how to output quantities involving time derivatives in pdepe

2 次查看（过去 30 天）
feynman feynman
feynman feynman 2024-2-13
评论： Torsten 2024-2-13
pdeval only seems to output the solution and the spatial derivative of the solution via [~,dudx]=pdeval(m,x,sol(i,:,1),x). It seems it's no use putting dudt in as in [~,dudt]=pdeval(m,x,sol(i,:,1),x). How to output quantities involving time derivatives of the solution and the like?

请先登录，再回答此问题。

采纳的回答

Torsten
Torsten 2024-2-13
编辑：Torsten 2024-2-13
You don't have access to the spatial discretization of pdepe, thus no access to the exact time derivatives. But if you choose the output vector t fine enough, you can use the usual finite difference quotient in time:
dersol_t(i,:) = (sol(i+1,:,1)-sol(i,:,1))/(t(i+1)-t(i))
Maybe "deval" also works - I'm not sure. You can test it.
https://uk.mathworks.com/help/matlab/ref/deval.html
  2 个评论
feynman feynman
feynman feynman 2024-2-13
编辑：feynman feynman 2024-2-13
thanks! dersol_t(i,:) = (sol(i+1,:,1)-sol(i,:,1))/(t(i+1)-t(i)) is what I thought of but I wish there were sth provided by matlab that is more accurate.
I have no idea how to make deval work for pdepe solutions since deval(~,sol,~) requires sol to be an ode solution struct out of ode23,45 etc. Maybe I can forge an ode struct by hand?
Torsten
Torsten 2024-2-13
You can attain higher order accuracy if you use more accurate difference formulae than the simple Euler forward I suggested. I think "deval" can't do better - at least if the ode integrator with which the results were achieved is not known to "deval" by the sol structure.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Ordinary Differential Equations 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by