Re: [petsc-users] Implementing of a variable block size BILU preconditioner
This would use the blocks as indicated by MatSetVariableBlockSizes, not by using a matrix format that explicitly blocks? The information it needs is too big/complex to yield to the preconditioner via a call like MatInvertVariableBlockDiagonal. Instead, I would model it off MatFactor and the ILU code. I think it would be okay to go into MatILUFactorSymbolic_SeqAIJ and take a different code path (into your new code) when (variable) block sizes are set. Note that the benefits from this might be marginal -- I think the algorithms will produce effectively identical results and doubt there is much opportunity for performance improvement without changing data structures (at least in the common regimes I can think of). Ali Reza Khaz'ali via petsc-users writes: > Hi, > > I want to implement a variable block size BILU preconditioner in PETSc. > I am wondering if modifying the PCVPBJACOBI preconditioner > (vpbjacobi.c), to get what I want, is a good idea. > > Any help is much appreciated. > > -- > Ali Reza Khaz’ali > Assistant Professor of Petroleum Engineering, > Department of Chemical Engineering > Isfahan University of Technology > Isfahan, Iran
Re: [petsc-users] Implementing of a variable block size BILU preconditioner
Well, you need to start somewhere. It is going to take a combination of this, MatLUFactorSymbolic_SeqAIJ(), MatLUFactorSymbolic_SeqAIJ() and MatLUFactorNumerical_SeqAIJ() to get what you want. Note that one of the first things you need to do is given the MatGetVariableBlockSizes() determine the nonzero pattern of the "variable block" matrix from the nonzero pattern of the SeqAIJ matrix and then do a symbolic factorization on that new "reduced" sparse matrix. Them you do a numerical factorization using the "reduced sparse matrix" factorization. Barry > On Dec 1, 2018, at 4:54 PM, Ali Reza Khaz'ali wrote: > > Hi, > > I want to implement a variable block size BILU preconditioner in PETSc. I am > wondering if modifying the PCVPBJACOBI preconditioner (vpbjacobi.c), to get > what I want, is a good idea. > > Any help is much appreciated. > > -- > Ali Reza Khaz’ali > Assistant Professor of Petroleum Engineering, > Department of Chemical Engineering > Isfahan University of Technology > Isfahan, Iran >
Re: [petsc-users] Implementing of a variable block size BILU preconditioner
There is a reason PETSc does not have variable block matrices. It is messy and rarely a big win. It is doable, ML/Aztec does it, but it is messy. On Sat, Dec 1, 2018 at 6:20 PM Smith, Barry F. via petsc-users < petsc-users@mcs.anl.gov> wrote: > >Well, you need to start somewhere. It is going to take a combination of > this, MatLUFactorSymbolic_SeqAIJ(), MatLUFactorSymbolic_SeqAIJ() and > MatLUFactorNumerical_SeqAIJ() to get what you want. Note that one of the > first things you need to do is given the MatGetVariableBlockSizes() > determine the nonzero pattern of the "variable block" matrix from the > nonzero pattern of the SeqAIJ matrix and then do a symbolic factorization > on that new "reduced" sparse matrix. Them you do a numerical factorization > using the "reduced sparse matrix" factorization. > > Barry > > > > On Dec 1, 2018, at 4:54 PM, Ali Reza Khaz'ali > wrote: > > > > Hi, > > > > I want to implement a variable block size BILU preconditioner in PETSc. > I am wondering if modifying the PCVPBJACOBI preconditioner (vpbjacobi.c), > to get what I want, is a good idea. > > > > Any help is much appreciated. > > > > -- > > Ali Reza Khaz’ali > > Assistant Professor of Petroleum Engineering, > > Department of Chemical Engineering > > Isfahan University of Technology > > Isfahan, Iran > > > >
