Hi all,
I have parallelized a code in which I use GMRES or Bicgstab solvers with
BlockJacobi preconditioner for a symmetric but not possitive-difinite
system matrix. The problem is that it converges for 150000 DoFs and fewer
(on 1 node with 16 processor) but does'nt converge for larger number of
DoFs for example 500000 or one million (even with 64 processors).
It would be appreciated if you could give me any clue to find out how to
make it converge for large number of DoFs. The following is the error I
usually get.
Thanks
Hamed
----------------------------------------------------
Exception on processing:
--------------------------------------------------------
An error occurred in line <151> of file
</shared/hpc/deal.ii-candi/tmp/unpack/deal.II-v8.4.1/source/lac/petsc_solver.cc>
in function
void dealii::PETScWrappers::SolverBase::solve(const
dealii::PETScWrappers::MatrixBase&, dealii::PETScWrappers::VectorBase&,
const dealii::PETScWrappers::VectorBase&, const
dealii::PETScWrappers::PreconditionerBase&)
The violated condition was:
false
The name and call sequence of the exception was:
SolverControl::NoConvergence (solver_control.last_step(),
solver_control.last_value())
Additional Information:
Iterative method reported convergence failure in step 10000. The residual
in the last step was 1.54204e-06.
This error message can indicate that you have simply not allowed a
sufficiently large number of iterations for your iterative solver to
converge. This often happens when you increase the size of your problem. In
such cases, the last residual will likely still be very small, and you can
make the error go away by increasing the allowed number of iterations when
setting up the SolverControl object that determines the maximal number of
iterations you allow.
The other situation where this error may occur is when your matrix is not
invertible (e.g., your matrix has a null-space), or if you try to apply the
wrong solver to a matrix (e.g., using CG for a matrix that is not symmetric
or not positive definite). In these cases, the residual in the last
iteration is likely going to be large.
--------------------------------------------------------
Aborting!
----------------------------------------------------
ERROR: Uncaught exception in MPI_InitFinalize on proc 1. Skipping
MPI_Finalize() to avoid a deadlock.
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