[petsc-users] Neumann BC for interface elliptic problem

[Barry Smith]

On Sep 13, 2011, at 10:58 AM, Marco Cisternino wrote:

> Thanks, Matthew, for the quick reply.
> My matrices are not symmetric. The differential problem is symmetric, but matrices are not.
> And not only for the presence of transmission conditions at the interface but also because I explicitly put the discretization of the forward or backward second order Neumann boundary conditions as rows in my matrix. Then even if I try to solve a problem without interfaces my matrix is not symmetric. And even in this case I got problems along the processes boundaries and about the loss of  symmetry of the solution.
> But the matrix structure is exactly the same when I solve the problem with the interface cutting the domain (always with the same implementation of Neumann boundaries conditions) with no problem.
> I can eliminate the bc rows nesting them in the discretization of the laplacian, but the interface will always give me an asymmetric matrix.
> But most of all I can't understand why for one kind of interface everything works

   What is "everything" that works? Do you mean the iterative solver converges in one case but not the other? Do you mean it always converges but the answer is wrong in one case but not the other?

    Barry

> and for the other not.
> Thanks again.
> 
>    Marco
>