[petsc-users] question on PETSc option '-snes_mf_operator'

[Zou (Non-US), Ling]

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.

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120927/b23d9336/attachment.html>