后向差商

Douglas and Russell first presented the idea of characteristics in[13],in whichthe diffusion term is included in the derivative of characteristic direction of the solu-tion and the backward difference quotient along the time axis was replaced by it alongcharacteristic direction.

Douglas，Russell[13]最先提出了特征法的思想，其主要特点是将模型方程的对流项隐含在解沿特征方向的导数之中，以沿特征方向的向后差商逼近取代通常方法中沿时间方向的向后差商逼近。

Because the diffusive term is discretized with divided forward difference or divided backward difference according to the sign of convection velocity, these methods keep first order accuracy for diffusive term.

3.2考虑规则网格上的一维和二维定常型对流占优扩散问题，离散方法采用了有限体积方法及普通的有限差分方法，基本离散思想是将对流项提高到二阶精度，扩散项则根据对流速度的方向决定采用向前或向后差商离散。

In the United States, chronic alcoholism and hepatitis C are the most common ones.

在美国，慢性酒精中毒，肝炎是最常见的。

If you have any questions, you can contact me anytime.

如果有任何问题，你可以随时联系我。