<div dir="ltr">It took a while, here I send you the output<div><br></div><div><div> 0 KSP preconditioned resid norm 3.129073545457e+05 true resid norm 9.015150492169e+06 ||r(i)||/||b|| 1.000000000000e+00</div><div> 1 KSP preconditioned resid norm 7.442444222843e-01 true resid norm 1.003356247696e+02 ||r(i)||/||b|| 1.112966720375e-05</div><div> 2 KSP preconditioned resid norm 3.267453132529e-07 true resid norm 3.216722968300e+01 ||r(i)||/||b|| 3.568130084011e-06</div><div> 3 KSP preconditioned resid norm 1.155046883816e-11 true resid norm 3.234460376820e+01 ||r(i)||/||b|| 3.587805194854e-06</div><div>Linear solve converged due to CONVERGED_ATOL iterations 3</div><div>KSP Object: 4 MPI processes</div><div> type: gmres</div><div> GMRES: restart=1000, using Modified Gram-Schmidt Orthogonalization</div><div> GMRES: happy breakdown tolerance 1e-30</div><div> maximum iterations=1000, initial guess is zero</div><div> tolerances: relative=1e-20, absolute=1e-09, divergence=10000</div><div> left preconditioning</div><div> using PRECONDITIONED norm type for convergence test</div><div>PC Object: 4 MPI processes</div><div> type: lu</div><div> LU: out-of-place factorization</div><div> tolerance for zero pivot 2.22045e-14</div><div> matrix ordering: natural</div><div> factor fill ratio given 0, needed 0</div><div> Factored matrix follows:</div><div> Mat Object: 4 MPI processes</div><div> type: mpiaij</div><div> rows=973051, cols=973051</div><div> package used to perform factorization: pastix</div><div> Error : 3.24786e-14</div><div> total: nonzeros=0, allocated nonzeros=0</div><div> total number of mallocs used during MatSetValues calls =0</div><div> PaStiX run parameters:</div><div> Matrix type : Unsymmetric</div><div> Level of printing (0,1,2): 0</div><div> Number of refinements iterations : 3</div><div> Error : 3.24786e-14</div><div> linear system matrix = precond matrix:</div><div> Mat Object: 4 MPI processes</div><div> type: mpiaij</div><div> rows=973051, cols=973051</div><div> Error : 3.24786e-14</div><div> total: nonzeros=9.90037e+07, allocated nonzeros=9.90037e+07</div><div> total number of mallocs used during MatSetValues calls =0</div><div> using I-node (on process 0) routines: found 78749 nodes, limit used is 5</div><div> Error : 3.24786e-14</div><div><br></div><div>It doesn't do as you said. Something is not right here. I will look in depth.</div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature"><div dir="ltr">Giang</div></div></div>
<br><div class="gmail_quote">On Mon, Apr 24, 2017 at 8:21 PM, Barry Smith <span dir="ltr"><<a href="mailto:bsmith@mcs.anl.gov" target="_blank">bsmith@mcs.anl.gov</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><span class="gmail-"><br>
> On Apr 24, 2017, at 12:47 PM, Hoang Giang Bui <<a href="mailto:hgbk2008@gmail.com">hgbk2008@gmail.com</a>> wrote:<br>
><br>
> Good catch. I get this for the very first step, maybe at that time the rhs_w is zero.<br>
<br>
</span> With the multiplicative composition the right hand side of the second solve is the initial right hand side of the second solve minus A_10*x where x is the solution to the first sub solve and A_10 is the lower left block of the outer matrix. So unless both the initial right hand side has a zero for the second block and A_10 is identically zero the right hand side for the second sub solve should not be zero. Is A_10 == 0?<br>
<span class="gmail-"><br>
<br>
> In the later step, it shows 2 step convergence<br>
><br>
> Residual norms for fieldsplit_u_ solve.<br>
> 0 KSP Residual norm 3.165886479830e+04<br>
> 1 KSP Residual norm 2.905922877684e-01<br>
> Residual norms for fieldsplit_wp_ solve.<br>
> 0 KSP Residual norm 2.397669419027e-01<br>
> 1 KSP Residual norm 0.000000000000e+00<br>
> 0 KSP preconditioned resid norm 3.165886479920e+04 true resid norm 7.963616922323e+05 ||r(i)||/||b|| 1.000000000000e+00<br>
> Residual norms for fieldsplit_u_ solve.<br>
> 0 KSP Residual norm 9.999891813771e-01<br>
> 1 KSP Residual norm 1.512000395579e-05<br>
> Residual norms for fieldsplit_wp_ solve.<br>
> 0 KSP Residual norm 8.192702188243e-06<br>
> 1 KSP Residual norm 0.000000000000e+00<br>
> 1 KSP preconditioned resid norm 5.252183822848e-02 true resid norm 7.135927677844e+04 ||r(i)||/||b|| 8.960661653427e-02<br>
<br>
</span> The outer residual norms are still wonky, the preconditioned residual norm goes from 3.165886479920e+04 to 5.252183822848e-02 which is a huge drop but the 7.963616922323e+05 drops very much less 7.135927677844e+04. This is not normal.<br>
<br>
What if you just use -pc_type lu for the entire system (no fieldsplit), does the true residual drop to almost zero in the first iteration (as it should?). Send the output.<br>
<div class="gmail-HOEnZb"><div class="gmail-h5"><br>
<br>
<br>
> Residual norms for fieldsplit_u_ solve.<br>
> 0 KSP Residual norm 6.946213936597e-01<br>
> 1 KSP Residual norm 1.195514007343e-05<br>
> Residual norms for fieldsplit_wp_ solve.<br>
> 0 KSP Residual norm 1.025694497535e+00<br>
> 1 KSP Residual norm 0.000000000000e+00<br>
> 2 KSP preconditioned resid norm 8.785709535405e-03 true resid norm 1.419341799277e+04 ||r(i)||/||b|| 1.782282866091e-02<br>
> Residual norms for fieldsplit_u_ solve.<br>
> 0 KSP Residual norm 7.255149996405e-01<br>
> 1 KSP Residual norm 6.583512434218e-06<br>
> Residual norms for fieldsplit_wp_ solve.<br>
> 0 KSP Residual norm 1.015229700337e+00<br>
> 1 KSP Residual norm 0.000000000000e+00<br>
> 3 KSP preconditioned resid norm 7.110407712709e-04 true resid norm 5.284940654154e+02 ||r(i)||/||b|| 6.636357205153e-04<br>
> Residual norms for fieldsplit_u_ solve.<br>
> 0 KSP Residual norm 3.512243341400e-01<br>
> 1 KSP Residual norm 2.032490351200e-06<br>
> Residual norms for fieldsplit_wp_ solve.<br>
> 0 KSP Residual norm 1.282327290982e+00<br>
> 1 KSP Residual norm 0.000000000000e+00<br>
> 4 KSP preconditioned resid norm 3.482036620521e-05 true resid norm 4.291231924307e+01 ||r(i)||/||b|| 5.388546393133e-05<br>
> Residual norms for fieldsplit_u_ solve.<br>
> 0 KSP Residual norm 3.423609338053e-01<br>
> 1 KSP Residual norm 4.213703301972e-07<br>
> Residual norms for fieldsplit_wp_ solve.<br>
> 0 KSP Residual norm 1.157384757538e+00<br>
> 1 KSP Residual norm 0.000000000000e+00<br>
> 5 KSP preconditioned resid norm 1.203470314534e-06 true resid norm 4.544956156267e+00 ||r(i)||/||b|| 5.707150658550e-06<br>
> Residual norms for fieldsplit_u_ solve.<br>
> 0 KSP Residual norm 3.838596289995e-01<br>
> 1 KSP Residual norm 9.927864176103e-08<br>
> Residual norms for fieldsplit_wp_ solve.<br>
> 0 KSP Residual norm 1.066298905618e+00<br>
> 1 KSP Residual norm 0.000000000000e+00<br>
> 6 KSP preconditioned resid norm 3.331619244266e-08 true resid norm 2.821511729024e+00 ||r(i)||/||b|| 3.543002829675e-06<br>
> Residual norms for fieldsplit_u_ solve.<br>
> 0 KSP Residual norm 4.624964188094e-01<br>
> 1 KSP Residual norm 6.418229775372e-08<br>
> Residual norms for fieldsplit_wp_ solve.<br>
> 0 KSP Residual norm 9.800784311614e-01<br>
> 1 KSP Residual norm 0.000000000000e+00<br>
> 7 KSP preconditioned resid norm 8.788046233297e-10 true resid norm 2.849209671705e+00 ||r(i)||/||b|| 3.577783436215e-06<br>
> Linear solve converged due to CONVERGED_ATOL iterations 7<br>
><br>
> The outer operator is an explicit matrix.<br>
><br>
> Giang<br>
><br>
> On Mon, Apr 24, 2017 at 7:32 PM, Barry Smith <<a href="mailto:bsmith@mcs.anl.gov">bsmith@mcs.anl.gov</a>> wrote:<br>
><br>
> > On Apr 24, 2017, at 3:16 AM, Hoang Giang Bui <<a href="mailto:hgbk2008@gmail.com">hgbk2008@gmail.com</a>> wrote:<br>
> ><br>
> > Thanks Barry, trying with -fieldsplit_u_type lu gives better convergence. I still used 4 procs though, probably with 1 proc it should also be the same.<br>
> ><br>
> > The u block used a Nitsche-type operator to connect two non-matching domains. I don't think it will leave some rigid body motion leads to not sufficient constraints. Maybe you have other idea?<br>
> ><br>
> > Residual norms for fieldsplit_u_ solve.<br>
> > 0 KSP Residual norm 3.129067184300e+05<br>
> > 1 KSP Residual norm 5.906261468196e-01<br>
> > Residual norms for fieldsplit_wp_ solve.<br>
> > 0 KSP Residual norm 0.000000000000e+00<br>
><br>
> ^^^^ something is wrong here. The sub solve should not be starting with a 0 residual (this means the right hand side for this sub solve is zero which it should not be).<br>
><br>
> > FieldSplit with MULTIPLICATIVE composition: total splits = 2<br>
><br>
><br>
> How are you providing the outer operator? As an explicit matrix or with some shell matrix?<br>
><br>
><br>
><br>
> > 0 KSP preconditioned resid norm 3.129067184300e+05 true resid norm 9.015150492169e+06 ||r(i)||/||b|| 1.000000000000e+00<br>
> > Residual norms for fieldsplit_u_ solve.<br>
> > 0 KSP Residual norm 9.999955993437e-01<br>
> > 1 KSP Residual norm 4.019774691831e-06<br>
> > Residual norms for fieldsplit_wp_ solve.<br>
> > 0 KSP Residual norm 0.000000000000e+00<br>
> > 1 KSP preconditioned resid norm 5.003913641475e-01 true resid norm 4.692996324114e+01 ||r(i)||/||b|| 5.205677185522e-06<br>
> > Residual norms for fieldsplit_u_ solve.<br>
> > 0 KSP Residual norm 1.000012180204e+00<br>
> > 1 KSP Residual norm 1.017367950422e-05<br>
> > Residual norms for fieldsplit_wp_ solve.<br>
> > 0 KSP Residual norm 0.000000000000e+00<br>
> > 2 KSP preconditioned resid norm 2.330910333756e-07 true resid norm 3.474855463983e+01 ||r(i)||/||b|| 3.854461960453e-06<br>
> > Residual norms for fieldsplit_u_ solve.<br>
> > 0 KSP Residual norm 1.000004200085e+00<br>
> > 1 KSP Residual norm 6.231613102458e-06<br>
> > Residual norms for fieldsplit_wp_ solve.<br>
> > 0 KSP Residual norm 0.000000000000e+00<br>
> > 3 KSP preconditioned resid norm 8.671259838389e-11 true resid norm 3.545103468011e+01 ||r(i)||/||b|| 3.932384125024e-06<br>
> > Linear solve converged due to CONVERGED_ATOL iterations 3<br>
> > KSP Object: 4 MPI processes<br>
> > type: gmres<br>
> > GMRES: restart=1000, using Modified Gram-Schmidt Orthogonalization<br>
> > GMRES: happy breakdown tolerance 1e-30<br>
> > maximum iterations=1000, initial guess is zero<br>
> > tolerances: relative=1e-20, absolute=1e-09, divergence=10000<br>
> > left preconditioning<br>
> > using PRECONDITIONED norm type for convergence test<br>
> > PC Object: 4 MPI processes<br>
> > type: fieldsplit<br>
> > FieldSplit with MULTIPLICATIVE composition: total splits = 2<br>
> > Solver info for each split is in the following KSP objects:<br>
> > Split number 0 Defined by IS<br>
> > KSP Object: (fieldsplit_u_) 4 MPI processes<br>
> > type: richardson<br>
> > Richardson: damping factor=1<br>
> > maximum iterations=1, initial guess is zero<br>
> > tolerances: relative=1e-05, absolute=1e-50, divergence=10000<br>
> > left preconditioning<br>
> > using PRECONDITIONED norm type for convergence test<br>
> > PC Object: (fieldsplit_u_) 4 MPI processes<br>
> > type: lu<br>
> > LU: out-of-place factorization<br>
> > tolerance for zero pivot 2.22045e-14<br>
> > matrix ordering: natural<br>
> > factor fill ratio given 0, needed 0<br>
> > Factored matrix follows:<br>
> > Mat Object: 4 MPI processes<br>
> > type: mpiaij<br>
> > rows=938910, cols=938910<br>
> > package used to perform factorization: pastix<br>
> > total: nonzeros=0, allocated nonzeros=0<br>
> > Error : 3.36878e-14<br>
> > total number of mallocs used during MatSetValues calls =0<br>
> > PaStiX run parameters:<br>
> > Matrix type : Unsymmetric<br>
> > Level of printing (0,1,2): 0<br>
> > Number of refinements iterations : 3<br>
> > Error : 3.36878e-14<br>
> > linear system matrix = precond matrix:<br>
> > Mat Object: (fieldsplit_u_) 4 MPI processes<br>
> > type: mpiaij<br>
> > rows=938910, cols=938910, bs=3<br>
> > Error : 3.36878e-14<br>
> > Error : 3.36878e-14<br>
> > total: nonzeros=8.60906e+07, allocated nonzeros=8.60906e+07<br>
> > total number of mallocs used during MatSetValues calls =0<br>
> > using I-node (on process 0) routines: found 78749 nodes, limit used is 5<br>
> > Split number 1 Defined by IS<br>
> > KSP Object: (fieldsplit_wp_) 4 MPI processes<br>
> > type: richardson<br>
> > Richardson: damping factor=1<br>
> > maximum iterations=1, initial guess is zero<br>
> > tolerances: relative=1e-05, absolute=1e-50, divergence=10000<br>
> > left preconditioning<br>
> > using PRECONDITIONED norm type for convergence test<br>
> > PC Object: (fieldsplit_wp_) 4 MPI processes<br>
> > type: lu<br>
> > LU: out-of-place factorization<br>
> > tolerance for zero pivot 2.22045e-14<br>
> > matrix ordering: natural<br>
> > factor fill ratio given 0, needed 0<br>
> > Factored matrix follows:<br>
> > Mat Object: 4 MPI processes<br>
> > type: mpiaij<br>
> > rows=34141, cols=34141<br>
> > package used to perform factorization: pastix<br>
> > Error : -nan<br>
> > Error : -nan<br>
> > Error : -nan<br>
> > total: nonzeros=0, allocated nonzeros=0<br>
> > total number of mallocs used during MatSetValues calls =0<br>
> > PaStiX run parameters:<br>
> > Matrix type : Symmetric<br>
> > Level of printing (0,1,2): 0<br>
> > Number of refinements iterations : 0<br>
> > Error : -nan<br>
> > linear system matrix = precond matrix:<br>
> > Mat Object: (fieldsplit_wp_) 4 MPI processes<br>
> > type: mpiaij<br>
> > rows=34141, cols=34141<br>
> > total: nonzeros=485655, allocated nonzeros=485655<br>
> > total number of mallocs used during MatSetValues calls =0<br>
> > not using I-node (on process 0) routines<br>
> > linear system matrix = precond matrix:<br>
> > Mat Object: 4 MPI processes<br>
> > type: mpiaij<br>
> > rows=973051, cols=973051<br>
> > total: nonzeros=9.90037e+07, allocated nonzeros=9.90037e+07<br>
> > total number of mallocs used during MatSetValues calls =0<br>
> > using I-node (on process 0) routines: found 78749 nodes, limit used is 5<br>
> ><br>
> ><br>
> ><br>
> > Giang<br>
> ><br>
> > On Sun, Apr 23, 2017 at 10:19 PM, Barry Smith <<a href="mailto:bsmith@mcs.anl.gov">bsmith@mcs.anl.gov</a>> wrote:<br>
> ><br>
> > > On Apr 23, 2017, at 2:42 PM, Hoang Giang Bui <<a href="mailto:hgbk2008@gmail.com">hgbk2008@gmail.com</a>> wrote:<br>
> > ><br>
> > > Dear Matt/Barry<br>
> > ><br>
> > > With your options, it results in<br>
> > ><br>
> > > 0 KSP preconditioned resid norm 1.106709687386e+31 true resid norm 9.015150491938e+06 ||r(i)||/||b|| 1.000000000000e+00<br>
> > > Residual norms for fieldsplit_u_ solve.<br>
> > > 0 KSP Residual norm 2.407308987203e+36<br>
> > > 1 KSP Residual norm 5.797185652683e+72<br>
> ><br>
> > It looks like Matt is right, hypre is seemly producing useless garbage.<br>
> ><br>
> > First how do things run on one process. If you have similar problems then debug on one process (debugging any kind of problem is always far easy on one process).<br>
> ><br>
> > First run with -fieldsplit_u_type lu (instead of using hypre) to see if that works or also produces something bad.<br>
> ><br>
> > What is the operator and the boundary conditions for u? It could be singular.<br>
> ><br>
> ><br>
> ><br>
> ><br>
> ><br>
> ><br>
> > > Residual norms for fieldsplit_wp_ solve.<br>
> > > 0 KSP Residual norm 0.000000000000e+00<br>
> > > ...<br>
> > > 999 KSP preconditioned resid norm 2.920157329174e+12 true resid norm 9.015683504616e+06 ||r(i)||/||b|| 1.000059124102e+00<br>
> > > Residual norms for fieldsplit_u_ solve.<br>
> > > 0 KSP Residual norm 1.533726746719e+36<br>
> > > 1 KSP Residual norm 3.692757392261e+72<br>
> > > Residual norms for fieldsplit_wp_ solve.<br>
> > > 0 KSP Residual norm 0.000000000000e+00<br>
> > ><br>
> > > Do you suggest that the pastix solver for the "wp" block encounters small pivot? In addition, seem like the "u" block is also singular.<br>
> > ><br>
> > > Giang<br>
> > ><br>
> > > On Sun, Apr 23, 2017 at 7:39 PM, Barry Smith <<a href="mailto:bsmith@mcs.anl.gov">bsmith@mcs.anl.gov</a>> wrote:<br>
> > ><br>
> > > Huge preconditioned norms but normal unpreconditioned norms almost always come from a very small pivot in an LU or ILU factorization.<br>
> > ><br>
> > > The first thing to do is monitor the two sub solves. Run with the additional options -fieldsplit_u_ksp_type richardson -fieldsplit_u_ksp_monitor -fieldsplit_u_ksp_max_it 1 -fieldsplit_wp_ksp_type richardson -fieldsplit_wp_ksp_monitor -fieldsplit_wp_ksp_max_it 1<br>
> > ><br>
> > > > On Apr 23, 2017, at 12:22 PM, Hoang Giang Bui <<a href="mailto:hgbk2008@gmail.com">hgbk2008@gmail.com</a>> wrote:<br>
> > > ><br>
> > > > Hello<br>
> > > ><br>
> > > > I encountered a strange convergence behavior that I have trouble to understand<br>
> > > ><br>
> > > > KSPSetFromOptions completed<br>
> > > > 0 KSP preconditioned resid norm 1.106709687386e+31 true resid norm 9.015150491938e+06 ||r(i)||/||b|| 1.000000000000e+00<br>
> > > > 1 KSP preconditioned resid norm 2.933141742664e+29 true resid norm 9.015152282123e+06 ||r(i)||/||b|| 1.000000198575e+00<br>
> > > > 2 KSP preconditioned resid norm 9.686409637174e+16 true resid norm 9.015354521944e+06 ||r(i)||/||b|| 1.000022631902e+00<br>
> > > > 3 KSP preconditioned resid norm 4.219243615809e+15 true resid norm 9.017157702420e+06 ||r(i)||/||b|| 1.000222648583e+00<br>
> > > > .....<br>
> > > > 999 KSP preconditioned resid norm 3.043754298076e+12 true resid norm 9.015425041089e+06 ||r(i)||/||b|| 1.000030454195e+00<br>
> > > > 1000 KSP preconditioned resid norm 3.043000287819e+12 true resid norm 9.015424313455e+06 ||r(i)||/||b|| 1.000030373483e+00<br>
> > > > Linear solve did not converge due to DIVERGED_ITS iterations 1000<br>
> > > > KSP Object: 4 MPI processes<br>
> > > > type: gmres<br>
> > > > GMRES: restart=1000, using Modified Gram-Schmidt Orthogonalization<br>
> > > > GMRES: happy breakdown tolerance 1e-30<br>
> > > > maximum iterations=1000, initial guess is zero<br>
> > > > tolerances: relative=1e-20, absolute=1e-09, divergence=10000<br>
> > > > left preconditioning<br>
> > > > using PRECONDITIONED norm type for convergence test<br>
> > > > PC Object: 4 MPI processes<br>
> > > > type: fieldsplit<br>
> > > > FieldSplit with MULTIPLICATIVE composition: total splits = 2<br>
> > > > Solver info for each split is in the following KSP objects:<br>
> > > > Split number 0 Defined by IS<br>
> > > > KSP Object: (fieldsplit_u_) 4 MPI processes<br>
> > > > type: preonly<br>
> > > > maximum iterations=10000, initial guess is zero<br>
> > > > tolerances: relative=1e-05, absolute=1e-50, divergence=10000<br>
> > > > left preconditioning<br>
> > > > using NONE norm type for convergence test<br>
> > > > PC Object: (fieldsplit_u_) 4 MPI processes<br>
> > > > type: hypre<br>
> > > > HYPRE BoomerAMG preconditioning<br>
> > > > HYPRE BoomerAMG: Cycle type V<br>
> > > > HYPRE BoomerAMG: Maximum number of levels 25<br>
> > > > HYPRE BoomerAMG: Maximum number of iterations PER hypre call 1<br>
> > > > HYPRE BoomerAMG: Convergence tolerance PER hypre call 0<br>
> > > > HYPRE BoomerAMG: Threshold for strong coupling 0.6<br>
> > > > HYPRE BoomerAMG: Interpolation truncation factor 0<br>
> > > > HYPRE BoomerAMG: Interpolation: max elements per row 0<br>
> > > > HYPRE BoomerAMG: Number of levels of aggressive coarsening 0<br>
> > > > HYPRE BoomerAMG: Number of paths for aggressive coarsening 1<br>
> > > > HYPRE BoomerAMG: Maximum row sums 0.9<br>
> > > > HYPRE BoomerAMG: Sweeps down 1<br>
> > > > HYPRE BoomerAMG: Sweeps up 1<br>
> > > > HYPRE BoomerAMG: Sweeps on coarse 1<br>
> > > > HYPRE BoomerAMG: Relax down symmetric-SOR/Jacobi<br>
> > > > HYPRE BoomerAMG: Relax up symmetric-SOR/Jacobi<br>
> > > > HYPRE BoomerAMG: Relax on coarse Gaussian-elimination<br>
> > > > HYPRE BoomerAMG: Relax weight (all) 1<br>
> > > > HYPRE BoomerAMG: Outer relax weight (all) 1<br>
> > > > HYPRE BoomerAMG: Using CF-relaxation<br>
> > > > HYPRE BoomerAMG: Measure type local<br>
> > > > HYPRE BoomerAMG: Coarsen type PMIS<br>
> > > > HYPRE BoomerAMG: Interpolation type classical<br>
> > > > linear system matrix = precond matrix:<br>
> > > > Mat Object: (fieldsplit_u_) 4 MPI processes<br>
> > > > type: mpiaij<br>
> > > > rows=938910, cols=938910, bs=3<br>
> > > > total: nonzeros=8.60906e+07, allocated nonzeros=8.60906e+07<br>
> > > > total number of mallocs used during MatSetValues calls =0<br>
> > > > using I-node (on process 0) routines: found 78749 nodes, limit used is 5<br>
> > > > Split number 1 Defined by IS<br>
> > > > KSP Object: (fieldsplit_wp_) 4 MPI processes<br>
> > > > type: preonly<br>
> > > > maximum iterations=10000, initial guess is zero<br>
> > > > tolerances: relative=1e-05, absolute=1e-50, divergence=10000<br>
> > > > left preconditioning<br>
> > > > using NONE norm type for convergence test<br>
> > > > PC Object: (fieldsplit_wp_) 4 MPI processes<br>
> > > > type: lu<br>
> > > > LU: out-of-place factorization<br>
> > > > tolerance for zero pivot 2.22045e-14<br>
> > > > matrix ordering: natural<br>
> > > > factor fill ratio given 0, needed 0<br>
> > > > Factored matrix follows:<br>
> > > > Mat Object: 4 MPI processes<br>
> > > > type: mpiaij<br>
> > > > rows=34141, cols=34141<br>
> > > > package used to perform factorization: pastix<br>
> > > > Error : -nan<br>
> > > > Error : -nan<br>
> > > > total: nonzeros=0, allocated nonzeros=0<br>
> > > > Error : -nan<br>
> > > > total number of mallocs used during MatSetValues calls =0<br>
> > > > PaStiX run parameters:<br>
> > > > Matrix type : Symmetric<br>
> > > > Level of printing (0,1,2): 0<br>
> > > > Number of refinements iterations : 0<br>
> > > > Error : -nan<br>
> > > > linear system matrix = precond matrix:<br>
> > > > Mat Object: (fieldsplit_wp_) 4 MPI processes<br>
> > > > type: mpiaij<br>
> > > > rows=34141, cols=34141<br>
> > > > total: nonzeros=485655, allocated nonzeros=485655<br>
> > > > total number of mallocs used during MatSetValues calls =0<br>
> > > > not using I-node (on process 0) routines<br>
> > > > linear system matrix = precond matrix:<br>
> > > > Mat Object: 4 MPI processes<br>
> > > > type: mpiaij<br>
> > > > rows=973051, cols=973051<br>
> > > > total: nonzeros=9.90037e+07, allocated nonzeros=9.90037e+07<br>
> > > > total number of mallocs used during MatSetValues calls =0<br>
> > > > using I-node (on process 0) routines: found 78749 nodes, limit used is 5<br>
> > > ><br>
> > > > The pattern of convergence gives a hint that this system is somehow bad/singular. But I don't know why the preconditioned error goes up too high. Anyone has an idea?<br>
> > > ><br>
> > > > Best regards<br>
> > > > Giang Bui<br>
> > > ><br>
> > ><br>
> > ><br>
> ><br>
> ><br>
><br>
><br>
<br>
</div></div></blockquote></div><br></div></div></div>