[petsc-users] Some questions about KSP type and PC type selection

[Matthew Knepley]

On Wed, Oct 19, 2022 at 1:04 PM Jackie Chan <chenlonglong0099 at 163.com>
wrote:

> Dear All，
>
>      I hope you're having a nice day.
>      In finite element problems, the stiffness matrix and load vector are
> constructed to calculate the displacement vector using DMCreateMatrix and
> DMCreateGlobalVector, respectively. For some reason, I need to make sure
> that the displacements of nodes on the opposite edges of two-dimensional
> structured grid domain satisfy relative displacement condition. For
> example, the displacements of two points with natural coordinates (x,Ymin)
> and (x,Ymax), i.e. the points are located on the upper and lower edges
> of 2D grid domain and have the same x-coordinates, are equal respectively.
> To achieve this, I need to add particularly big numbers to specific entries
> in stiffness matrix. In this way, the positions of big numbers are usually
> far away from each other and belong to different processes. I have tried
> many KSP types and PC settings to solve displacement vector. However, the
> final results are mostly incorrect. The best solver type I have tried is
> cg, but it still has some problems like excessive time consuming and
> convergence steps. So, for this problem, what kind of KSP type and
> PC type are suitable? Or is there a way to speed up the calculation process?
>

Do you really just want a periodic domain? It seems like you should just
make those identified nodes the same.

  Thanks,

    Matt


> Thanks,
> Jackie Chan
>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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