Dear Arndt
Thank you for answer. I want to solve the system during a time step using a
split method. First assembling block(0,0) and solving the displacement
field, then using the updated displacement, the second field must be solved
and so block(1,1) of system matrix is determined. I have not any problem
when working with BlockSparseMatrix<double>
<https://www.dealii.org/8.4.0/doxygen/deal.II/classBlockSparseMatrix.html>
system_matrix and a BlockVector<double>
<https://www.dealii.org/8.4.0/doxygen/deal.II/classBlockVector.html>
solution, for splitting the system (similar to step-22). The problem occurs
when working with Trilinos.
For example when a direct solver is used as bellow,
*if* (direct_solver)
{
SolverControl cn;
TrilinosWrappers::SolverDirect solver(cn);
solver.*solve*(system_pde_matrix.block(0,0),
newton_update.block(0), system_pde_residual.block(0));
constraints_update.distribute(newton_update);
*return* 1;
}
block(0,0) of system matrix and block(0) of residual and Newton update
vectors are selected but all block is solved simultaneously!! So I cant
solve specific block using direct solver and it is the first problem.
The second problem is when working with iterative solver. I cant set an AMG
Precondition for specific block of the system. For example I define a class
like this:
*template* <*class* *PreconditionerA*>
*class* BlockDiagonalPreconditioner_one
{
*public*:
*BlockDiagonalPreconditioner_one*(*const* LA::MPI::BlockSparseMatrix &M,
*const* *PreconditionerA* &pre_A)
: matrix(M),
prec_A (pre_A)
{
}
*void* *vmult* (LA::MPI::BlockVector &dst,
*const* LA::MPI::BlockVector &src) *const*
{
prec_A.vmult(dst.block(0), src.block(0));
}
*const* LA::MPI::BlockSparseMatrix &matrix;
*const* *PreconditionerA* &prec_A;
};
for solving block(0,0) as,
BlockDiagonalPreconditioner_one<LA::MPI::PreconditionAMG>
preconditioner(system_pde_matrix.block(0,0), preconditioner_solid);
solver.*solve*(system_pde_matrix.block(0,0), newton_update.block(0),
system_pde_residual.block(0), preconditioner);
But there are two errors:
1) no matching function for call to
‘BlockDiagonalPreconditioner_one<dealii::TrilinosWrappers::PreconditionAMG>::BlockDiagonalPreconditioner_one(dealii::BlockMatrixBase<dealii::TrilinosWrappers::SparseMatrix>::BlockType&,
dealii::LinearAlgebraTrilinos::MPI::PreconditionAMG&)’
2) Invalid arguments '
Candidates are:
void solve(const #10000 &, dealii::TrilinosWrappers::MPI::BlockVector &,
const dealii::TrilinosWrappers::MPI::BlockVector &, const #10001 &)
the first error may be due to sending block(0,0) of TrilinosWrappers
BlockMatrix as first argument of *BlockDiagonalPreconditioner_one*
constructor.
Finally how I can set precondition for specific block and how I can solve
that block when working with TrilinosWrappers?
Best
Pasha
On Monday, July 25, 2016 at 10:18:42 PM UTC+4:30, Daniel Arndt wrote:
>
> Pasha,
>
> there are tutorial programs, such as step-22[1], that use BlockMatrices
> and solve for individual blocks.
> What exactly is the problem you are facing? Does it have anything to do
> with Trilinos objects or is it a conceptual problem?
>
> Can you tell us how exactly you want to split solving your system?
>
> Best,
> Daniel
>
> [1] https://www.dealii.org/8.4.0/doxygen/deal.II/step_22.html
>
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