[petsc-users] Galerkin multigrid coarsening

[Boris Kaus]

Hi,


While doing multigrid it is possible to explicitly set restriction and prolongation/interpolation operators in PETSC using PCMGSetRestriction and PCMGSetInterpolation.  In many cases, the restriction (R) and prolongation (P) operators are simply the transpose of each other (R=P’). 

Yet, in certain cases, for example variable viscosity Stokes with a staggered finite difference discretization, it is advantageous if they are different (see http://arxiv.org/pdf/1308.4605.pdf).

Accordding to the Wesseling textbook, Galerkin coarsening of the fine grid matrix is defined as:

Acoarse = R*A*P

Yet, as far as I can tell, PETSc seems to implement this as:

Acoarse = R*A*R’

even in the case that R is different from P’. 
Is there a way for PETSc to use the actually provided prolongation and restriction operators to compute the coarse grid approximation?

thanks!

Boris





_______________________________________________________

Boris J.P. Kaus

Institute of Geosciences, 
Geocycles Research Center &
Center for Computational Sciences.
University of Mainz, Mainz, Germany
Office: 	00-285
Tel: 		+49.6131.392.4527

http://www.geo-dynamics.eu
_______________________________________________________


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