Fande, '-pc_factor_shift_amount 1' is huge. Try use petsc default shift amount '1.e-14' by '-pc_factor_shift_type nonzero' only.
Hong On Tue, Oct 10, 2017 at 9:40 AM, Matthew Knepley <[email protected]> wrote: > On Tue, Oct 10, 2017 at 10:36 AM, Kong, Fande <[email protected]> wrote: > >> Hi Developers, >> >> I am trying to use the native LU in PETSc to compute a matrix (arising >> from a fluid-structure interaction problem). I encounter a zero pivot. The >> matrix gives the wrong Newton direction when using "-pc_factor_shift_type >> nonzero -pc_factor_shift_amount 1". I hence guess the matrix is >> singular. >> >> Any easy way to detect if or not the matrix is singular?? >> > > That is the easiest way, namely having LU fail. You can catch the failure > and do something useful. > > Matt > > >> Fande, >> > > > > -- > 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 > > https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/> >
