[petsc-users] GAMG and near-null-space when applying Dirichlet Conditions

[Mark Adams]

I added ", which is often the null space of the operator without boundary
conditions" to the web page doc for MatSetNearNullSpace.

On Wed, Feb 24, 2016 at 10:57 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Wed, Feb 24, 2016 at 9:45 AM, Manav Bhatia <bhatiamanav at gmail.com>
> wrote:
>
>> Hi,
>>
>>     I typically apply Dirichlet BCs by modifying the Jacobin and rhs:
>> zero constrained rows of matrix with 1.0 at diagonal, and zero
>> corresponding rows of rhs.
>>
>>     While using GAMG, is it still recommended to provide the near-null
>> space (given that the zero-eigenvalues have been removed by specification
>> of DIrichlet BCs)?
>>
>
> Yes.
>
>
>>     If that information is still needed, should the vectors be modified
>> in any manner to be consistent with the Dirichlet BCs?
>>
>
> No. You can see that if you take a small piece of the domain, apart from
> the boundary, it will have this as a null space.
>
>   Matt
>
>
>> Thanks,
>> Manav
>>
>>
>>
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
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