> > > what is clear is that your "A" is indefinite, so GMRES or common > > iterative solvers can not works. > > That's not true, of course: GMRES works just fine for indefinite systems, > as do many other iterative solvers. However, CG does not work with > indefinite systems.
W, thanks for your correction :) I just want to add this fact that: your preconditioners may not handle diagonal singularities, e.g. with diagonal preconditioner zero diag. may cause problem (scaling by 1/zero), further, ILU without pivoting also fails for the case of zero diagonals. Cheers RT
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