> On Jul 13, 2016, at 11:05 AM, Matthew Knepley <[email protected]> wrote:
>
> On Wed, Jul 13, 2016 at 10:34 AM, Hoang Giang Bui <[email protected]> wrote:
> Thanks Barry
>
> This is a good comment. Since material behaviour depends very much on the
> trajectory of the solution. I suspect that the error may concatenate during
> time stepping.
>
> I have re-run the simulation as you suggested and post the log file here:
> https://www.dropbox.com/s/d6l8ixme37uh47a/log13Jul16?dl=0
>
> However, I did not get what -ksp_monitor_true_solution used for? I see that I
> have the same log that I had before.
My mistake. I didn't mean that option.
>
> That option is showing the last two numbers in these lines
>
> 0 KSP preconditioned resid norm 1.150038785083e+00 true resid norm
> 8.673040929526e+07 ||r(i)||/||b|| 1.000000000000e+00
>
> Notice that there are 7 orders of magnitude between the apparent residual
> (using the preconditioner), and the actual residual, Ax - b.
> You are using Hypre, and this generally means the Hypre coarse grid operator
> is crap. Please
>
> a) Try ML or GAMG and look at the output again
>
> b) Try MUMPS, although you have 200 nonzeros/row so that fill-in might be
> extreme.
>
> The consequence is that you solve to what you think is machine precision
> (1e-13), but all you really get is (1e-4), so I can understand
> why the trajectory is completely different.
>
You can compare the final true residual norm at each iteration when using
MUMPS with what you get with hypre to see if MUMPS is able to give you a
smaller residual.
Barry
> Matt
>
> 1 KSP preconditioned resid norm 5.202876635759e-01 true resid norm
> 2.037005052213e+08 ||r(i)||/||b|| 2.348663022307e+00
> 2 KSP preconditioned resid norm 3.386127782775e-01 true resid norm
> 1.762196838305e+08 ||r(i)||/||b|| 2.031809664712e+00
> 3 KSP preconditioned resid norm 2.334102526025e-01 true resid norm
> 1.027451552306e+08 ||r(i)||/||b|| 1.184649721655e+00
> 4 KSP preconditioned resid norm 1.791251896569e-01 true resid norm
> 7.709961160729e+07 ||r(i)||/||b|| 8.889570824556e-01
> 5 KSP preconditioned resid norm 1.338763110903e-01 true resid norm
> 7.416954924746e+07 ||r(i)||/||b|| 8.551735181482e-01
> 6 KSP preconditioned resid norm 8.064262880339e-02 true resid norm
> 5.164444100149e+07 ||r(i)||/||b|| 5.954594405945e-01
> 7 KSP preconditioned resid norm 4.635705318709e-02 true resid norm
> 2.934800965373e+07 ||r(i)||/||b|| 3.383820034081e-01
> 8 KSP preconditioned resid norm 2.772133866748e-02 true resid norm
> 1.528356929458e+07 ||r(i)||/||b|| 1.762192686368e-01
> 9 KSP preconditioned resid norm 1.746753670007e-02 true resid norm
> 1.011788107951e+07 ||r(i)||/||b|| 1.166589799555e-01
> 10 KSP preconditioned resid norm 1.090702407895e-02 true resid norm
> 5.487922954253e+06 ||r(i)||/||b|| 6.327564920823e-02
> 11 KSP preconditioned resid norm 7.298748576067e-03 true resid norm
> 3.635843038640e+06 ||r(i)||/||b|| 4.192120235779e-02
> 12 KSP preconditioned resid norm 5.263606789063e-03 true resid norm
> 2.556946903793e+06 ||r(i)||/||b|| 2.948155006496e-02
> 13 KSP preconditioned resid norm 3.653208280595e-03 true resid norm
> 1.955721190606e+06 ||r(i)||/||b|| 2.254942881623e-02
> 14 KSP preconditioned resid norm 2.344759624903e-03 true resid norm
> 1.161259621408e+06 ||r(i)||/||b|| 1.338930175522e-02
> 15 KSP preconditioned resid norm 1.394564491254e-03 true resid norm
> 7.455856541894e+05 ||r(i)||/||b|| 8.596588673428e-03
> 16 KSP preconditioned resid norm 9.523395328600e-04 true resid norm
> 4.383808867461e+05 ||r(i)||/||b|| 5.054523440028e-03
> 17 KSP preconditioned resid norm 7.226014371144e-04 true resid norm
> 2.463564216053e+05 ||r(i)||/||b|| 2.840484941869e-03
> 18 KSP preconditioned resid norm 5.312593384754e-04 true resid norm
> 2.332075376781e+05 ||r(i)||/||b|| 2.688878555665e-03
> 19 KSP preconditioned resid norm 3.987403871945e-04 true resid norm
> 1.524236218549e+05 ||r(i)||/||b|| 1.757441514383e-03
> 20 KSP preconditioned resid norm 3.024350484979e-04 true resid norm
> 1.113568566173e+05 ||r(i)||/||b|| 1.283942477870e-03
> 21 KSP preconditioned resid norm 2.181724540430e-04 true resid norm
> 9.095158030900e+04 ||r(i)||/||b|| 1.048670022983e-03
> 22 KSP preconditioned resid norm 1.497651066688e-04 true resid norm
> 7.045647741653e+04 ||r(i)||/||b|| 8.123618692570e-04
> 23 KSP preconditioned resid norm 1.067332245914e-04 true resid norm
> 4.317487154207e+04 ||r(i)||/||b|| 4.978054628463e-04
> 24 KSP preconditioned resid norm 8.206743871631e-05 true resid norm
> 3.328488127932e+04 ||r(i)||/||b|| 3.837740597534e-04
> 25 KSP preconditioned resid norm 6.446633932980e-05 true resid norm
> 2.816657573261e+04 ||r(i)||/||b|| 3.247600923538e-04
> 26 KSP preconditioned resid norm 5.068725017435e-05 true resid norm
> 2.427030232896e+04 ||r(i)||/||b|| 2.798361327495e-04
> 27 KSP preconditioned resid norm 4.056292508453e-05 true resid norm
> 1.963628903861e+04 ||r(i)||/||b|| 2.264060460243e-04
> 28 KSP preconditioned resid norm 3.278196251068e-05 true resid norm
> 1.710046122873e+04 ||r(i)||/||b|| 1.971679987179e-04
> 29 KSP preconditioned resid norm 2.796514916728e-05 true resid norm
> 1.500292999274e+04 ||r(i)||/||b|| 1.729835027259e-04
> 30 KSP preconditioned resid norm 2.469882695602e-05 true resid norm
> 1.317997814765e+04 ||r(i)||/||b|| 1.519649019847e-04
> 31 KSP preconditioned resid norm 2.175528107880e-05 true resid norm
> 1.158572445412e+04 ||r(i)||/||b|| 1.335831866616e-04
> 32 KSP preconditioned resid norm 1.912573933887e-05 true resid norm
> 1.001695718951e+04 ||r(i)||/||b|| 1.154953293880e-04
> 33 KSP preconditioned resid norm 1.647102125210e-05 true resid norm
> 8.271485921360e+03 ||r(i)||/||b|| 9.537007825249e-05
> 34 KSP preconditioned resid norm 1.337436641169e-05 true resid norm
> 6.611637805300e+03 ||r(i)||/||b|| 7.623206046211e-05
> 35 KSP preconditioned resid norm 9.896966695703e-06 true resid norm
> 4.752788536204e+03 ||r(i)||/||b|| 5.479956309238e-05
> 36 KSP preconditioned resid norm 6.766260764791e-06 true resid norm
> 3.239548441802e+03 ||r(i)||/||b|| 3.735193305468e-05
> 37 KSP preconditioned resid norm 4.835158711776e-06 true resid norm
> 2.113941262442e+03 ||r(i)||/||b|| 2.437370329068e-05
> 38 KSP preconditioned resid norm 3.598894380040e-06 true resid norm
> 1.653467554688e+03 ||r(i)||/||b|| 1.906445003688e-05
> 39 KSP preconditioned resid norm 2.522642742745e-06 true resid norm
> 1.344572919946e+03 ||r(i)||/||b|| 1.550290066507e-05
> 40 KSP preconditioned resid norm 1.750002168280e-06 true resid norm
> 1.015690774521e+03 ||r(i)||/||b|| 1.171089566825e-05
> 41 KSP preconditioned resid norm 1.371380245282e-06 true resid norm
> 8.480814540622e+02 ||r(i)||/||b|| 9.778363332462e-06
> 42 KSP preconditioned resid norm 1.174063380270e-06 true resid norm
> 7.575955225454e+02 ||r(i)||/||b|| 8.735062231359e-06
> 43 KSP preconditioned resid norm 1.022078284946e-06 true resid norm
> 6.758159410670e+02 ||r(i)||/||b|| 7.792145183661e-06
> 44 KSP preconditioned resid norm 8.861345665105e-07 true resid norm
> 5.913685641420e+02 ||r(i)||/||b|| 6.818468504268e-06
> 45 KSP preconditioned resid norm 7.574040382433e-07 true resid norm
> 4.958820201473e+02 ||r(i)||/||b|| 5.717510434653e-06
> 46 KSP preconditioned resid norm 6.331382122180e-07 true resid norm
> 3.988451175342e+02 ||r(i)||/||b|| 4.598676759110e-06
> 47 KSP preconditioned resid norm 5.210644796074e-07 true resid norm
> 3.077459761874e+02 ||r(i)||/||b|| 3.548305360116e-06
> 48 KSP preconditioned resid norm 4.285762531134e-07 true resid norm
> 2.383304155333e+02 ||r(i)||/||b|| 2.747945241696e-06
> 49 KSP preconditioned resid norm 3.365753654637e-07 true resid norm
> 1.802176480688e+02 ||r(i)||/||b|| 2.077906117741e-06
> 50 KSP preconditioned resid norm 2.556504175739e-07 true resid norm
> 1.322207275993e+02 ||r(i)||/||b|| 1.524502520785e-06
> 51 KSP preconditioned resid norm 1.929395464892e-07 true resid norm
> 1.007938656038e+02 ||r(i)||/||b|| 1.162151388686e-06
> 52 KSP preconditioned resid norm 1.518353128559e-07 true resid norm
> 7.979486270816e+01 ||r(i)||/||b|| 9.200332773308e-07
> 53 KSP preconditioned resid norm 1.206065500213e-07 true resid norm
> 6.580266981926e+01 ||r(i)||/||b|| 7.587035545427e-07
> 54 KSP preconditioned resid norm 9.426597887251e-08 true resid norm
> 5.333098459078e+01 ||r(i)||/||b|| 6.149052566928e-07
> 55 KSP preconditioned resid norm 7.613592162567e-08 true resid norm
> 4.265349984159e+01 ||r(i)||/||b|| 4.917940568733e-07
> 56 KSP preconditioned resid norm 6.268355987149e-08 true resid norm
> 3.467681120568e+01 ||r(i)||/||b|| 3.998229858184e-07
> 57 KSP preconditioned resid norm 5.012883291890e-08 true resid norm
> 2.749870530323e+01 ||r(i)||/||b|| 3.170595587716e-07
> 58 KSP preconditioned resid norm 3.875711489918e-08 true resid norm
> 2.037239239206e+01 ||r(i)||/||b|| 2.348933039472e-07
> 59 KSP preconditioned resid norm 2.803879910778e-08 true resid norm
> 1.495957468476e+01 ||r(i)||/||b|| 1.724836168342e-07
> 60 KSP preconditioned resid norm 1.925214804831e-08 true resid norm
> 1.036952152845e+01 ||r(i)||/||b|| 1.195603896339e-07
> 61 KSP preconditioned resid norm 1.316807047769e-08 true resid norm
> 7.239457203086e+00 ||r(i)||/||b|| 8.347080639779e-08
> 62 KSP preconditioned resid norm 9.095263534284e-09 true resid norm
> 5.546725364022e+00 ||r(i)||/||b|| 6.395363989508e-08
> 63 KSP preconditioned resid norm 6.520024982652e-09 true resid norm
> 4.395022539849e+00 ||r(i)||/||b|| 5.067452783356e-08
> 64 KSP preconditioned resid norm 5.077084953418e-09 true resid norm
> 3.613138054874e+00 ||r(i)||/||b|| 4.165941431885e-08
> 65 KSP preconditioned resid norm 4.181478103167e-09 true resid norm
> 3.038027368880e+00 ||r(i)||/||b|| 3.502839884610e-08
> 66 KSP preconditioned resid norm 3.474545560062e-09 true resid norm
> 2.484725611092e+00 ||r(i)||/||b|| 2.864883990842e-08
> 67 KSP preconditioned resid norm 2.726294735157e-09 true resid norm
> 1.845741997810e+00 ||r(i)||/||b|| 2.128137077650e-08
> 68 KSP preconditioned resid norm 2.081101207644e-09 true resid norm
> 1.271838867185e+00 ||r(i)||/||b|| 1.466427839462e-08
> 69 KSP preconditioned resid norm 1.574053677511e-09 true resid norm
> 8.732579381622e-01 ||r(i)||/||b|| 1.006864772411e-08
> 70 KSP preconditioned resid norm 1.202717674216e-09 true resid norm
> 5.849220507056e-01 ||r(i)||/||b|| 6.744140324696e-09
> 71 KSP preconditioned resid norm 9.075713740333e-10 true resid norm
> 4.120181311262e-01 ||r(i)||/||b|| 4.750561359898e-09
> 72 KSP preconditioned resid norm 6.365151508838e-10 true resid norm
> 3.065749731760e-01 ||r(i)||/||b|| 3.534803717256e-09
> 73 KSP preconditioned resid norm 4.005974496315e-10 true resid norm
> 2.122086214944e-01 ||r(i)||/||b|| 2.446761444097e-09
> 74 KSP preconditioned resid norm 2.374916890000e-10 true resid norm
> 1.567794082480e-01 ||r(i)||/||b|| 1.807663650177e-09
> 75 KSP preconditioned resid norm 1.481096397633e-10 true resid norm
> 1.235242757193e-01 ||r(i)||/||b|| 1.424232592963e-09
> 76 KSP preconditioned resid norm 1.085014154415e-10 true resid norm
> 1.047268461651e-01 ||r(i)||/||b|| 1.207498581132e-09
> 77 KSP preconditioned resid norm 8.764582618532e-11 true resid norm
> 8.962364559579e-02 ||r(i)||/||b|| 1.033358960531e-09
> 78 KSP preconditioned resid norm 7.109092680274e-11 true resid norm
> 7.176047852904e-02 ||r(i)||/||b|| 8.273969777399e-10
> 79 KSP preconditioned resid norm 5.460763497752e-11 true resid norm
> 5.069849340150e-02 ||r(i)||/||b|| 5.845526824266e-10
> 80 KSP preconditioned resid norm 3.799942459039e-11 true resid norm
> 3.044234442091e-02 ||r(i)||/||b|| 3.509996628435e-10
> 81 KSP preconditioned resid norm 2.481109284531e-11 true resid norm
> 1.726059230919e-02 ||r(i)||/||b|| 1.990143070861e-10
> 82 KSP preconditioned resid norm 1.569622532234e-11 true resid norm
> 1.070220060596e-02 ||r(i)||/||b|| 1.233961731867e-10
> 83 KSP preconditioned resid norm 1.022582071414e-11 true resid norm
> 7.402265790954e-03 ||r(i)||/||b|| 8.534798637643e-11
> 84 KSP preconditioned resid norm 7.284827374238e-12 true resid norm
> 5.658340974708e-03 ||r(i)||/||b|| 6.524056580253e-11
> 85 KSP preconditioned resid norm 5.402886839508e-12 true resid norm
> 4.464802757767e-03 ||r(i)||/||b|| 5.147909244343e-11
> 86 KSP preconditioned resid norm 3.933784995327e-12 true resid norm
> 3.350654653931e-03 ||r(i)||/||b|| 3.863298560628e-11
> 87 KSP preconditioned resid norm 2.792049995877e-12 true resid norm
> 2.402140873006e-03 ||r(i)||/||b|| 2.769663942007e-11
> 88 KSP preconditioned resid norm 2.058524741199e-12 true resid norm
> 1.747330249674e-03 ||r(i)||/||b|| 2.014668515774e-11
> 89 KSP preconditioned resid norm 1.568241303093e-12 true resid norm
> 1.266336540932e-03 ||r(i)||/||b|| 1.460083667564e-11
> 90 KSP preconditioned resid norm 1.164779378453e-12 true resid norm
> 8.484550691359e-04 ||r(i)||/||b|| 9.782671107287e-12
> 91 KSP preconditioned resid norm 7.995560038101e-13 true resid norm
> 5.065061038629e-04 ||r(i)||/||b|| 5.840005921551e-12
> Linear solve converged due to CONVERGED_RTOL iterations 91
> KSP Object: 8 MPI processes
> type: gmres
> GMRES: restart=300, using Modified Gram-Schmidt Orthogonalization
> GMRES: happy breakdown tolerance 1e-30
> maximum iterations=300, initial guess is zero
> tolerances: relative=1e-12, absolute=1e-20, divergence=10000
> left preconditioning
> using PRECONDITIONED norm type for convergence test
> PC Object: 8 MPI processes
> type: fieldsplit
> FieldSplit with MULTIPLICATIVE composition: total splits = 2
> Solver info for each split is in the following KSP objects:
> Split number 0 Defined by IS
> KSP Object: (fieldsplit_u_) 8 MPI processes
> type: preonly
> maximum iterations=10000, initial guess is zero
> tolerances: relative=1e-05, absolute=1e-50, divergence=10000
> left preconditioning
> using NONE norm type for convergence test
> PC Object: (fieldsplit_u_) 8 MPI processes
> type: hypre
> HYPRE BoomerAMG preconditioning
> HYPRE BoomerAMG: Cycle type V
> HYPRE BoomerAMG: Maximum number of levels 25
> HYPRE BoomerAMG: Maximum number of iterations PER hypre call 1
> HYPRE BoomerAMG: Convergence tolerance PER hypre call 0
> HYPRE BoomerAMG: Threshold for strong coupling 0.6
> HYPRE BoomerAMG: Interpolation truncation factor 0
> HYPRE BoomerAMG: Interpolation: max elements per row 0
> HYPRE BoomerAMG: Number of levels of aggressive coarsening 0
> HYPRE BoomerAMG: Number of paths for aggressive coarsening 1
> HYPRE BoomerAMG: Maximum row sums 0.9
> HYPRE BoomerAMG: Sweeps down 1
> HYPRE BoomerAMG: Sweeps up 1
> HYPRE BoomerAMG: Sweeps on coarse 1
> HYPRE BoomerAMG: Relax down symmetric-SOR/Jacobi
> HYPRE BoomerAMG: Relax up symmetric-SOR/Jacobi
> HYPRE BoomerAMG: Relax on coarse Gaussian-elimination
> HYPRE BoomerAMG: Relax weight (all) 1
> HYPRE BoomerAMG: Outer relax weight (all) 1
> HYPRE BoomerAMG: Using CF-relaxation
> HYPRE BoomerAMG: Measure type local
> HYPRE BoomerAMG: Coarsen type PMIS
> HYPRE BoomerAMG: Interpolation type classical
> linear system matrix = precond matrix:
> Mat Object: (fieldsplit_u_) 8 MPI processes
> type: mpiaij
> rows=438420, cols=438420, bs=3
> total: nonzeros=7.95766e+07, allocated nonzeros=7.95766e+07
> total number of mallocs used during MatSetValues calls =0
> using I-node (on process 0) routines: found 17349 nodes, limit used
> is 5
> Split number 1 Defined by IS
> KSP Object: (fieldsplit_wp_) 8 MPI processes
> type: preonly
> maximum iterations=10000, initial guess is zero
> tolerances: relative=1e-05, absolute=1e-50, divergence=10000
> left preconditioning
> using NONE norm type for convergence test
> PC Object: (fieldsplit_wp_) 8 MPI processes
> type: hypre
> HYPRE BoomerAMG preconditioning
> HYPRE BoomerAMG: Cycle type V
> HYPRE BoomerAMG: Maximum number of levels 25
> HYPRE BoomerAMG: Maximum number of iterations PER hypre call 1
> HYPRE BoomerAMG: Convergence tolerance PER hypre call 0
> HYPRE BoomerAMG: Threshold for strong coupling 0.6
> HYPRE BoomerAMG: Interpolation truncation factor 0
> HYPRE BoomerAMG: Interpolation: max elements per row 0
> HYPRE BoomerAMG: Number of levels of aggressive coarsening 0
> HYPRE BoomerAMG: Number of paths for aggressive coarsening 1
> HYPRE BoomerAMG: Maximum row sums 0.9
> HYPRE BoomerAMG: Sweeps down 1
> HYPRE BoomerAMG: Sweeps up 1
> HYPRE BoomerAMG: Sweeps on coarse 1
> HYPRE BoomerAMG: Relax down symmetric-SOR/Jacobi
> HYPRE BoomerAMG: Relax up symmetric-SOR/Jacobi
> HYPRE BoomerAMG: Relax on coarse Gaussian-elimination
> HYPRE BoomerAMG: Relax weight (all) 1
> HYPRE BoomerAMG: Outer relax weight (all) 1
> HYPRE BoomerAMG: Using CF-relaxation
> HYPRE BoomerAMG: Measure type local
> HYPRE BoomerAMG: Coarsen type PMIS
> HYPRE BoomerAMG: Interpolation type classical
> linear system matrix = precond matrix:
> Mat Object: (fieldsplit_wp_) 8 MPI processes
> type: mpiaij
> rows=146140, cols=146140
> total: nonzeros=596012, allocated nonzeros=596012
> total number of mallocs used during MatSetValues calls =0
> not using I-node (on process 0) routines
> linear system matrix = precond matrix:
> Mat Object: 8 MPI processes
> type: mpiaij
> rows=584560, cols=584560, bs=4
> total: nonzeros=9.29667e+07, allocated nonzeros=9.29667e+07
> total number of mallocs used during MatSetValues calls =0
> using I-node (on process 0) routines: found 32431 nodes, limit used is 5
> KSPSolve completed
>
>
> Giang
>
> On Wed, Jul 13, 2016 at 5:43 AM, Barry Smith <[email protected]> wrote:
>
> It is not uncommon for an iterative linear solver to work fine for some
> time steps but then start to perform poorly at a later timestep because the
> physics (mathematically the conditioning or eigenstructure of the Jacobian)
> changes over time; perhaps becomes singular. Another possibility is the
> trajectory of the solution is very sensitive to the solution of the nonlinear
> problem at each time step so that an iterative linear solver and a direct
> linear solver result in very difficult physical solutions after many time
> steps. In other words after many time-steps the computed solutions can be
> very different and if the computed solution for the iterative linear solver
> is eventually "non-physical" or ill-conditioned the nonlinear solver could
> break down.
>
> Please run with the iterative solver (that eventually breaks) with the
> option -ksp_monitor_true_solution -ksp_converged_reason and and send ALL the
> output (it will be very large, don't worry about it). Then we can see if the
> linear solver is breaking down. Note that by default PETSc linear solvers do
> not generate an error that stops the program if the linear solve fails, hence
> your NR code should call KSPGetConvergedReason() after EVERY linear solve and
> if the reason is negative your code needs to do something different since the
> linear solve failed and your code should not just keep on running NR.
>
> Barry
>
>
> > On Jul 12, 2016, at 9:52 AM, Matthew Knepley <[email protected]> wrote:
> >
> > On Tue, Jul 12, 2016 at 8:44 AM, Hoang Giang Bui <[email protected]> wrote:
> > Hi Matt
> >
> > 1) In the log you sent, the linear solver converges due to the Relative
> > Tolerance, 1.0e-9, not the breakdown tolerance 1e-30. Change rtol will
> > affect the convergence.
> >
> > Sorry i got it wrong in the previous email, the ksp_rtol 1.0e-12 DOES
> > affect the convergence, and it took more iterations. But the simulation
> > still failed at a definite time step.
> >
> > 2) What do you mean -fieldsplit_wp_ksp_rtol 1.0e-8 does not work? ALWAYS
> > send the view output.
> >
> > In the log file I sent previously, the line
> >
> > KSP Object: (fieldsplit_wp_) 8 MPI processes
> > type: preonly
> > maximum iterations=10000, initial guess is zero
> > tolerances: relative=1e-05, absolute=1e-50, divergence=10000
> > left preconditioning
> > using NONE norm type for convergence test
> >
> > impressed me that the rtol for fieldsplit_wp is still 1.0e-5
> >
> > KSP "preonly" does no iterations, so it does not read the tolerance. If you
> > want to lower the tolerance,
> > choose a solver like GMRES
> >
> > -fieldsplit_wp_ksp_type gmres -fieldsplit_wp_ksp_rtol 1e-8
> >
> > 3) I can't tell you anything about Newton convergence if you do not send
> > the output, -snes_monitor -snes_view
> >
> > I did not yet use SNES, instead using my NR iterator so I have no view for
> > SNES.
> >
> > It is hard to debug an iteration which we did not code. It could be you
> > have a bug. If not, then very small changes in
> > the iterates are making a difference, which means your Jacobians are close
> > to singular. A problem reformulation would
> > probably help more than solver tweaking.
> >
> > Thanks,
> >
> > Matt
> >
> > 4) If there is a difference between LU and an iterative solver with
> > residual 1e-9, then your system is very ill-conditioned.
> > Yes it is ill-conditioned
> >
> >
> >
> >
> >
> >
> >
> > Giang
> >
> > On Tue, Jul 12, 2016 at 2:49 PM, Matthew Knepley <[email protected]> wrote:
> > On Tue, Jul 12, 2016 at 7:42 AM, Hoang Giang Bui <[email protected]> wrote:
> > Hello
> >
> > I encountered different convergence behaviour of Newton Raphson when using
> > different solver settings with PETSc
> >
> > For the first solver configuration, I used direct solver
> > -ksp_type preonly
> > -pc_type lu
> > -pc_factor_mat_solver_package mumps
> > -mat_mumps_icntl_1 6
> > -mat_mumps_icntl_4 3
> > -mat_mumps_icntl_7 4
> > -mat_mumps_icntl_14 40
> > -mat_mumps_icntl_23 0
> >
> > The simulation can run completely and the NR typically converged after 6/7
> > iterations. Of course, it's very slow. For the second solver configuration:
> > -ksp_type gmres
> > -ksp_max_it 300
> > -ksp_gmres_restart 300
> > -ksp_gmres_modifiedgramschmidt
> > -pc_view
> > -pc_fieldsplit_type multiplicative
> > -fieldsplit_u_pc_type hypre
> > -fieldsplit_u_pc_hypre_type boomeramg
> > -fieldsplit_u_pc_hypre_boomeramg_coarsen_type PMIS
> > -fieldsplit_u_pc_hypre_boomeramg_strong_threshold 0.6
> > -fieldsplit_u_pc_hypre_boomeramg_max_levels 25
> > -fieldsplit_wp_ksp_rtol 1.0e-8
> > -fieldsplit_wp_pc_type hypre
> > -fieldsplit_wp_pc_hypre_type boomeramg
> > -fieldsplit_wp_pc_hypre_boomeramg_coarsen_type PMIS
> > -fieldsplit_wp_pc_hypre_boomeramg_strong_threshold 0.6
> > -fieldsplit_wp_pc_hypre_boomeramg_max_levels 25
> >
> > The solver runs much faster, but the NR does not converge in 30 iterations
> > after some time steps. I thought setting the solver tolerance -ksp_rtol
> > 1.0e-12 but it doesn't help much because GMRES already terminate with
> > tolerance 1e-30 (see sample log file). Can we set the tolerance of the
> > sub-ksp of the Fieldsplit? I tried -fieldsplit_wp_ksp_rtol 1.0e-8 but it
> > doesn't work.
> >
> > 1) In the log you sent, the linear solver converges due to the Relative
> > Tolerance, 1.0e-9, not the breakdown tolerance 1e-30. Change rtol will
> > affect the convergence.
> >
> > 2) What do you mean -fieldsplit_wp_ksp_rtol 1.0e-8 does not work? ALWAYS
> > send the view output.
> >
> > 3) I can't tell you anything about Newton convergence if you do not send
> > the output, -snes_monitor -snes_view
> >
> > 4) If there is a difference between LU and an iterative solver with
> > residual 1e-9, then your system is very ill-conditioned.
> >
> > Thanks,
> >
> > Matt
> >
> > Sorry this problem is run with many time steps and is quite big so I cannot
> > reproduce in a simple test case.
> >
> > Giang
> >
> >
> >
> >
> > --
> > 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
> >
> >
> >
> >
> > --
> > 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
>
>
>
>
>
> --
> 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
