Thank you for your help. what is strange to me is that the assembly part 
has not changed for parallelization except an "if 
(cell->is_locally_owned())" command at the beginning of the loop over 
cells. So since the non-parallel code with the same assembly is solved with 
SolverCG, the parallel one should be solved as well !!!. I don't know what 
is affected by parallelization which incapacitates the SolverCG.!!

which solvers do you think I can examin and see if they can be used instead 
of SolverCG?


On Monday, October 17, 2016 at 8:57:47 AM UTC-5, Daniel Arndt wrote:
> Hamed,
> running your code with a Trilinos installation alone fails for me in line 
> 1617 with
> An error occurred in line <279> of file 
> </mnt/data/darndt/Sources/dealii/source/lac/trilinos_solver.cc> in function
>     void dealii::TrilinosWrappers::SolverBase::do_solve(const 
> dealii::TrilinosWrappers::PreconditionBase&)
> The violated condition was:
>     false
> Additional information:
>     AztecOO::Iterate error code -2: numerical breakdown
> and the same for no preconditioner. The same holds for PETSc. It seems 
> that you should review if this matrix is assembled correctly and that CG is 
> appropriate, i.e. is this matrix symmetric and positive definite?
> I can't reproduce your error
> "PETSC ERROR: Caught signal number 11 SEGV: Segmentation Violation, 
> probably memory access out of range"
> running with a developer version.
> Best,
> Daniel
> Am Montag, 17. Oktober 2016 04:47:32 UTC+2 schrieb Wolfgang Bangerth:
>> On 10/16/2016 03:46 PM, Hamed Babaei wrote: 
>> > Another point I need to mention is that I had the same problem when as 
>> my 
>> > first try of parallelization, I paralleled a much simpler code, the 
>> step-25, 
>> > based on the step-40 . 
>> > I received the same Segmentation Violation error from Petsc. At that 
>> time, I 
>> > replaced PreconditionerAMG with PreconditionerJacobi and the problem 
>> resolved. 
>> This does not help right now, but as a general rule, it is far simpler to 
>> debug things when you have a small, simple program that when you have a 
>> large, 
>> complicated one. In your case, you had a problem you didn't understand, 
>> and 
>> you chose to address it in a way that papered over it, rather than 
>> properly 
>> fixed it based on an understanding of what is going on. It is a truism 
>> that 
>> this sort of issue will come back at some time. 
>> In other words, if you have a problem, debug it until you understand what 
>> the 
>> problem is, and then fix it the right way. Don't paper over it. 
>> Best 
>>   W. 
>> -- 
>> ------------------------------------------------------------------------ 
>> Wolfgang Bangerth          email:                 bang...@colostate.edu 
>>                             www: http://www.math.colostate.edu/~bangerth/ 

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