Hi Bruno and Jean
Thanks a lot for the answers. Sorry to reply this late, was busy with other PhD duties. I did have a look at KINSOL when encountered the problem for the first time, I think it would be a convenient tool for more stable nonlinear problems.
@Jean: here is the dealllog output
Initial residual: 0.1875
Number of active cells: 16
Number of degrees of freedom: 25
===== Solving torsion function for p = 3 =====
DEAL:cg::Starting value 0.187500
DEAL:cg::Convergence step 3 value 1.15076e-17
3 CG steps
DEAL::Bracketing phase: 1
DEAL::1.00000 8.15283e+16 7.41104e+07 0 0 -0.00395508
DEAL::Sectioning phase: 2
DEAL::0.00000 0.0175781 -0.0351563 1 0
DEAL::1.00000 8.15283e+16 7.41104e+07 0 0
DEAL::0.300000 6.60380e+14 6.66994e+06 0 0
DEAL::Sectioning phase: 3
DEAL::0.00000 0.0175781 -0.0351563 1 0
DEAL::0.300000 6.60380e+14 6.66994e+06 0 0
DEAL::0.0900000 5.34907e+12 600294. 0 0
DEAL::Sectioning phase: 4
DEAL::0.00000 0.0175781 -0.0351563 1 0
DEAL::0.0900000 5.34907e+12 600294. 0 0
DEAL::0.0270000 4.33275e+10 54026.5 0 0
DEAL::Sectioning phase: 5
DEAL::0.00000 0.0175781 -0.0351563 1 0
DEAL::0.0270000 4.33275e+10 54026.5 0 0
DEAL::0.00810000 3.50948e+08 4862.35 0 0
DEAL::Sectioning phase: 6
DEAL::0.00000 0.0175781 -0.0351563 1 0
DEAL::0.00810000 3.50948e+08 4862.35 0 0
DEAL::0.00243000 2.84228e+06 437.579 0 0
DEAL::Sectioning phase: 7
DEAL::0.00000 0.0175781 -0.0351563 1 0
DEAL::0.00243000 2.84228e+06 437.579 0 0
DEAL::0.000729000 22986.6 39.3502 0 0
DEAL::Sectioning phase: 8
DEAL::0.00000 0.0175781 -0.0351563 1 0
DEAL::0.000729000 22986.6 39.3502 0 0
DEAL::0.000218700 182.984 3.50952 0 0
DEAL::Sectioning phase: 9
DEAL::0.00000 0.0175781 -0.0351563 1 0
DEAL::0.000218700 182.984 3.50952 0 0
DEAL::6.56100e-05 1.20929 0.283865 0 0
DEAL::Sectioning phase: 10
DEAL::0.00000 0.0175781 -0.0351563 1 0
DEAL::6.56100e-05 1.20929 0.283865 0 0
DEAL::1.96830e-05 0.00110320 -0.00644436 1 1
DEAL::Satisfied both Wolfe conditions.
DEAL:cg::Starting value 0.0469723
DEAL:cg::Convergence step 3 value 7.79533e-08
3 CG steps
DEAL::Bracketing phase: 1
DEAL::1.00000 2.86692e+32 6.48676e+14 0 0 -0.000248220
DEAL::Sectioning phase: 2
DEAL::0.00000 0.00110320 -0.00220640 1 0
DEAL::1.00000 2.86692e+32 6.48676e+14 0 0
DEAL::0.300000 2.32221e+30 5.83808e+13 0 0
DEAL::Sectioning phase: 3
DEAL::0.00000 0.00110320 -0.00220640 1 0
DEAL::0.300000 2.32221e+30 5.83808e+13 0 0
DEAL::0.0900000 1.88099e+28 5.25428e+12 0 0
DEAL::Sectioning phase: 4
DEAL::0.00000 0.00110320 -0.00220640 1 0
DEAL::0.0900000 1.88099e+28 5.25428e+12 0 0
DEAL::0.0270000 1.52360e+26 4.72885e+11 0 0
DEAL::Sectioning phase: 5
DEAL::0.00000 0.00110320 -0.00220640 1 0
DEAL::0.0270000 1.52360e+26 4.72885e+11 0 0
DEAL::0.00810000 1.23412e+24 4.25597e+10 0 0
. . .
DEAL::Sectioning phase: 17
DEAL::0.00000 0.00110320 -0.00220640 1 0
DEAL::1.43489e-08 22.1753 0.178932 0 0
DEAL::4.30467e-09 0.445889 0.0240882 0 0
DEAL::Sectioning phase: 18
DEAL::0.00000 0.00110320 -0.00220640 1 0
DEAL::4.30467e-09 0.445889 0.0240882 0 0
DEAL::1.29140e-09 0.0153440 0.00315777 0 0
DEAL::Sectioning phase: 19
DEAL::0.00000 0.00110320 -0.00220640 1 0
DEAL::1.29140e-09 0.0153440 0.00315777 0 0
DEAL::3.87420e-10 0.00102256 -0.000824328 1 1
DEAL::Satisfied both Wolfe conditions.
DEAL:cg::Starting value 0.0452230
DEAL:cg::Convergence step 3 value 6.54715e-07
3 CG steps
DEAL::Bracketing phase: 1
DEAL::1.00000 2.67799e+30 5.53778e+13 0 0 -0.000230076
DEAL::Sectioning phase: 2
DEAL::0.00000 0.00102256 -0.00204512 1 0
DEAL::1.00000 2.67799e+30 5.53778e+13 0 0
DEAL::0.300000 2.16917e+28 4.98400e+12 0 0
DEAL::Sectioning phase: 3
DEAL::0.00000 0.00102256 -0.00204512 1 0
DEAL::0.300000 2.16917e+28 4.98400e+12 0 0
DEAL::0.0900000 1.75703e+26 4.48560e+11 0 0
DEAL::Sectioning phase: 4
DEAL::0.00000 0.00102256 -0.00204512 1 0
DEAL::0.0900000 1.75703e+26 4.48560e+11 0 0
DEAL::0.0270000 1.42319e+24 4.03704e+10 0 0
DEAL::Sectioning phase: 5
DEAL::0.00000 0.00102256 -0.00204512 1 0
DEAL::0.0270000 1.42319e+24 4.03704e+10 0 0
DEAL::0.00810000 1.15278e+22 3.63333e+09 0 0
DEAL::Sectioning phase: 6
DEAL::0.00000 0.00102256 -0.00204512 1 0
DEAL::0.00810000 1.15278e+22 3.63333e+09 0 0
DEAL::0.00243000 9.33741e+19 3.26998e+08 0 0
DEAL::Sectioning phase: 7
DEAL::0.00000 0.00102256 -0.00204512 1 0
DEAL::0.00243000 9.33741e+19 3.26998e+08 0 0
DEAL::0.000729000 7.56303e+17 2.94293e+07 0 0
DEAL::Sectioning phase: 8
DEAL::0.00000 0.00102256 -0.00204512 1 0
DEAL::0.000729000 7.56303e+17 2.94293e+07 0 0
DEAL::0.000218700 6.12531e+15 2.64847e+06 0 0
DEAL::Sectioning phase: 9
DEAL::0.00000 0.00102256 -0.00204512 1 0
DEAL::0.000218700 6.12531e+15 2.64847e+06 0 0
DEAL::6.56100e-05 4.95950e+13 238314. 0 0
DEAL::Sectioning phase: 10
DEAL::0.00000 0.00102256 -0.00204512 1 0
DEAL::6.56100e-05 4.95950e+13 238314. 0 0
DEAL::1.96830e-05 4.01179e+11 21433.9 0 0
. . .
DEAL::Sectioning phase: 49
DEAL::6.58615e-10 0.000743997 -0.00137850 1 0
DEAL::6.58615e-10 0.000743997 -0.00137850 1 0
DEAL::6.58615e-10 0.000743997 -0.00137850 1 0
DEAL::Sectioning phase: 50
DEAL::6.58615e-10 0.000743997 -0.00137850 1 0
DEAL::6.58615e-10 0.000743997 -0.00137850 1 0
DEAL::6.58615e-10 0.000743997 -0.00137850 1 0
DEAL::Sectioning phase: 51
DEAL::6.58615e-10 0.000743997 -0.00137850 1 0
DEAL::6.58615e-10 0.000743997 -0.00137850 1 0
DEAL::6.58615e-10 0.000743997 -0.00137850 1 0
--------------------------------------------------------
An error occurred in line <457> of file </home/jmrug/deal.ii-candi/deal.II-v9.1.1/include/deal.II/optimization/line_minimization.h> in function
NumberType dealii::LineMinimization::poly_fit(NumberType, NumberType, NumberType, NumberType, NumberType, NumberType, const dealii::FiniteSizeHistory<NumberType>&, const dealii::FiniteSizeHistory<NumberType>&, const dealii::FiniteSizeHistory<NumberType>&, std::pair<_FIter, _FIter>) [with NumberType = double]
The violated condition was:
bounds.first < bounds.second
Additional information:
Incorrect bounds
The last few LS iterations do look strange, they barely changed.
When run with more dofs on the same mesh (16 cells, 81 dofs) I get convergence failure. There is a regularization parameter epsilon=1e-5, with larger epsilon on the same mesh, I get bounds error again. For smaller p like 3-5, this epsilon should actually be enough for regularization...
Any help is highly appreciated.
Best wishes,
Julie