Hello,
I'm sorry it took so long.
There were actually a couple of mistakes in my jacobian and residual.
Now for the small problem without specifying any options I get:
> Running ./example-opt
>
> Mesh Information:
> mesh_dimension()=3
> spatial_dimension()=3
> n_nodes()=66
> n_local_nodes()=66
> n_elem()=20
> n_local_elem()=20
> n_active_elem()=20
> n_subdomains()=1
> n_partitions()=1
> n_processors()=1
> n_threads()=1
> processor_id()=0
>
> EquationSystems
> n_systems()=1
> System #0, "StVen"
> Type "NonlinearImplicit"
> Variables={ "u" "v" "z" }
> Finite Element Types="LAGRANGE"
> Approximation Orders="FIRST"
> n_dofs()=198
> n_local_dofs()=198
> n_constrained_dofs()=18
> n_local_constrained_dofs()=18
> n_vectors()=1
> n_matrices()=1
> DofMap Sparsity
> Average On-Processor Bandwidth <= 39.4545
> Average Off-Processor Bandwidth <= 0
> Maximum On-Processor Bandwidth <= 54
> Maximum Off-Processor Bandwidth <= 0
> DofMap Constraints
> Number of DoF Constraints = 18
> Average DoF Constraint Length= 0
>
> NL step 0, |residual|_2 = 3.464102e-05
> NL step 1, |residual|_2 = 3.126867e-05
> NL step 2, |residual|_2 = 2.835742e-05
> NL step 3, |residual|_2 = 2.579682e-05
> NL step 4, |residual|_2 = 2.351091e-05
> NL step 5, |residual|_2 = 2.144758e-05
> NL step 6, |residual|_2 = 1.957083e-05
> NL step 7, |residual|_2 = 1.785531e-05
> NL step 8, |residual|_2 = 1.628262e-05
> NL step 9, |residual|_2 = 1.463259e-05
> NL step 10, |residual|_2 = 1.280174e-05
> NL step 11, |residual|_2 = 1.073276e-05
> NL step 12, |residual|_2 = 8.355152e-06
> NL step 13, |residual|_2 = 7.606801e-06
> NL step 14, |residual|_2 = 9.503420e-11
> NL step 15, |residual|_2 = 2.354762e-15
> StVen system solved at nonlinear iteration 15 , final nonlinear residual
> norm: 2.354762e-15
I get faster convergence with e.g. -snes_linesearch_type basic -ksp_rtol 1e-4:
> NL step 0, |residual|_2 = 3.464102e-05
> NL step 1, |residual|_2 = 2.417540e-04
> NL step 2, |residual|_2 = 6.174706e-08
> NL step 3, |residual|_2 = 3.577768e-12
> NL step 4, |residual|_2 = 7.687278e-17
> StVen system solved at nonlinear iteration 4 , final nonlinear residual norm:
> 7.687278e-17
I think it would be fine to use these last options also on a finer mesh then.
It finally looks like I don't need JFNK.
Thanks!
Lorenzo
On Nov 26, 2013, at 8:42 PM, Derek Gaston wrote:
> On Tue, Nov 26, 2013 at 11:59 AM, Dmitry Karpeyev <[email protected]> wrote:
> LU, naturally, should do better, and we should at least see quicker linear
> convergence.
> If not, it's an indication that your problem is singular.
>
> LU should only take 1 (ish) linear iteration.
>
> However, I still suspect that the issue here is that his Jacobian is wrong...
> which accounts for the degraded nonlinear convergence.
>
> Lorenzo: Have you double checked your Jacobian statements? Have you checked
> them against your friend doing FEAP? Your statements should look very
> similar to theirs...
>
> Derek
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