I did a quick test: 1) ilu with any shift type does not converge 2) gmres/4 bjacobi/ilu + shift_type nonzero does not converge 3) mpiexec -n 4 ./ex10 -f0 $D/mat.bin -rhs 0 -ksp_monitor -sub_pc_type lu -sub_pc_factor_shift_type nonzero ... 0 KSP Residual norm 3.284826093129e+03 1 KSP Residual norm 2.802972716423e+03 2 KSP Residual norm 2.039112137210e+03 ... 24 KSP Residual norm 2.666350543810e-02 Number of iterations = 24 Residual norm 0.0179698
Hong On Tue, Oct 27, 2015 at 1:50 PM, Barry Smith <bsm...@mcs.anl.gov> wrote: > > > On Oct 27, 2015, at 12:40 PM, Hong <hzh...@mcs.anl.gov> wrote: > > > > Here is the reason why it does not converge: > > ./ex10 -f0 $D/mat.bin -rhs 0 -ksp_monitor_true_residual -ksp_view > -ksp_converged_reason > > Linear solve did not converge due to DIVERGED_NANORINF iterations 0 > > This means it found a zero pivot either in the factorization or in the > first attempt to do a triangular solve. You can try > > -pc_factor_nonzeros_along_diagonal > > and or > > -pc_factor_shift_type nonzero > > to generate a usable LU factorization but these are ad hoc fixes. > > > > Barry > > > > > KSP Object: 1 MPI processes > > type: gmres > > GMRES: restart=30, using Classical (unmodified) Gram-Schmidt > Orthogonalization with no iterative refinement > > GMRES: happy breakdown tolerance 1e-30 > > maximum iterations=10000, initial guess is zero > > tolerances: relative=1e-05, absolute=1e-50, divergence=10000. > > left preconditioning > > using PRECONDITIONED norm type for convergence test > > PC Object: 1 MPI processes > > type: ilu > > ILU: out-of-place factorization > > ... > > > > Hong > > > > On Tue, Oct 27, 2015 at 12:36 PM, Hong <hzh...@mcs.anl.gov> wrote: > > Matt: > > On Tue, Oct 27, 2015 at 11:13 AM, Hong <hzh...@mcs.anl.gov> wrote: > > Gary : > > I tested your mat.bin using > > petsc/src/ksp/ksp/examples/tutorials/ex10.c > > ./ex10 -f0 $D/mat.bin -rhs 0 -ksp_monitor_true_residual -ksp_view > > ... > > Mat Object: 1 MPI processes > > type: seqaij > > rows=588, cols=588 > > total: nonzeros=11274, allocated nonzeros=11274 > > total number of mallocs used during MatSetValues calls =0 > > using I-node routines: found 291 nodes, limit used is 5 > > Number of iterations = 0 > > Residual norm 24.2487 > > > > It does not converge, neither hangs. > > > > This is the default GMRES/ILU. > > Hong > > > > As you said, matrix is non-singular, LU gives a solution > > ./ex10 -f0 $D/mat.bin -rhs 0 -ksp_monitor_true_residual -pc_type lu > > 0 KSP preconditioned resid norm 3.298891225772e+03 true resid norm > 2.424871130596e+01 ||r(i)||/||b|| 1.000000000000e+00 > > 1 KSP preconditioned resid norm 1.918157196467e-12 true resid norm > 5.039404549028e-13 ||r(i)||/||b|| 2.078215409241e-14 > > Number of iterations = 1 > > Residual norm < 1.e-12 > > > > Is this the same matrix as you mentioned? > > > > Hong, could you run ILU on it as well? > > > > Thanks, > > > > Matt > > > > Hong > > > > > > > > > > On Tue, Oct 27, 2015 at 9:10 AM, Matthew Knepley <knep...@gmail.com> > wrote: > > > > On Tue, Oct 27, 2015 at 9:06 AM, Gary Rebt <gary.r...@gmx.ch[ > gary.r...@gmx.ch]> wrote: > > > > Dear petsc-users, > > > > While using the FEniCS package to Solve a simple Stokes' flow problem, I > have run into problems with PETSc preconditioners. In particular, I would > like to use ILU (no parallel version) along with GMRES to solve my linear > system but the solver just hangs indefinitely at > MatLUFactorNumeric_SeqAIJ_Inode without outputting anything. CPU usage is > at 100% but even for a tiny system (59x59 for minimal test case), the > solver does not seem to manage to push through it after 30 mins. > > > > PETSc version is 3.6 and the matrix for the minimal test case is as > follows : > > http://pastebin.com/t3fvdkaS[http://pastebin.com/t3fvdkaS] > > > > Hanging is a bug. We will check it out. > > > > I do not have any way to read in this ASCII. Can you output a binary > version > > > > -mat_view binary:mat.bin > > > > Thanks, > > > > Matt > > > > > > It contains zero diagonal entries, has a condition number of around 1e3 > but is definitely non-singular. Direct solvers manage to solve the system > as well as GMRES without preconditioner (although after many iterations for > a 59x59 system..). > > > > This will never work. Direct solvers work because they pivot away the > zeros, but ILU is defined by having no pivoting. > > > > Thanks, > > > > Matt > > > > > > Playing with the available options here > http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCILU.html[http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCILU.html] > did not seem to solve the issue (even after activating diagonal_fill and/or > nonzeros_along_diagonal) although sometimes error 71 is returned which > stands for zero pivot detected. Are there yet other options that I have not > considered? The default ILU factorization in MATLAB returns satisfactory > problems without errors so surely it must be possible with PETSc? > > > > As for the choice of ILU, I agree it might be suboptimal in this setting > but I do need it for benchmarking purposes. > > > > Best regards, > > > > Gary > > -- > > 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 > > > > > >
