[petsc-users] multigrid preconditioning and adaptivity

[Lukasz Kaczmarczyk]

> On 7 Mar 2016, at 12:58, Lukasz Kaczmarczyk <Lukasz.Kaczmarczyk at glasgow.ac.uk> wrote:
> 
> Hello,
> 
> I run multi-grid solver, with adaptivity, works well, however It is some space for improving efficiency. I using hierarchical approximation basis, for which 
> construction of interpolation operators is simple, it is simple injection. 
> 
> After each refinement level (increase of order of approximation on some element) I rebuild multigrid pre-conditioner with additional level. It is a way to add dynamically new levels without need of rebuilding whole MG pre-conditioner.  
> 
> Looking at execution profile I noticed that 50%-60% of time is spent on MatPtAP function during PCSetUP stage. 
> 
> Kind regards,
> Lukasz

Hello Again,

I going to have solution, such that temporally change matrix operator for MatPtAP when MG pre-conditioner is constructed, and have shell interoperation matrix P, such that in my MatPtAP, the MatGetSubMatrix is used, where needed IS for sub matrix is in the context of P matrix. In the context of P matrix I could keep as well PtAP matrix, and reused it if operation is repeated for the same level at next adaptivity step.  Is such solution is looks sound for you? Or it can be done in less complex way?

Kind regards,
Lukasz