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

[Jed Brown]

There is no boundary.
On Feb 14, 2012 5:47 PM, "Mohammad Mirzadeh" <mirzadeh at gmail.com> wrote:

> 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.
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120214/bb91e2d5/attachment.htm>