Thanks Barry. I will look into DMMGSetKSP and your suggestions. Shao-Ching
On Tue, Sep 28, 2010 at 7:13 PM, Barry Smith <bsmith at mcs.anl.gov> wrote: > > ?If you are using DMMGSetKSP() then just have the third argument (func) > compute A+B as the first matrix and A as the second matrix. Then the > smoothing and coarse grid solve will > only use the A entries. That is A+B will be preconditioned with geometric > multigrid applied to A. > > ? But, I suspect that you will do just as well using A+B. > > ? Barry > > On Sep 28, 2010, at 8:19 PM, Shao-Ching Huang wrote: > >> Hi >> >> I can trying to solve a linear system >> >> (A+B)x=b >> >> where A is the standard finite difference Laplacian matrix and B has >> only a few elements (i.e. B's number of non-zero entries is much much >> smaller than A's). >> Is it possible to precondition by applying DMMG on A (like in ex34.c) >> in a KSP solver? Is there an example that I can follow to set this up? >> >> Thanks, >> >> Shao-Ching > >
