[petsc-dev] LSC question

[Barry Smith]

On Mar 9, 2012, at 12:34 PM, Jed Brown wrote:

> On Fri, Mar 9, 2012 at 11:05, Barry Smith <bsmith at mcs.anl.gov> wrote:
>    Here is the problem. We cannot use LSC with user provided L (and Lp) and PCFIELDSPLIT  now AT ALL!! That sucks, maybe we shouldn't be looking for a perfect solution but for now just one that works somewhat!
> 
> Yup, this is why I still have hacks that implement MatGetSubMatrix() to pass this stuff around. I'll follow your suggestion here. How urgent is this?

   Matt is breathing down my neck here in DC.

   Barry

>  
> 
> 
>    I will suggest the following approach. Attach various L to the original Jacobian with a different name for each. In your case L_displacement  and L_pressure, have PCFIELDSPLIT propagate them to the Schur matrix.  Then have  -prefixfromfieldsplit_pc_type lsc -prefixfromfieldplit_lsc_name L_displacement to tell LSC which one to use.
> 
>   Barry
> 
> Not perfect since the user could name the wrong lsc for the Schur index sets used but it is better than nothing.
>