Non repeatability issue

Barry Smith bsmith at
Tue Mar 18 08:30:40 CDT 2008

1) Are you sure the -vecscatter_reproduce is working, run with - 
options_left and see if
says the option was not used.

2) did you do the -ksp_rtol 1.e-12 at the same time as the - 
vecscatter_reproduce? They
must be done together.

3) what happens on 1 process? Does it behave exactly the same for two  
identical runs?

4) there is too much going on here to figure out why you get this  
behavior. Can you please
   FIX the continuation parameter and run until Newton converges? Is  
the convergence in
   this case reproduceable? What happens if you only change the  
continuation parameter
   after you have Newton fully converged for the current continuation  
parameter? is that

  5) in the plots can you indicate when the continuation parameter is  
changed? You are
    merging two algorithms (Newton's method and continuation together)  
you cannot hope
    to understand that merged algorithm until you understand each of  
them seperately.


On Mar 18, 2008, at 5:57 AM, Aldo Bonfiglioli wrote:

>> 1)    Have you made runs where you require, say -ksp_rtol 1.e-12  
>> to  eliminate the effects of
>> not solving the linear systems accurately?
> I have performed two runs with ksp_rtol = 1.e-12. The relevant plots  
> are enclosed
> where comparisons are made with PETSc's default for ksp_rtol.
> In one of these two runs Newton even diverges.
> It should however be mentioned that
> at least for some Newton steps, the linear solver does not meet the
> convergence criterion in 2000 linear iterations (I reduced the  
> default).
>> I have added the  argument -vecscatter_reproduce
>> that will cause the receives to always be processed in the same  
>> order  (though order or
>> operations in the MPI reductions may still result in slightly   
>> different convergence histories.)
>>  Hope this helps clear things up,
> I am not sure "-vecscatter_reproduce " has changed the situation much.
> Out of 4 subsequent runs, 2 converge
> while 2 enter a limit cycle I had not seen previously
> (I mean without the -vecscatter_reproduce option).
> The initial solution is the same as that shown in the other plot.
> Aldo
> -- 
> Dr. Aldo Bonfiglioli
> di Ingegneria e Fisica dell'Ambiente (DIFA)
> Universita' della Basilicata
> V.le dell'Ateneo lucano, 10 85100 Potenza ITALY
> tel:+39.0971.205203 fax:+39.0971.205160
> <low_ksp_rtol.pdf><vecscatter_reproduce.pdf>

More information about the petsc-users mailing list