[petsc-users] Neumann BC for interface elliptic problem

[Marco Cisternino]

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 and for the other not.
Thanks again.

     Marco