[petsc-users] SNES stuck with small residual

Thu Sep 24 17:28:03 CDT 2015

On Thu, Sep 24, 2015 at 5:23 PM, Gideon Simpson <gideon.simpson at gmail.com>
wrote:

> Just wondering if anyone has any suggestions for this scenario:
>

I have seen this happen a bunch. Your Newton directions are crap. That
means

  a) you have a crap Jacobian

  b) your Jacobian direction is crap (unlikely here)

  c) your Jacobian is very ill-conditioned

Something to try in order to see what is happening is to start doing Picard
when Newton stalls. If it
converges, then you have something like c) I think. We can try to mitigate
this by NPC. Something
as simple as Newton + NCG or Newton + NRichardson can work.

  Matt

>   0 SNES Function norm 5.979113140046e+02
>     0 KSP preconditioned resid norm 1.609660749629e+03 true resid norm
> 5.979113140046e+02 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 1.083640787055e-06 true resid norm
> 4.070012556358e-04 ||r(i)||/||b|| 6.807050579289e-07
>   1 SNES Function norm 5.106334303399e+02
>     0 KSP preconditioned resid norm 1.304622870569e+03 true resid norm
> 5.106334303399e+02 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 1.542022975926e-06 true resid norm
> 3.284828506619e-04 ||r(i)||/||b|| 6.432850478341e-07
>   2 SNES Function norm 4.522093337153e+02
>     0 KSP preconditioned resid norm 1.017788935768e+03 true resid norm
> 4.522093337153e+02 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 1.338757544659e-06 true resid norm
> 2.556045980853e-04 ||r(i)||/||b|| 5.652351223829e-07
>   3 SNES Function norm 4.042911112972e+02
>     0 KSP preconditioned resid norm 7.996536035697e+02 true resid norm
> 4.042911112972e+02 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 8.612178921208e-07 true resid norm
> 2.026756625099e-04 ||r(i)||/||b|| 5.013112008810e-07
>   4 SNES Function norm 3.618952927134e+02
>     0 KSP preconditioned resid norm 6.392806337991e+02 true resid norm
> 3.618952927134e+02 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 5.099112497936e-07 true resid norm
> 1.605851784448e-04 ||r(i)||/||b|| 4.437338138353e-07
>   5 SNES Function norm 3.239307814846e+02
>     0 KSP preconditioned resid norm 5.205889419531e+02 true resid norm
> 3.239307814846e+02 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 3.364948858968e-07 true resid norm
> 1.326652268287e-04 ||r(i)||/||b|| 4.095480714142e-07
>   6 SNES Function norm 2.899625386925e+02
>     0 KSP preconditioned resid norm 4.305631057215e+02 true resid norm
> 2.899625386925e+02 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 2.472775427751e-07 true resid norm
> 1.094956512355e-04 ||r(i)||/||b|| 3.776199909453e-07
>   7 SNES Function norm 2.596235386610e+02
>     0 KSP preconditioned resid norm 3.606693697722e+02 true resid norm
> 2.596235386610e+02 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 1.804499181789e-07 true resid norm
> 9.162646660567e-05 ||r(i)||/||b|| 3.529204904849e-07
>   8 SNES Function norm 2.178613867932e+02
>     0 KSP preconditioned resid norm 2.791607776778e+02 true resid norm
> 2.178613867932e+02 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 1.269331257925e-07 true resid norm
> 7.151934347788e-05 ||r(i)||/||b|| 3.282791160499e-07
>   9 SNES Function norm 1.541279494063e+02
>     0 KSP preconditioned resid norm 1.781925534106e+02 true resid norm
> 1.541279494063e+02 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 1.095285568305e-07 true resid norm
> 4.530373014757e-05 ||r(i)||/||b|| 2.939358521416e-07
>  10 SNES Function norm 1.361917300390e+02
>     0 KSP preconditioned resid norm 4.801281559143e+01 true resid norm
> 1.361917300390e+02 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 1.158004981151e-07 true resid norm
> 1.216364616255e-05 ||r(i)||/||b|| 8.931266354477e-08
>  11 SNES Function norm 6.951420638296e+00
>     0 KSP preconditioned resid norm 2.808725633599e+00 true resid norm
> 6.951420638296e+00 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 2.361764665651e-09 true resid norm
> 7.088079744061e-07 ||r(i)||/||b|| 1.019659162188e-07
>  12 SNES Function norm 3.249486326694e-03
>     0 KSP preconditioned resid norm 1.388995922430e-03 true resid norm
> 3.249486326694e-03 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 1.757348050151e-12 true resid norm
> 3.473453149942e-10 ||r(i)||/||b|| 1.068923762322e-07
>  13 SNES Function norm 4.590368792536e-05
>     0 KSP preconditioned resid norm 4.360884570719e-06 true resid norm
> 4.590368792536e-05 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 3.926789585311e-15 true resid norm
> 1.102338507065e-12 ||r(i)||/||b|| 2.401416001385e-08
>  14 SNES Function norm 4.422797479565e-05
>     0 KSP preconditioned resid norm 5.831925614907e-06 true resid norm
> 4.422797479565e-05 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 5.584144701532e-15 true resid norm
> 1.478006791605e-12 ||r(i)||/||b|| 3.341791701821e-08
>  15 SNES Function norm 4.371345326958e-05
>     0 KSP preconditioned resid norm 4.897666437748e-06 true resid norm
> 4.371345326958e-05 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 4.080247182926e-15 true resid norm
> 1.236587295819e-12 ||r(i)||/||b|| 2.828848336902e-08
>  16 SNES Function norm 4.348609553058e-05
>     0 KSP preconditioned resid norm 3.738450099362e-06 true resid norm
> 4.348609553058e-05 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 3.655406222015e-15 true resid norm
> 9.403440338690e-13 ||r(i)||/||b|| 2.162401619174e-08
>  17 SNES Function norm 4.324907311342e-05
>     0 KSP preconditioned resid norm 5.296206632183e-06 true resid norm
> 4.324907311342e-05 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 5.018283198612e-15 true resid norm
> 1.334862856428e-12 ||r(i)||/||b|| 3.086454252850e-08
>  18 SNES Function norm 4.324904992696e-05
>     0 KSP preconditioned resid norm 5.289306428405e-06 true resid norm
> 4.324904992696e-05 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 5.691985954854e-15 true resid norm
> 1.335680822478e-12 ||r(i)||/||b|| 3.088347200075e-08
>  19 SNES Function norm 4.324904992565e-05
>     0 KSP preconditioned resid norm 5.289311834250e-06 true resid norm
> 4.324904992565e-05 ||r(i)||/||b|| 1.000000000000e+00
>     1 KSP preconditioned resid norm 5.455286406170e-15 true resid norm
> 1.337387995906e-12 ||r(i)||/||b|| 3.092294508677e-08
>
>
>
> At this point, it terminates with a diverged line search.
>
>
> -gideon
>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20150924/54c269e0/attachment-0001.html>