On 07/22/2012 05:14 PM, Jed Brown wrote: > On Sun, Jul 22, 2012 at 9:49 AM, Umut Tabak <u.tabak at tudelft.nl > <mailto:u.tabak at tudelft.nl>> wrote: > > Dear all, > > I am testing some iterative methods with MATLAB and aside with > PETSc however I have a question which might be answered in the > documentation however I could not find that? > > In MATLAB, at least on recent versions, one can specify a drop > tolerance for the incomplete cholesky preconditioner, I was > wondering if the same is possible with PETSc or not? > > > You can get an ILUT using MatSuperluSetILUDropTol > (-mat_superlu_ilu_droptol) or from Hypre's PILUT (-pc_hypre_pilut_tol).. Dear Jed Thanks for this tip, I will try... > > > One more question, is the condition number order 1e+6(estimated > with condest in MATLAB) rather high for an iterative method? With > icc, with a drop tolerance of 1e-3 or 1e-4, as a preconditioner to > pcg, I can get decent iteration numbers to convergence in MATLAB, > it is sometimes even faster than solving the system with the > available factorization information and I was wondering if I can > make it faster with some other options in PETSc or not? > > > What continuum equations are you solving? What discretization? Helmholtz equation, 3d discretization of a fluid domain, basically the operator is singular however for my problem I can delete one of the rows of the matrix, for this case, I and get a non-singular operator that I can continue my operations, basically, I am getting a matrix with size n-1, where original problem size is n. However, this application is pretty problem specific, then I can use this full-rank matrix in linear solutions. The condition number estimate belongs to this full-rank matrix that is extracted from the original singular operator...
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