It is definitely unexpected that -snes_test_jacobian verifies the Jacobian as matching but the solve process is completely different.
Please run with -snes_monitor -snes_converged_reason -ksp_monitor_true_residual -ksp_converged_reason -snes_test_jacobian and send all the output Barry > On Oct 25, 2021, at 9:53 AM, 仓宇 <yhcy1...@gmail.com> wrote: > > I'm using TS to solve a set of DAE, which originates from a > one-dimensional problem. The grid points are uniformly distributed. > For simplicity, the DMDA is not employed for discretization. > > At first, only the residual function is prescribed through > 'TSSetIFunction', and PETSC produces converged results. However, after > providing hand-coded Jacobian through 'TSSetIJacobian', the internal > SNES object fails (residual norm does not change), and TS reports > 'DIVERGED_STEP_REJECTED'. > > I have tried to add the option '-snes_test_jacobian' to see if the > hand-coded jacobian is somewhere wrong, but it shows '||J - > Jfd||_F/||J||_F = 1.07488e-10, ||J - Jfd||_F = 2.14458e-07', > indicating that the hand-coded jacobian is correct. > > Then, I added a monitor for the internal SNES object through > 'SNESMonitorSet', in which the solution vector will be displayed at > each iteration. It is interesting to find that, if the jacobian is not > provided, meaning finite-difference is utilized for jacobian > evaluation internally, the solution vector converges to steady > solution and the SNES residual norm is reduced continuously. However, > it turns out that, as long as the jacobian is provided, the solution > vector will NEVER get changed! So the solution procedure stucked! > > This is quite strange! Hope to get some advice. > PETSC version=3.14.6, program run in serial mode. > > Regards > > Yu Cang
