Here I use MPI with multi-threads. On Friday, October 5, 2018 at 4:40:55 PM UTC-4, Ki-Tae Kim wrote: > > When I solve a very large system (positive definite and symmetric), dofs > over 10,000,000, PETScWrappers::SolverCG solver termintates with an error > of convergence failure in step 10000 even though the maximum number of > iteration is set over 10000. > > I have tested using different maximum numbers of iteration setting as > follows (just for test, the tolerence is set as a very small number): > > > ===================================================================================================== > For example: > > If the maximum number of iteration is set by 100, > > In code: > ... > SolverControl solver_control (100, > > 1e-100*pdata.system_rhs.l2_norm()); > PETScWrappers::SolverCG solver(solver_control, > > mpi_communicator); > ... > > Result: > Solve the system by CG method: > DEAL::Starting value 1.07201 > ERROR: Uncaught exception in MPI_InitFinalize on proc 0. Skipping > MPI_Finalize() to avoid a deadlock. > > > ---------------------------------------------------- > Exception on processing: > > -------------------------------------------------------- > An error occurred in line <138> of file > </tigress/CHIARAMONTE/ktk/src/dealii-9.0.0/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 > Additional information: > Iterative method reported convergence failure in step 62. The residual in > the last step was 4.09564e-83. > > 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. > -------------------------------------------------------- > > If the maximum number of iteration is set by 1000, > > In code: > ... > SolverControl solver_control (1000, > > 1e-100*pdata.system_rhs.l2_norm()); > PETScWrappers::SolverCG solver(solver_control, > > mpi_communicator); > ... > > Result: > Solve the system by CG method: > DEAL::Starting value 1.07201 > ERROR: Uncaught exception in MPI_InitFinalize on proc 0. Skipping > MPI_Finalize() to avoid a deadlock. > > > ---------------------------------------------------- > Exception on processing: > > -------------------------------------------------------- > An error occurred in line <138> of file > </tigress/CHIARAMONTE/ktk/src/dealii-9.0.0/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 > Additional information: > Iterative method reported convergence failure in step 62. The residual in > the last step was 4.09564e-83. > > 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. > -------------------------------------------------------- > > ===================================================================================================== > > As you can see above, it fails in step 62 in both cases even though they > are set by 100 and 1000. > > Could anyone know the problem and how to set the maximum number of > iteration for PETScWrappers::SolverCG? > > I appreciate your help! > > Thanks. >
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