[petsc-users] Poisson problem with boundaries inside the domain

[Smith, Barry F.]

   If you using DMDA then you can't just "remove" some grid points from the vector.

   What you need to do is for your function evaluation at these interior grid points do f[j][i] = u[j][i] - ub in the FormFunction (ub is the Dirichlet value) and put a 1 one the diagonal of that row of the Jacobian (and nothing off diagonal). 

  Barry

> On Oct 30, 2017, at 10:49 AM, Mani Chandra <mc0710 at gmail.com> wrote:
> 
> Hello,
> 
> I'm trying to solve the Poisson problem but with Dirichlet boundaries inside the domain (in addition to those imposed in the ghost zones). I'm using DMDA to create a structured grid and SNES coupled to this DMDA to solve the problem. 
> 
> The issue is that SNES doesn't converge when I impose Dirichlet boundary values inside the domain. I tried setting the residual corresponding to these internal points to zero but that isn't helping. Is there a right way to approach this problem? I just want to tell SNES to remove the chosen internal grid points from the solver iterations.
> 
> Thanks,
> Mani