Barry,
Here are some quick numbers with the following options on 4 CPUs and 543,606
dofs:
-mg_levels_ksp_max_it 4 -pc_gamg_square_graph 1 -pc_gamg_threshold 0.
#levels | #KSP Iters
———————————
2 | 18
3 | 18
4 | 40
5 | 59
-Manav
> On Oct 29, 2018, at 2:06 PM, Smith, Barry F. <[email protected]> wrote:
>
>
> 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 <[email protected]> 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 <[email protected]> wrote:
>>>
>>> Manav Bhatia <[email protected]> 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.
>>
>
