approaches studying dynamics of self-similarity processes are not able to give their quantitative characteristics at infinity and, as a consequence, use limits to overcome this difficulty. For example, it is well known that the limit area of Sierpinski’s carpet and volume of Menger’s sponge are equal to zero. It is shown in this paper that recently introduced infinite and infinitesimal numbers allow us to use exact expressions instead of limits and to calculate exact infinitesimal values of areas and volumes at various points at infinity even if the chosen moment of the observation is infinitely faraway on the time axis from the starting point. It is interesting that traditional results that can be obtained without the usage of infinite and infinitesimal numbers can be produced just as finite approximations of the new ones. The importance of the possibility to have this kind of quantitative characteristics for E-Infinity theory is emphasized.     

Infinitesimal variations of Hodge structure at infinity

By analyzing the local and infinitesimal behavior of degenerating polarized variations of Hodge structure the notion of infinitesimal variation of Hodge structure at infinity is introduced. It is shown that all such structures can be integrated to polarized variations of Hodge structure and that, conversely, all are limits of infinitesimal variations of Hodge structure at finite points. As an illustration of the rich information encoded in this new structure, some instances of the maximal dimension problem for this type of infinitesimal variation are presented and contrasted with the “classical” case of IVHS at finite points.      

Matrix technique for nonperturbative Green function of time-independent Schrödinger equation

A Green function of time-independent multi-channel Schrödinger equation is considered in matrix representation beyond a perturbation theory. Nonperturbative Green functions are obtained through the regular in zero and at infinity solutions of the multi-channel Schrödinger equation for different cases of symmetry of the full Hamiltonian. The spectral expansions for the nonperturbative Green functions are obtained in simple form through multi-channel wave functions. The developed approach is applied to obtain simple analytic equations for the Green functions and transition matrix elements for compound multi-potential system within quasi-classical approximation. The limits of strong and weak inter-channel interactions are studied.     

Integral Representations,Differentiability Properties and Limits at Infinity for Beppo Levi Functions

The first aim in the present paper is to give an integral representation for Beppo Levi functions on R ⁿ. Our integral representation is an extension of Sobolev's integral representation given for infinitely differentiable functions with compact support. As applications, continuity and differentiability properties of Beppo Levi functions are studied.Our second aim in this paper is to study the existence of limits at infinity for Beppo Levi functions. We also consider the existence of fine-type limits at infinity with respect to Bessel capacities, which yields the radial limit result at infinity.     

On Semi-fine Limits at Infinity for Riesz Potentials and Monotone BLD Functions

Semi-fine limits at infinity are studied for Riesz potentials of functions on R ⁿ with a certain growth condition. We are also concerned with monotone BLD functions.     

对教材中0~0型极限内容的建议

"00型是一种结果不确定的类型,并且可以使用洛必达法则来转化解决"是高等数学大纲要求中的一个重点.现行"高等数学"教材和参考书中都指出了这一点,但给出的有关00型极限的例子和习题的结果都为1.这严重影响了教学效果和教学目的.通过实例可对该内容的教学和教材组织提供一种富有建设性的建议.     

ON COHOMOLOGY OF INFINITESIMAL NEIGHBOURHOODS OF COMPLEX MANIFOLDS

In this paper,we introduce the concept of the(k,l)-th C~∞ infinitesimal neighbour-hoods of complex manifold M and difine defferential modules _(M,k-p,l-q)~(p,q) and _(M,k,l)~r forthe(k,l)-th C~∞ infinitesimal neighbourhoods.We prove some isomorphism theorems ofcohomology and hyper cohomology concerning _(M,k-p)~p and _(M,k-p)~,as followsH~p(M,_(M,k-r)~r)≈H_~p(M,_(M,k-r,l-*)~(r,*),H~p(M,_(M,k,l)~*)≈H_(DR)~p(M,C)and for hyper cohomologyH~p(M,_(M,k-*)~*≈H~p(M,C),H~p(M,_(M,k-*)~*)≈H~p(M,O_M).