[petsc-users] pcfieldsplit for a composite dm with multiple subfields

[Barry Smith]

  Please run with the -snes_fd and one level of grid sequencing (where Newton was having trouble converging on the second level) with -snes_monitor -ksp_monitor_true_residual and send the output. Too much speculation and not enough data.

   Barry


> On Sep 9, 2015, at 11:14 AM, Gideon Simpson <gideon.simpson at gmail.com> wrote:
> 
> Checking the Jacobian, this is a pretty standard output:
> 
>       Testing hand-coded Jacobian, if the ratio is O(1.e-8), the hand-coded Jacobian is probably correct.
>     Finite difference Jacobian
>     Hand-coded Jacobian
>     Hand-coded minus finite difference Jacobian
>     6.08281e-10 = ||J - Jfd||//J|| 0.000151055  = ||J - Jfd||
> 
> 
> Things look favorable in terms of relative difference, but the absolute difference is a bit more suspect.
> 
> -gideon
> 
>> On Sep 8, 2015, at 11:49 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>> 
>>> 
>>> On Sep 8, 2015, at 10:28 PM, Gideon Simpson <gideon.simpson at gmail.com> wrote:
>>> 
>>> I should clarify, in that run, I ran with the analytic jacobian, but I did not use -snes_mf_operator.  If I use that flag, the performance is a bit different.  In particular, the true residual norms are not as good.  How should I interpret that?
>> 
>>  The "analytic Jacobians" are wrong. Of course, that is easy to say, the hard part is figuring out exactly what entries are wrong.
>> 
>>  You can try the following options. They are experimental so may be flaky run with the options below (but not -snes_fd or -snes_mf_operators)
>> 
>> -snes_check_jacobian 
>> -snes_check_jacobian_view 
>> 
>