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1.
On some inequalities for the gamma and psi functions   总被引:12,自引:0,他引:12  
We present new inequalities for the gamma and psi functions, and we provide new classes of completely monotonic, star-shaped, and super-additive functions which are related to and .

  相似文献

2.
任意流场中稀疏颗粒运动方程及其性质   总被引:10,自引:0,他引:10  
通过研究和比较稀疏刚性颗凿相对流体运动时所受到的各种人艇力,并考虑在不同流动条件下各作用修正问题从而得到了任意流场中稀疏颗粒运动方程的一般形式,然后分析了该方程的数学性质,采用积分变换方法对该方程的基本形式进行了理论解析,最后探讨了闰物理性质对其运动规律的影响,以及几种典型流场中稀疏颗粒的运动特性,得到了一些有意义的结论  相似文献
3.
有限区间上的分数阶扩散-波方程定解问题与Laplace变换   总被引:6,自引:0,他引:6  
求解了如下的分数阶扩散-波方程定解问题0Dαtu=2ux2,00,0<α≤2,u(0,t;α)=0,u(1,t;α)=θ(t),u(x,0+;α)=0,当1<α≤2时,还有ut(x,0+;α)=0.其中θ(t)是Heaviside单位阶跃函数,0Dαt为关于时间t的α阶Caputo分数阶导数算子,u=u(x,t;α)为时间t的因果函数(即t<0时恒为零的函数).利用Laplace变换的复围道积分反演和离散化反演及FoxH函数理论,给出在计算上对大的t和小的t分别适用的解的表达式.  相似文献
4.
This paper reviews the Fourier-series method for calculating cumulative distribution functions (cdf's) and probability mass functions (pmf's) by numerically inverting characteristic functions, Laplace transforms and generating functions. Some variants of the Fourier-series method are remarkably easy to use, requiring programs of less than fifty lines. The Fourier-series method can be interpreted as numerically integrating a standard inversion integral by means of the trapezoidal rule. The same formula is obtained by using the Fourier series of an associated periodic function constructed by aliasing; this explains the name of the method. This Fourier analysis applies to the inversion problem because the Fourier coefficients are just values of the transform. The mathematical centerpiece of the Fourier-series method is the Poisson summation formula, which identifies the discretization error associated with the trapezoidal rule and thus helps bound it. The greatest difficulty is approximately calculating the infinite series obtained from the inversion integral. Within this framework, lattice cdf's can be calculated from generating functions by finite sums without truncation. For other cdf's, an appropriate truncation of the infinite series can be determined from the transform based on estimates or bounds. For Laplace transforms, the numerical integration can be made to produce a nearly alternating series, so that the convergence can be accelerated by techniques such as Euler summation. Alternatively, the cdf can be perturbed slightly by convolution smoothing or windowing to produce a truncation error bound independent of the original cdf. Although error bounds can be determined, an effective approach is to use two different methods without elaborate error analysis. For this purpose, we also describe two methods for inverting Laplace transforms based on the Post-Widder inversion formula. The overall procedure is illustrated by several queueing examples.  相似文献
5.
We consider the discretization in time of an inhomogeneous parabolicequation in a Banach space setting, using a representation ofthe solution as an integral along a smooth curve in the complexleft half-plane which, after transformation to a finite interval,is then evaluated to high accuracy by a quadrature rule. Thisreduces the problem to a finite set of elliptic equations withcomplex coefficients, which may be solved in parallel. The paperis a further development of earlier work by the authors, wherewe treated the homogeneous equation in a Hilbert space framework.Special attention is given here to the treatment of the forcingterm. The method is combined with finite-element discretizationin spatial variables.  相似文献
6.
时间分数阶扩散-反应方程   总被引:5,自引:0,他引:5  
1、引言 当前,对含有非整数阶导数和积分的方程的研究正引起越来越多学者的关注,这类分数阶导数和积分将广泛应用于科学和工程的各个领域.  相似文献
7.
Time discretization of an evolution equation via Laplace transforms   总被引:4,自引:0,他引:4  
Following earlier work by Sheen, Sloan, and Thomée concerningparabolic equations we study the discretization in time of aVolterra type integro-differential equation in which the integraloperator is a convolution of a weakly singular function andan elliptic differential operator in space. The time discretizationis accomplished by using a modified Laplace transform in timeto represent the solution as an integral along a smooth curveextending into the left half of the complex plane, which isthen evaluated by quadrature. This reduces the problem to afinite set of elliptic equations with complex coefficients,which may be solved in parallel. Stability and error boundsof high order are derived for two different choices of the quadraturerule. The method is combined with finite-element discretizationin the spatial variables.  相似文献
8.
基于直接数值积分的Laplace逆变换方法的比较研究   总被引:3,自引:0,他引:3  
为了探讨各种数值积分方法,如梯形公式、Simpson法、Gauss积分方法和振荡函数积分方法等,在数值Laplace逆变换中的应用效果,本文进行了基于各种离散数值积分公式的Laplace逆变换方法的比较研究,涉及到24种方法,针对Davies和Martin的16个考题,给出了数值比较结果,得出了一些新的结论。  相似文献
9.
相应于随机自相似分形的记忆函数和分数次积分   总被引:2,自引:0,他引:2  
梁洪亮  刘孝书 《数学季刊》2003,18(2):186-191
For a physics system which exhibits memory, if memory is preserved only at points of random self-similar fractals, we define random memory functions and give the connection between the expectation of flux and the fractional integral. In particular, when memory sets degenerate to Cantor type fractals or non-random self-similar fractals our results coincide with that of Nigmatullin and Ren et al. .  相似文献
10.
预解算子族的一个推广   总被引:2,自引:0,他引:2  
本文引入了正则预解族的概念,给出了其若干性质及两个特征,所得结果推广了预解算子族的相应结果.  相似文献
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