From 4fdf7f4d2f98c3e45007993b08473b4025bddcf7 Mon Sep 17 00:00:00 2001 From: bangerth Date: Thu, 22 May 2008 20:38:35 +0000 Subject: [PATCH] Comment more. git-svn-id: https://svn.dealii.org/trunk@16171 0785d39b-7218-0410-832d-ea1e28bc413d --- deal.II/examples/step-33/doc/results.dox | 66 +++++++++++++++++++++--- 1 file changed, 60 insertions(+), 6 deletions(-) diff --git a/deal.II/examples/step-33/doc/results.dox b/deal.II/examples/step-33/doc/results.dox index e297177f33..b108a71dfc 100644 --- a/deal.II/examples/step-33/doc/results.dox +++ b/deal.II/examples/step-33/doc/results.dox @@ -133,7 +133,9 @@ This output reports the progress of the Newton iterations and the time stepping. Note that our implementation of the Newton iteration indeed shows the expected quadratic convergence order: the norm of the nonlinear residual in each step is roughly the norm of the previous step squared. This leads to -the very rapid convergence we can see here. +the very rapid convergence we can see here. This holds at least for +times up to $t=8.32$ at which time the nonlinear iteration reports a +lack of convergence; the cause and possible remedies are discussed below. The result of running these computations is a bunch of output files that we can pass to our visualization program of choice. When we collate them into a @@ -167,12 +169,64 @@ more importantly we should take smaller steps whenever we can't solve the problem at hand any more with Newton's method. The latter is what happens to the calculation the screen output of which was shown above: @code +... + +T=8.3 + Number of active cells: 2314 + Number of degrees of freedom: 10264 + + NonLin Res Lin Iter Lin Res + _____________________________________ + 4.069e-02 0018 3.74e-12 + 3.570e-04 0020 6.83e-15 + 8.349e-07 0020 2.51e-17 + 2.858e-11 (converged) + +T=8.32 + Number of active cells: 2320 + Number of degrees of freedom: 10292 + + NonLin Res Lin Iter Lin Res + _____________________________________ + 5.607e-02 0240 4.36e-12 + 5.807e-04 0300 1.54e-05 + 1.538e-05 0300 1.22e-05 + 1.218e-05 0300 9.15e-06 + 9.146e-06 0300 4.27e-06 + 4.264e-06 0300 3.69e-06 + 3.693e-06 0300 3.31e-06 + 3.308e-06 0300 2.81e-06 + 2.809e-06 0300 2.77e-07 + 2.781e-07 0300 2.33e-07 + 2.328e-07 0300 1.89e-07 + + +---------------------------------------------------- +Exception on processing: +-------------------------------------------------------- +An error occurred in line <3119> of file in function + void ConservationLaw::run() [with int dim = 2] +The violated condition was: + nonlin_iter <= 10 +The name and call sequence of the exception was: + ExcMessage ("No convergence in nonlinear solver") +Additional Information: +No convergence in nonlinear solver +-------------------------------------------------------- + +Aborting! +---------------------------------------------------- @endcode -If this happens, it would be nice if we could either (i) detect the -problem up front and reduce the time step before we even start the -time step, or (ii) accept the failure at this time step and then -simply start over from the previous time step trying with a reduced -step size. + +From looking at the graphical output, it isn't immediately clear if +there is a physical event that triggers this breakdown. However, +whatever the matter, the solver should certainly not just break down. + +If this happens nevertheless, it would be nice if we could either (i) +detect the problem up front and reduce the time step before we even +start the time step, or (ii) accept the failure at this time step and +then simply start over from the previous time step trying with a +reduced step size.

Stabilization

-- 2.39.5