[petsc-users] Convergence of AMG

[Manav Bhatia]

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.