Is this coming from a Stokes-like problem? Barry
On Aug 3, 2010, at 10:54 PM, Filippo Spiga wrote: > Dear Hong, >> This confirms that your Jacobian is singular, thus none of linear >> solvers would work. > > So do any preconditioner not help me to solve the problem? > > I put some stuff here: http://tinyurl.com/fil-petsc > - "A_LS.m" is matrix (saved by PETSc) > - "b_LS-m" > - the file "eigenvalues_A" contains the eigenvalues of the matrix A, computed > by MATLAB. > > I used "-pc_type lu" and 1 only processor. The result is the same of my > previous email (*). > > Anyway if I solve the problem using MATLAB I get the right solution. The > formulation seems correct. To be honest, the eigenvalues don't say me > nothing. But I'm a computer scientist, not a mathematician. I'm not able to > recognize which preconditioner I should use or which modifications (scaling > all/part of the rows? reformulate the system in another way?...) do to solve > the problem. From my side, it is not possible to try all the preconditioners > and also it is not the right way... > > Once again, thanks. > > (*) > [0|23:14:58]: unknown: MatLUFactorNumeric_SeqAIJ() line 668 in > src/mat/impls/aij/seq/aijfact.c: Zero pivot row 1 value 0 tolerance > 2.77778e-14 * rowsum 0.0277778 > > -- > > Filippo SPIGA > > ?Nobody will drive us out of Cantor's paradise.? > -- David Hilbert >
