On Tue, Oct 27, 2015 at 9:10 AM, Matthew Knepley <[email protected]> wrote:
> On Tue, Oct 27, 2015 at 9:06 AM, Gary Rebt <[email protected]> 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 >> > > 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 >> 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
