Dear all,
  I am working on acoustic wave simulation through PETSc wrapper, it gives
the error message:
Mesh Info
Number of active cells:5144
Number of degrees of freedom:20833

Exception on processing:

An error occurred in line <148> of file
</project/cacds/build/dealii-9.2.0/source/lac/> in function
    void dealii::PETScWrappers::SolverBase::solve(const
dealii::PETScWrappers::MatrixBase&, dealii::PETScWrappers::VectorBase&,
const dealii::PETScWrappers::VectorBase&, const
The violated condition was:
Additional information:
Iterative method reported convergence failure in step 65. The residual in
the last step was 0.00295038.

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.

I also wrote a single thread CG version, which converges well. The
preconditioner in the parallel version is blockJacobi but the single thread
version I used is SSOR. Does it matter to the convergence? Thank you!
Best regards,
Yuesu Jin,
Ph.D student,
University of Houston,
College of Natural Sciences and Mathematics,
Department of Earth and Atmospheric Sciences,
Houston, Texas 77204-5008

The deal.II project is located at
For mailing list/forum options, see
You received this message because you are subscribed to the Google Groups 
"deal.II User Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
To view this discussion on the web visit

Reply via email to