近似导数

Based on the analysis and summary of basic ideas and methods,this thesis proposes two new estimation of error of higher order approximation.

方法二是在等距分布的条件下，基于三次样条插值函数的三弯距算法，通过利用节点处弯距的加权和近似计算区间中点处的二阶导数。

It was found that the pulse distortion can be quite severe depending on frequency, pulse width ,and path length.

应用傅立叶时域积分近似解方法对毫米脉冲波通过雨媒质时的传输特性进行了研究和分析，得出了脉冲畸变随频率、降雨率、脉冲宽度及传播距离的变化关系，讨论了脉冲展宽与压缩随传播常数二阶导数的关系。

The major implementations of the developed model include: Pseudo-spectral and finite-difference schemes are employed to approximate the spatial-differential operators in the horizontal and vertical directions, respectively. A second-order Runge-Kutta method is adopted to integrate in time for the velocity field and the free-surface elevation. The solenoidal condition of the velocity field is satisfied by solving the transformed pressure Poisson equation. A modified secant method is used to accelerate the iterative solution of the non-separable Poisson equation.

模式的主要数值方法包括：分别以拟频谱法以及二阶有限差分法近似控制方程与边界条件中的水平与垂直导数；以二阶Runge-Kutta法进行非稳态的自由液面位移与流场速度的时间积分；利用改良式割线叠代法求解计算区间中不可分离的压力Poisson方程式，以满足不可压缩流条件。

After the detailed analysis of those macro-blocks that have no forward motion estimation, the motion information is given approximatively relative to their previous reference frames.

首先根据DCT变换和MPEG编码算法，推导出子块的时空偏导数的近似计算方法，并提出了针对不同类型宏块的处理办法，然后给出了MPEG视频序列的光流场估计算法。

In the improved algorithm, the computation of three-order time derivative is replaced by convolution approximate calculation, which simplifies the computation process and reduces computation amount, and is high effective and robust.

改进算法用褶积近似运算代替时间3阶导数的求解，因此简化了计算过程，减少了计算量，是一种高效稳健的算法。

Do you know, i need you to come back

你知道吗，我需要你回来

Yang yinshu、Wang xiangsheng、Li decang,The first discovery of haemaphysalis conicinna.

1〕 杨银书，王祥生，李德昌。安徽省首次发现嗜群血蜱。