[petsc-users] Convergence of AMG

[Smith, Barry F.]

  Exactly how much does it increase with number of levels? Send a chart number of levels and number of iterations. With say -mg_levels_ksp_maxit 4

   Thanks

   Barry




> On Oct 29, 2018, at 12:59 PM, Manav Bhatia <bhatiamanav at gmail.com> wrote:
> 
> Thanks for the clarification. 
> 
> I also observed that the number of KSP iterations increases with an increase in the levels of AMG. Is this true, in general, for all/most applications? 
> 
> -Manav
> 
>> On Oct 29, 2018, at 12:53 PM, Jed Brown <jed at jedbrown.org> wrote:
>> 
>> Manav Bhatia <bhatiamanav at gmail.com> writes:
>> 
>>> Thanks, Jed. 
>>> 
>>> The description says: “ Square the graph, ie. compute A'*A before aggregating it"
>>> 
>>> What is A here? 
>> 
>> The original matrix, or its "graph" (your 6x6 blocks condensed to scalars).
>> 
>>> What is the impact of setting this to 0, which led to a very significant increase in the CPU time in my case? 
>> 
>> The aggregates are formed on the connectivity of your original matrix,
>> so root nodes are aggregated only with their first neighbors, resulting
>> in slower coarsening.
>