差分法

Finite-difference time-domain method was used to simulate the coupling processes of ultra-wide-band electromagnetic pulses into a cavity with a slot, and an anisotropic perfectly matched layer absorbing medium was inserted to truncate the computational lattices.

用时域有限差分法模拟超宽带脉冲入射时与目标腔体上的孔缝相耦合的过程，用单轴各向异性的完全匹配层吸收边界条件截断时域有限差分网格。

The technique of boundary-fitted coordinate system is used to overcome the difficulties resulting from the complicated shapes of natural river boundaries;the method of alternating direction implicit finite difference scheme is used to solve the partial differential equations in the transformed plane;and the technique of moving boundary is used to deal with the river bed exposed to water surface.

用适体坐标技术克服天然河道复杂的几何边界给有限差分法所带来的困难；用交替方向隐式有限差分格式求解变换平面上的偏微分方程；用动边界技术处理河床的淹露。

This model is a group of partial differential equations. Th solution is obtained with finite difference method to give a differential equation of gas pressure, temperature and rate and its calculation step.

该模型是一组偏微分方程，采用有限差分法对其进行求解，给出了计算气体压力、温度、速度的差分方程和详细的计算步骤。

Through the limit difference method,the partial differential equation of the semiconductor device is transformed into a difference equation,and the corresponding boundary condition is discretized with high accuracy.

采用有限差分法把器件工作的偏微分方程转化为差分方程，并将相应的边界条件转化为精度较高的离散化形式。

But for the middle and large scale problems, the computation cost by symbolic differentiation is very expensive. When the direction derivative is evaluated, the computation cost by divided difference can be reduced, but it is only one kind of approximate computation.

对于大中规模问题来说，使用符号微分，成本昂贵，有时甚至不可行，在计算导数的方向梯度时，利用差分法虽然可以降低计算成本，但得到的是近似值，而且确定恰当的差分区间也很困难。

How to calculate the synthesis operator is the key problem of controlled illumination prestack depth migration. In this paper the inverse time focusing operator is synthesized based on the traveltime calculation method of finite difference approach, and with this synthesis operator the authors calculate the focusing point controlled illumination prestack depth migration using Fourier finite difference. The test results of Marmousi model show its effectiveness and the great advantage of improving computational efficiency.

进行控制照明叠前深度偏移的关键是合成算子的选择，笔者基于有限差分的走时计算方法合成了逆时聚焦算子，基于该合成算子利用傅里叶有限差分法进行了聚焦点控制照明叠前深度偏移，针对Marmousi模型的试算结果表明了该方法的有效性及其在提高计算效率方面的巨大优势。

The method of approaching regular polygon cross section waveguide is proprosed with circle symmetry cross section waveguide.

Marcatili方法、逐点匹配方法、变分法、离散时域差分法，计算量均很大；微扰法通用性强，但规范

If the neighborhood of equation solution is solvable and meets the point- by-point Lipschitz condition, stable boundary could be obtained as the convergence of the difference method is realized, and thus the stability is ensured.

方程解的邻近如果可解并具备逐点Lipschitz条件，则差分法收敛必有稳定界存在，从而差分格式收敛性保证其稳定性，因此可以放弃线性这一重要条件。

In this paper, the maximum likelihood algorithm with process and measurement noise for nonlinear continuous-discrete system given by Jategaonkar and Plaetschke is improved in two aspects: 1 to avoid the disadvantages of sensitivities computation by common finite-difference method, in which the perturbation sizes should be selected optionally, an improved finite-difference method with best perturbations, is presented. 2 to improve the numerical stability of Jategaonkar's algorithm, maximum likelihood algorithm with fast triangular square-root decomposition filter is given.

摘要对Jategaonkar等人给出的同时计及过程及观测噪声的非线性连续-离散系统的极大似然算法从两个方面进行了改进：1给出了计算灵敏度的最佳摄动有限差分算法，避免了普通有限差分法计算灵敏度矩阵时需人为选择参数摄动量大小而带来的缺点；2给出了具有快速三角化平方根滤波的极大似然算法，提高了原算法的数值稳定性。

During the calculation of the early age temperature field, the early age physical and mechanical performance of concrete varies with its age, therefore in the second chapter we discuss the early age physical and mechanical performance of concrete and its development regulation with time, we emphasize elastic module and the development about the early age strength of concrete varying with time, at the same time consider the effect of shrink and creep upon the early age of concrete, in succession discuss how to confirm the physical parameter of thermodynamics of concrete.

之后讨论了混凝土的热物理参数的确定。为了能够正确合理的应用有限元方法求解早期混凝土温度场问题，第三章论述了求解温度场的有限元方法。第三章首先对热传导的微分方程作了阐述。之后确定温度场的边界条件。本章采用变分原理推导有限单元法计算温度场的公式。因此在第二小节叙述了变分原理，然后阐明了不稳定温度场的计算的三种方法，确定第四章分析中将采用向后差分法求解0#箱梁早期的温度场。

Cynanchum Lingtai apricot production in the average weight 65 grams, the brightly-colored fruit, juicy rich, sweet-sour taste, sweet from the nucleolus, when the late Qing Dynasty famous Shaanxi, Gansu provinces, the Qing imperial court Tongzhi tribute for years.

灵台生产的牛心杏平均单果重65克，果实色泽鲜艳，汁多味浓，甜酸适口，离核仁甜，清末时就驰名陕、甘两省，清同治年间曾为朝廷贡品。

Chenopodium album,Solanum nigrum, and Amaranthus retroflexus were very susceptible to the herbicides. Polygonum persicaria and Abutilon theophrasti were relatively less susceptible to the herbicides, and Lycopersicon esculentum was not susceptible to it. The relationship between reduction rates of weed biomass and PPM values of weed leaves 2,4, and 6 days after treatment was established.

供试的6种杂草对该混剂的敏感性存在显著差异：红心藜Chenopodium album、龙葵Solanum nigrum和反枝苋Amaranthus retroflexus对该混剂最敏感，ED90值分别为47.65、71.67和29.17g/hm2；春蓼Polygonum persicaria和苘麻Abutilon theophrasti敏感，ED90值分别为96.91、114.20g/hm2；而番茄不敏感。