On May 5, 2010, at 10:08 AM, Matthew Knepley wrote: > Try using -snes_mf which will approximate the Jacobian automatically.
You can also use -snes_type test -snes_test_display (for a small problem). Also try runs with -snes_monitor -ksp_monitor -ksp_converged_reason -snes_converged_reason and try also -info for lots of information about the line search. You can also try running with -pc_type lu to eliminate any chance that failure of the linear solver is the problem. Barry > > Matt > > 2010/5/5 ????Leping Chen? <chenleping at yahoo.cn> > petsc teams, > > When I use SNES, I find my program iterated many times but x vector and > residual vector > > remained unchanged, that is to say,no convergence.I used finite difference > jacobian approximations, > > but I cannot confirm the jacobian matrix structure is right.Whether the > matrix structure will influence > > the convergence of SNES or not? Why does my x vector and residual vector > remained unchanged? > > call FormJacobian(snes,x,J,J,flag,dummy,ierr) > call MatGetColoring(J,MATCOLORING_SL,iscoloring,ierr) > call MatFDColoringCreate(J,iscoloring,fdcoloring,ierr) > call ISColoringDestroy(iscoloring,ierr) > call MatFDColoringSetFromOptions(fdcoloring,ierr) > call MatFDColoringSetFunction(fdcoloring,FormFunction, > & PETSC_NULL_OBJECT,ierr) > call SNESSetJacobian(snes,J,J,SNESDefaultComputeJacobianColor, > & fdcoloring,ierr) > call SNESGetKSP(snes,ksp,ierr) > call KSPGetPC(ksp,pc,ierr) > call SNESSolve(snes,PETSC_NULL_OBJECT,petscu,ierr) > Thanks, > leping > > > > > -- > 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/20100505/4ce9ebae/attachment.htm>
