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

[Gideon Simpson]

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 <mailto: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 
> 

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