[petsc-users] Saddle point problem with nested matrix and a relatively small number of Lagrange multipliers

[Olivier Jamond]

Thanks for your answer, whereas being 'sad' to me! Do you have any idea 
how the structure FE code geared toward HPC deals with their Lagrange 
multipliers for their BCs? Do they 'accept' that cost?

To my understanding, I didn't know the Sherman-Morrison formula, and I 
am not sure to see how it applies to my case... Could you please help me 
on that?

Many thanks,
Olivier

>
> I am not sure you can get around this cost. In this case, it reduces 
> to the well-known
> Sherman-Morrison formula 
> (https://en.wikipedia.org/wiki/Sherman%E2%80%93Morrison_formula),
> which Woodbury generalized. It seems to have the same number of solves.
>
>
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