Thank you Barry, that explains why I couldn't find information about it. I am now going to implement this straight-forward implementation as a first step.
In the long term it would in any case be useful to have a solver that uses H-matrices, such as H2lib. Is there any chance Petsc is thinking about moving to this kind of matrices as well in the future? On Sun, Aug 27, 2017 at 12:54 AM Barry Smith <[email protected]> wrote: > > Toon, > > We don't have any such way of doing this. Note that sparse > factorization packages store the "factors" in specialized data structures > that are unlikely to be acessable to perform such operations as you > describe below. > > I think what you want to do is an over optimization not worth the > coding effort. > > Barry > > > On Aug 25, 2017, at 5:01 AM, Toon Weyens <[email protected]> wrote: > > > > Dear all, > > > > For a Bounday Element Method problem I require the solution of a system > of linear equations with multiple right-hand sides. Though this is a dense > system, I still want to do it via Petsc. Would the best way to do this be > through something such as > > > > -ksp_type preonly -pc_type lu -pc_factor_mat_solver_package mumps ? > > > > Furthermore, I refine my grid in a regular way, which leads to a new > system of equations of size 2N x 2N where N is the original number of > unknowns before refining it. The upper-left matrix A_11 in this new system > is identical to the unrefined matrix (multiplied by 0.5). The other three > blocks A_12, A_21 and A_22 are new: > > > > A_11 A_12 > > A_21 A_22 > > > > The question is now whether knowledge about the unrefined matrix A_11 > can be used to speed up calculation of the refined system? > > > > I was thinking, for example, about using the LU decomposition of A_11 to > calculate the LU decomposition of the entire matrix A using the well-known > formula's > > > > L_21 U_11 = A_21 > > L_11 U_12 = A_12 > > L_22 U_22 = A_22 - L_21 U_12 > > > > where L_21 and U_12 are full matrices, L_11, L_22 are lower triangular > matrices and U_11, U_22 are upper triangular. > > > > Is there any way to do this in Petsc? > > > > Or is there a better thing I can do? > > > > Thanks very much in advance! > > > > Regards. > > > > Dr. Toon Weyens > > ITER Organization > >
