<html><head></head><body><div style="font-family: Verdana;font-size: 12.0px;"><div>Dear petsc-users,</div>
<div> </div>
<div>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.</div>
<div> </div>
<div>PETSc version is 3.6 and the matrix for the minimal test case is as follows :</div>
<div>http://pastebin.com/t3fvdkaS</div>
<div> </div>
<div>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..).</div>
<div> </div>
<div>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?</div>
<div> </div>
<div>As for the choice of ILU, I agree it might be suboptimal in this setting but I do need it for benchmarking purposes.</div>
<div> </div>
<div>Best regards,</div>
<div> </div>
<div>Gary</div></div></body></html>