FYI: an example of the implementation of deflated GMRES in PETSc can be found at:
http://onlinelibrary.wiley.com/doi/10.1002/nla.1882/full Possibly this helps. Kind wishes, Domenico Lahaye. ________________________________ From: Jed Brown <jedbr...@mcs.anl.gov> To: Matteo Parsani <parsani.mat...@gmail.com> Cc: Mark H. Carpenter <mark.h.carpen...@nasa.gov>; petsc-users <petsc-users@mcs.anl.gov> Sent: Monday, June 17, 2013 10:31 AM Subject: Re: [petsc-users] Deflated GMRES in PETSc [Cc'ing petsc-users since people may be interested.] Matteo Parsani <parsani.mat...@gmail.com> writes: > Hi Jed, > do you know if in PETSc we can start a Krylov iteration with problematic > eigenmodes in the Krylov subspace at the beginning of the iteration? Deflation is identical to a Galerkin coarse grid correction. I would use PCMG to create a two-level method. Write your deflation space into the prolongation operator and use Galerkin. You can compose a PCMG with other preconditioners. I would leave DGMRES to only deal with adaptive identification of those problematic modes. Note that the DGMRES basis vectors will be global, but when you provide vectors a priori, you are free to localize them. > Machinery should be there already because we see that this is used when > GMRES stagnates. > > Thanks, > > -- > Matteo
