On Fri, Mar 18, 2011 at 12:41, Gianluca Meneghello <gianmail at gmail.com>wrote:
> One more thing: what does the three lines stand for then? I was > thinking it was three Newton steps, but I understand it's not... > It is your Jacobian evaluated at user-defined state, constant -1.0, and constant 1.0. I added this to the output for petsc-dev: $ ./ex5 -snes_type test Testing hand-coded Jacobian, if the ratio is O(1.e-8), the hand-coded Jacobian is probably correct. Run with -snes_test_display to show difference of hand-coded and finite difference Jacobian. Norm of matrix ratio 2.77166e-08 difference 2.17871e-07 (user-defined state) Norm of matrix ratio 1.34123e-08 difference 1.23213e-07 (constant state -1.0) Norm of matrix ratio 1.31875e-07 difference 9.05494e-07 (constant state 1.0) [0]PETSC ERROR: SNESSolve() line 2360 in /home/jed/petsc/src/snes/interface/snes.c [0]PETSC ERROR: main() line 220 in src/snes/examples/tutorials/ex5.c > > The output I sent was actually the output of one of your examples. The > one from my own code is > > Testing hand-coded Jacobian, if the ratio is > O(1.e-8), the hand-coded Jacobian is probably correct. > Run with -snes_test_display to show difference > of hand-coded and finite difference Jacobian. > Norm of matrix ratio 9.17257e-08 difference 2.58876e-05 > Is your starting state zero? > Norm of matrix ratio 1.45865e-06 difference 0.000430034 > Norm of matrix ratio 1.47148e-06 difference 0.000429436 > If your problem is ill-conditioned, this might come from differencing error. Try with -mat_fd_type ds to use a slightly more robust scheme. You can also run with -ksp_rtol 1e-12 -pc_type lu -snes_monitor and check if you see quadratic convergence. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110318/42d2eb72/attachment.htm>
