> On 12 Jul 2022, at 2:32 PM, Matthew Knepley <[email protected]> wrote: > > On Mon, Jul 11, 2022 at 1:17 PM Pierre Jolivet <[email protected] > <mailto:[email protected]>> wrote: > Hello, > Could anyone help me understand what is going on in the following example, > please? > I have a VecNest. > I either: a) initialize all values to 0.0, then set a specific part of the > vector to nonzero or b) initialize a part of the vector to 0.0 and set the > other part to nonzero. > I don’t see why a) and b) produce different results. > > $ ./ex1111 -pc_type fieldsplit -ksp_monitor_true_residual > -ksp_converged_reason -fieldsplit_pc_type jacobi -ksp_pc_side right > -ksp_view_final_residual -nest_subvec true > 0 KSP unpreconditioned resid norm 8.375635517980e-01 true resid norm > 8.375635517980e-01 ||r(i)||/||b|| 1.000000000000e+00 > 1 KSP unpreconditioned resid norm 4.748816884247e-01 true resid norm > 4.748816884247e-01 ||r(i)||/||b|| 5.669798875623e-01 > 2 KSP unpreconditioned resid norm 4.713006778679e-01 true resid norm > 4.713006778679e-01 ||r(i)||/||b|| 5.627043784990e-01 > 3 KSP unpreconditioned resid norm 7.092979927129e-02 true resid norm > 7.092979927129e-02 ||r(i)||/||b|| 8.468587144106e-02 > 4 KSP unpreconditioned resid norm 1.457836310255e-02 true resid norm > 1.457836310255e-02 ||r(i)||/||b|| 1.740567992870e-02 > 5 KSP unpreconditioned resid norm 1.625040500524e-14 true resid norm > 1.633468028779e-14 ||r(i)||/||b|| 1.950261595401e-14 > Linear solve converged due to CONVERGED_RTOL iterations 5 > KSP final norm of residual 1.63347e-14 > $ ./ex1111 -pc_type fieldsplit -ksp_monitor_true_residual > -ksp_converged_reason -fieldsplit_pc_type jacobi -ksp_pc_side right > -ksp_view_final_residual -nest_subvec false > 0 KSP unpreconditioned resid norm 0.000000000000e+00 true resid norm > 8.375635517980e-01 ||r(i)||/||b|| inf > Linear solve converged due to CONVERGED_ATOL iterations 0 > KSP final norm of residual 0.837564 > > I find if I assemble the vector, I get the same answers. Will try to figure > out what assembly is doing.
It’s probably reseting all these values https://petsc.org/main/src/vec/vec/interface/rvector.c.html#line511 <https://petsc.org/main/src/vec/vec/interface/rvector.c.html#line511>, which I believe are being used in VecNorm() inside VecNormalize(). I guess any call to VecNestSubVec() should invalidate those as well, otherwise we get wrong cached norms. I will give this a go. Thanks, Pierre > Thanks, > > Matt > > Thanks, > Pierre > > > > -- > 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.cse.buffalo.edu/~knepley/>
