[petsc-users] Is there efficeint method for matrix with one extremely small eigen value?

[Matthew Knepley]

On Wed, Apr 6, 2011 at 2:01 PM, Jed Brown <jed at 59a2.org> wrote:

> 2011/4/6 Gong Ding <gdiso at ustc.edu>
>
>> Ok, I will investigate matrix null space problem.
>> The matrix comes from nonlinear problem, I wonder if I need to calculate
>> the eigenvector each time.
>>
>
> Possibly, but it is more likely that the null space is something simple
> like a constant.
>
>
>>
>> Several months ago, some one committed DGMRES implementation, which also
>> dropped smallest eigen value.
>> It it possible to use (slightly modified) DGMRES as flexable tool for
>> sigular problem?
>>
>
> I'm not familiar with DGMRES.
>

Deflated GMRES will not help here. This is just the power method, and thus
gets the large eigenvalues
first. You will not get the null space vector.

   Matt

-- 
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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