Since your Jacobian matrix is small, it is possible to compare your hand-written Jacobian with the finite-difference approximation directly. Add -snes_test_jacobian_view to print out the matrices. Then you can see exactly where the difference is.
Hong > On Oct 27, 2021, at 12:47 AM, 仓宇 <yhcy1...@gmail.com> wrote: > > Thanks for your kind reply. > > Several comparison tests have been performed. Attached are execution > output files. Below are corresponding descriptions. > > good.txt -- Run without hand-coded jacobian, solution converged, with > option '-ts_monitor -snes_monitor -snes_converged_reason > -ksp_monitor_true_residual -ksp_converged_reason'; > jac1.txt -- Run with hand-coded jacobian, does not converge, with > option '-ts_monitor -snes_monitor -snes_converged_reason > -ksp_monitor_true_residual -ksp_converged_reason -snes_test_jacobian'; > jac2.txt -- Run with hand-coded jacobian, does not converge, with > option '-ts_monitor -snes_monitor -snes_converged_reason > -ksp_monitor_true_residual -ksp_converged_reason -snes_test_jacobian > -ksp_view'; > jac3.txt -- Run with hand-coded jacobian, does not converge, with > option '-ts_monitor -snes_monitor -snes_converged_reason > -ksp_monitor_true_residual -ksp_converged_reason -snes_test_jacobian > -ksp_view -ts_max_snes_failures -1 '; > > The problem under consideration contains an eigen-value to be solved, > making the first diagonal element of the jacobian matrix being zero. > From these outputs, it seems that the PC failed to factorize, which is > caused by this 0 diagonal element. But I'm wondering why it works > with jacobian matrix generated by finite-difference? Would employing > DMDA for discretization be helpful? > > Regards > > Yu Cang > > Barry Smith <bsm...@petsc.dev> 于2021年10月25日周一 下午10:50写道： >> >> >> 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 >> > <jac3.txt><jac2.txt><jac1.txt><good.txt>
