[petsc-users] Null space of discrete Laplace with periodic boundary conditions

[Mohammad Mirzadeh]

What do you set on the sphere? If you impose a Dirichlet  BC that makes it
nonsingular

Mohammad
On Feb 14, 2012 7:27 AM, "Jed Brown" <jedbrown at mcs.anl.gov> wrote:

> On Tue, Feb 14, 2012 at 09:20, Thomas Witkowski <
> thomas.witkowski at tu-dresden.de> wrote:
>
>> I discretize the Laplace operator (using finite element) on the unit
>> square equipped with periodic boundary conditions on all four edges. Is it
>> correct that the null space is still constant? I wounder, because when I
>> run the same code on a sphere (so a 2D surface embedded in 3D), the
>> resulting matrix is non-singular. I thought, that both cases should be
>> somehow equal with respect to the null space?
>>
>
> The continuum operators for both cases have a constant null space, so if
> either is nonsingular in your finite element code, it's a discretization
> problem.
>
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