Hi, Lisandro I have tried to use BoomerAMG for my problem. My problem is a set of elliptic-type linear PDEs. They are strong coupled. The convergence was bad. I tried to adjust some parameters, the convergence had some improvements and was always bad. I have little knowledge about your problem. I have discussed my problem with Hypre developers, they told me that if the PDEs are strong coupled, it is difficult to use BoomerAMG.
Regards, Yujie On 2/5/08, Lisandro Dalcin <dalcinl at gmail.com> wrote: > > Ben, some time ago I was doing some testing with PETSc for solving > incompressible NS eqs with fractional step method. I've found that in > our software and hardware setup, the best way to solve the pressure > problem was by using HYPRE BoomerAMG. This preconditioner usually have > some heavy setup, but if your Poison matrix does not change, then the > sucessive solves at each time step are really fast. > > If you still want to use a direct method, you should use the > combination '-ksp_type preonly -pc_type lu' (by default, this will > only work on sequential mode, unless you build PETSc with an external > package like MUMPS). This way, PETSc computes the LU factorization > only once, and at each time step, the call to KSPSolve end-up only > doing the triangular solvers. > > The nice thing about PETSc is that, if you next realize the > factorization take a long time (as it usually take in big problems), > you can switch BoomerAMG by only passing in the command line > '-ksp_type cg -pc_type hypre -pc_hypre_type boomeramg'. And that's > all, you do not need to change your code. And more, depending on your > problem you can choose the direct solvers or algebraic multigrid as > you want, by simply pass the appropriate combination options in the > command line (or a options file, using the -options_file option). > > Please, if you ever try HYPRE BoomerAMG preconditioners, I would like > to know about your experience. > > Regards, > > On 2/5/08, Ben Tay <zonexo at gmail.com> wrote: > > Hi everyone, > > > > I was reading about the topic abt inversing a sparse matrix. I have to > > solve a poisson eqn for my CFD code. Usually, I form a system of linear > > eqns and solve Ax=b. The "A" is always the same and only the "b" changes > > every timestep. Does it mean that if I'm able to get the inverse matrix > > A^(-1), in order to get x at every timestep, I only need to do a simple > > matrix multiplication ie x=A^(-1)*b ? > > > > Hi Timothy, if the above is true, can you email me your Fortran code > > template? I'm also programming in fortran 90. Thank you very much > > > > Regards. > > > > Timothy Stitt wrote: > > > Yes Yujie, I was able to put together a parallel code to invert a > > > large sparse matrix with the help of the PETSc developers. If you need > > > any help or maybe a Fortran code template just let me know. > > > > > > Best, > > > > > > Tim. > > > > > > Waad Subber wrote: > > >> Hi > > >> There was a discussion between Tim Stitt and petsc developers about > > >> matrix inversion, and it was really helpful. That was in last Nov. > > >> You can check the emails archive > > >> > > >> > http://www-unix.mcs.anl.gov/web-mail-archive/lists/petsc-users/2007/11/threads.html > > >> > > >> > > >> Waad > > >> > > >> */Yujie <recrusader at gmail.com>/* wrote: > > >> > > >> what is the difference between sequantial and parallel AIJ > matrix? > > >> Assuming there is a matrix A, if > > >> I partitaion this matrix into A1, A2, Ai... An. > > >> A is a parallel AIJ matrix at the whole view, Ai > > >> is a sequential AIJ matrix? I want to operate Ai at each node. > > >> In addition, whether is it possible to get general inverse using > > >> MatMatSolve() if the matrix is not square? Thanks a lot. > > >> > > >> Regards, > > >> Yujie > > >> > > >> > > >> On 2/4/08, *Barry Smith* <bsmith at mcs.anl.gov > > >> <mailto:bsmith at mcs.anl.gov>> wrote: > > >> > > >> > > >> For sequential AIJ matrices you can fill the B matrix > > >> with the > > >> identity and then use > > >> MatMatSolve(). > > >> > > >> Note since the inverse of a sparse matrix is dense the B > > >> matrix is > > >> a SeqDense matrix. > > >> > > >> Barry > > >> > > >> On Feb 4, 2008, at 12:37 AM, Yujie wrote: > > >> > > >> > Hi, > > >> > Now, I want to inverse a sparse matrix. I have browsed the > > >> manual, > > >> > however, I can't find some information. could you give me > > >> some advice? > > >> > > > >> > thanks a lot. > > >> > > > >> > Regards, > > >> > Yujie > > >> > > > >> > > >> > > >> > > >> > ------------------------------------------------------------------------ > > >> Looking for last minute shopping deals? Find them fast with Yahoo! > > >> Search. > > >> < > http://us.rd.yahoo.com/evt=51734/*http://tools.search.yahoo.com/newsearch/category.php?category=shopping > > > > > > > > > > > > > > > > > > > > > -- > Lisandro Dalc?n > --------------- > Centro Internacional de M?todos Computacionales en Ingenier?a (CIMEC) > Instituto de Desarrollo Tecnol?gico para la Industria Qu?mica (INTEC) > Consejo Nacional de Investigaciones Cient?ficas y T?cnicas (CONICET) > PTLC - G?emes 3450, (3000) Santa Fe, Argentina > Tel/Fax: +54-(0)342-451.1594 > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20080205/d54f4472/attachment.htm>
