Comments (4)
Provide your .md
source file, I will try to optimize in VLOOK V9.2
.
Thanks for your support!
from vlook.
Here is the source .md file. Thank you!
---
title: 工作日志
---
# BDF1和BDF2的BLUSGS实现
对于微分方程
$$
\frac{\partial Q}{\partial t} = R(Q)
$$
BDF1和BDF2的理论公式如下
$$
\begin{align}
Q^{n+1} - Q^{n} &= \Delta t R^{n+1} \\
Q^{n+1} - \frac{4}{3} Q^{n} + \frac{1}{3} Q^{n-1} &= \frac{2}{3} \Delta t R^{n+1} \\
\end{align}
$$
## BDF1的BLUSGS实现
BLUSGS算法描述见:Sun, Y.; Wang, Z. & Liu, Y. Efficient Implicit Non-linear LU-SGS Approach for Compressible Flow Computation Using High-order Spectral Difference Method, *Comm. Comput. Phys.,* **2009***, 5*, 760-778
- BDF1的原始形式
$$
\begin{align}
\frac{ Q^{n+1} - Q^{n} }{\Delta t} &= R^{n+1} \\
\frac{ Q^{n+1} - Q^{n} }{\Delta t} - \left ( R^{n+1} - R^{n} \right ) &= R^{n} \\
\end{align}
$$
- 线化$R^{n+1}-R^{n}$
$$
\begin{align}
R^{n+1} - R^{n} = \frac{\partial R_c}{\partial Q_c} \Delta Q^{n+1}_c + \sum \frac{\partial R_{c}}{\partial Q_{nb}} \Delta Q^{n+1}_{nb}
\end{align}
$$
- 将线化$R$代入原始形式
$$
\begin{align}
\Delta Q^{n+1} &= Q^{n+1} - Q^{n} \\
\frac{ \Delta Q^{n+1} }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \Delta Q^{n+1}_c - \sum \frac{\partial R_{c}}{\partial Q_{nb}} \Delta Q^{n+1}_{nb} &= R^n_c \\
\left ( \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \Delta Q^{n+1}_c - \sum \frac{\partial R_{c}}{\partial Q_{nb}} \Delta Q^{n+1}_{nb} &= R^n_c \\
\end{align}
$$
- Gauss-Seidel加速
$$
\begin{align}
\left ( \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \Delta Q^{k+1}_c - \sum \frac{\partial R_{c}}{\partial Q_{nb}} \Delta Q^{k}_{nb} &= R^n_c \\
\Delta Q^{k+1}_c &= Q^{k+1} - Q^{n} \\
\end{align}
$$
- 再次线化$R^{k}-R^{n}$
$$
R^{k} - R^{n} = \frac{\partial R_c}{\partial Q_c} \Delta Q^{k}_c + \sum \frac{\partial R_{c}}{\partial Q_{nb}} \Delta Q^{k}_{nb}
$$
- 将线化$R$代入,整理
$$
\begin{align}
\left ( \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \Delta Q^{k+1}_c &= R^k_c - \frac{\partial R_{c}}{\partial Q_{c}} \Delta Q^{k}_{c} \\
&= R^k_c + \left ( \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \Delta Q^{k}_{c} - \frac{ I }{\Delta t} \Delta Q^{k}_{c} \\
\left ( \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \left ( \Delta Q^{k+1}_c - \Delta Q^{k}_{c} \right ) &= R^k_c - \frac{ I }{\Delta t} \Delta Q^{k}_{c} \\
\left ( \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \tilde{\Delta} Q^{k+1}_c &= R^k_c - \frac{ I }{\Delta t} \Delta Q^{k}_{c} \\
\tilde{\Delta} Q^{k+1}_c &= Q^{k+1}_c - Q^{k}_c \\
\end{align}
$$
最后两个方程是最终的BDF1的BLUSGS实现。
## BDF2的BLUSGS实现
BDF2的实现与BDF1类似。
- BDF2的原始形式
$$
\begin{align}
\frac{ Q^{n+1} - \frac{4}{3} Q^{n} + \frac{1}{3} Q^{n-1} }{ \frac{2}{3} \Delta t } &= R^{n+1} \\
\frac{3}{2} \left ( \frac{ \Delta Q^{n+1} }{ \Delta t } - \frac{1}{3} \frac{ \Delta Q^{n} }{ \Delta t } \right ) - \left ( R^{n+1} - R^{n} \right ) &= R^{n} \\
\Delta Q^{n+1} &= Q^{n+1} - Q^{n} \\
\end{align}
$$
- 线化$R^{n+1}-R^{n}$
$$
\begin{align}
R^{n+1} - R^{n} = \frac{\partial R_c}{\partial Q_c} \Delta Q^{n+1}_c + \sum \frac{\partial R_{c}}{\partial Q_{nb}} \Delta Q^{n+1}_{nb}
\end{align}
$$
- 将线化$R$代入原始形式
$$
\begin{align}
\left ( \frac{3}{2} \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \Delta Q^{n+1}_c - \frac{1}{2} \frac{ I }{\Delta t} \Delta Q^{n}_c - \sum \frac{\partial R_{c}}{\partial Q_{nb}} \Delta Q^{n+1}_{nb} &= R^n_c \\
\end{align}
$$
- Gauss-Seidel加速
$$
\begin{align}
\left ( \frac{3}{2} \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \Delta Q^{k+1}_c - \frac{1}{2} \frac{ I }{\Delta t} \Delta Q^{n}_c - \sum \frac{\partial R_{c}}{\partial Q_{nb}} \Delta Q^{k}_{nb} &= R^n_c \\
\Delta Q^{k+1}_c &= Q^{k+1} - Q^{n} \\
\end{align}
$$
- 再次线化$R^{k}-R^{n}$
$$
R^{k} - R^{n} = \frac{\partial R_c}{\partial Q_c} \Delta Q^{k}_c + \sum \frac{\partial R_{c}}{\partial Q_{nb}} \Delta Q^{k}_{nb}
$$
- 将线化$R$代入,整理
$$
\begin{align}
\left ( \frac{3}{2} \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \Delta Q^{k+1}_c - \frac{1}{2} \frac{ I }{\Delta t} \Delta Q^{n}_c &= R^k_c - \frac{\partial R_{c}}{\partial Q_{c}} \Delta Q^{k}_{c} \\
&= R^k_c + \left ( \frac{3}{2} \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \Delta Q^{k}_{c} - \frac{3}{2} \frac{ I }{\Delta t} \Delta Q^{k}_{c} \\
\left ( \frac{3}{2} \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \left ( \Delta Q^{k+1}_c - \Delta Q^{k}_{c} \right ) - \frac{1}{2} \frac{ I }{\Delta t} \Delta Q^{n}_c &= R^k_c - \frac{3}{2} \frac{ I }{\Delta t} \Delta Q^{k}_{c} \\
\left ( \frac{3}{2} \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \tilde{\Delta} Q^{k+1}_c &= R^k_c - \frac{3}{2} \frac{ I }{\Delta t} \Delta Q^{k}_{c} + \frac{1}{2} \frac{ I }{\Delta t} \Delta Q^{n}_c \\
\left ( \frac{3}{2} \frac{ I }{\Delta t} - \frac{\partial R_c}{\partial Q_c} \right ) \tilde{\Delta} Q^{k+1}_c &= R^k_c - \frac{1}{2 \Delta t} \left ( 3 I Q^{k}_{c} - 4 I Q^{n}_c + I Q^{n-1}_c \right ) \\
\tilde{\Delta} Q^{k+1}_c &= Q^{k+1}_c - Q^{k}_c \\
\end{align}
$$
最后两个方程是最终的BDF2的BLUSGS实现。
from vlook.
The problem you said will be fixed in Version 9.2. Should be released in the next two weeks.
from vlook.
The problem you said will be fixed in Version 9.2. Should be released in the next two weeks.
Thank you!
from vlook.
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