If you can use petsc-dev, there is a feature branch (karpeev/ksp-matschurcomplement) that allows to assemble the Schur complement used by PCFIELDSPLIT. While ordinarily this is a bad idea, since it requires inversion of the A00-block and results in a dense matrix, it can be done very cheaply, if your A00-block is diagonal. That is indeed the case when the 0-split consists of the Dirichlet-constrained degrees of freedom. Then the Schur complement will be the condensed matrix you want and will be of the same type as your A11 block. You can then use PCFIELDSPLIT recursively on it, if desired. This functionality should be in the next petsc release.
Dmitry. On Mon, Jan 27, 2014 at 3:02 PM, James MBewu <[email protected]> wrote: > Hi All, > > Probably a silly question, but is it possible to condense out the rows and > columns corresponding to dirichlet boundary conditions so that the > resulting system matrix to solve is smaller (using lagrange type elements). > I'm using a DirichletBoundary object to apply homogenous constraints to a > large number of nodes on the walls of a cylinder and then solving using > Petsc, but it doesn't seem to condense out the rows and columns. Is this > because it is bad for Petsc and sparsity structure and things (I am using > fieldsplit so I guess the arrangement of unknowns is possibly important to > Petsc and/or preconditioners)? Would it be easy/useful to implement this > myself? Oh yes and I'm solving Navier Stokes with Q2-Q1 elements. > > Thanks, > James > > ------------------------------------------------------------------------------ > CenturyLink Cloud: The Leader in Enterprise Cloud Services. > Learn Why More Businesses Are Choosing CenturyLink Cloud For > Critical Workloads, Development Environments & Everything In Between. > Get a Quote or Start a Free Trial Today. > > http://pubads.g.doubleclick.net/gampad/clk?id=119420431&iu=/4140/ostg.clktrk > _______________________________________________ > Libmesh-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/libmesh-users > ------------------------------------------------------------------------------ CenturyLink Cloud: The Leader in Enterprise Cloud Services. Learn Why More Businesses Are Choosing CenturyLink Cloud For Critical Workloads, Development Environments & Everything In Between. Get a Quote or Start a Free Trial Today. http://pubads.g.doubleclick.net/gampad/clk?id=119420431&iu=/4140/ostg.clktrk _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
