On Thu, Sep 27, 2012 at 2:01 PM, Zou (Non-US), Ling <ling.zou at inl.gov>wrote:
> Dear all, > > I have a question on the PETSc option '-snes_mf_operator'. > I am reading the <PETSc Users Manual Revision 3.3>. On page 100, 2nd > paragraph, it says: > > > ============================================================================== > "However, it allows us to check the analytic Jacobian we construct in > FormJacobian() by passing the -snes_mf_operator flag. This causes PETSc to > approximate the Jacobian using finite differencing of the function > evaluation (discussed in section 5.6), and the analytic Jacobian becomes > merely the preconditioner." > > ============================================================================== > > I wonder, if the '-snes_mf_operator' option is used, the Jacobian will > always be calculated from the finite difference method while > ignore whatever has been provided from user. > Yes, yhe action will be FD, but it will take the user provided operator to form a preconditioner from. Matt > One more question, if I pass '-snes' to PETSc, since it is direct Newton's > method, I assume it will explicitly construct a Jacobian. Does this > Jacobian come from user provided Jacobian or from the finite difference > Jacobian? > > > Thanks, > > > Ling > > -- 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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120927/37e89116/attachment.html>