ratio is || A - Afd || /||A|| where |||| is the frobenus norm and difference is || A - Afd ||.
Try using -snes_mf -pc_type lu This can often converge even if the A you provide is wrong, so if this convergence sine then likely the Jacobian is wrong. It is also possible that the function evaluation has a bug. http://www.mcs.anl.gov/petsc/documentation/faq.html#newton Barry On Dec 19, 2013, at 4:26 PM, Que Cat <quecat...@gmail.com> wrote: > Hello, > > I use SNES to solve the non linear coupled equations. I have checked the > hand-coded jacobian with -snes_type test and received the result: > Norm of matrix ratio 1.39606e-23 difference 1.53372e-14 (user-defined state) > Norm of matrix ratio 3.03157e-10 difference 0.33305 (constant state -1.0) > Norm of matrix ratio 3.03157e-10 difference 0.33305 (constant state 1.0) > It said that " if the ratio is O(1.e-8), the hand-coded Jacobian is probably > correct." What is the second paramenter "difference 1.53372e-14 ...."? Does > it play any role in checking the accuracy of hand-coded jacobian? > > The SNES solver for failed with the reason -6 "the line search failed". I > tried with all other line search method stated in the PETSC manual, but they > all failed. > > I tried to figure out what is wrong with my code? Could you please give me > any recommendation to direct me how to check my code? I appreciate your help. > > QUe >
