[petsc-users] Problem with SNES convergence

[Ling Zou]

1) My experience is that this kind of bug or sudden death (everything is fine till suddenly something is broken) is very difficult to debug/fix. I looked at your txt files and could not give any quick comments. Maybe PETSc developers have better idea on this.

2) I do have successful experience on reducing time step size when PETSc fails solving or my own piece of code throws an exception. If you are interested, I can share them.


-Ling

________________________________
From: petsc-users <petsc-users-bounces at mcs.anl.gov> on behalf of Rahul Samala <srahul_05 at yahoo.co.in>
Sent: Wednesday, August 29, 2018 8:36:58 AM
To: PETSc Users List
Subject: [petsc-users] Problem with SNES convergence

Hello PetSc users,

1)  I have problem with SNES convergence. I call SNESSolve  in a time loop and use the inbuilt Jacobian feature. The code works fine for about 5380 time steps after which it breaks down. The solution till that point looks fine. I have used newtonls of type l2. (newtontr and others aren't working). Since I have used inbuilt Jacobian feature and the code worked for about 5000 time steps I don't understand the reason for failure, is it an incorrect function evaluation?  Attached are the outputs with -pc_type lu and ilu along with -snes_linesearch_type l2 -snes_converged_reason -snes_monitor -snes_view -ksp_converged_reason -ksp_monitor_true_residual

2)  How to get hold of failure signal, like Nonlinear solve DIVERGED_MAX_IT or DIVERGED_LINEAR_SOLVE so that whenever it occurs I can use a reduced time step and see if the code converges.

Thank you,
Rahul.

output_ilu.txt<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Ffile%2Fd%2F12bAiJm0i2NEmv7NXld6LSuzUVpNrLwSA%2Fview%3Fusp%3Dsharing&data=02%7C01%7Cling.zou%40inl.gov%7C08b7659327d741a8d7f408d60dbceedf%7C4cf464b7869a42368da2a98566485554%7C0%7C0%7C636711502445785646&sdata=QdD33Cfq8FN3mTLEKUp3Z3gspmzKkpIMRssXj5zbaz4%3D&reserved=0>

<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Ffile%2Fd%2F12bAiJm0i2NEmv7NXld6LSuzUVpNrLwSA%2Fview%3Fusp%3Dsharing&data=02%7C01%7Cling.zou%40inl.gov%7C08b7659327d741a8d7f408d60dbceedf%7C4cf464b7869a42368da2a98566485554%7C0%7C0%7C636711502445795654&sdata=u3Dl8rahfOQ8I4PEDYyk2nPL3WzQsNNhoca9f0sZXJk%3D&reserved=0>




[https://s.yimg.com/nq/storm/assets/enhancrV2/23/logos/google.png]
output_ilu.txt






output_lu.txt<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Ffile%2Fd%2F1CbQuLLIVtkACo6eedMmMQvX41TvjtoiQ%2Fview%3Fusp%3Dsharing&data=02%7C01%7Cling.zou%40inl.gov%7C08b7659327d741a8d7f408d60dbceedf%7C4cf464b7869a42368da2a98566485554%7C0%7C0%7C636711502445795654&sdata=x%2Fh2q4lObUJHSpmYeSfQFUtUyKRkYIVhV92ugWO7WX8%3D&reserved=0>

<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Ffile%2Fd%2F1CbQuLLIVtkACo6eedMmMQvX41TvjtoiQ%2Fview%3Fusp%3Dsharing&data=02%7C01%7Cling.zou%40inl.gov%7C08b7659327d741a8d7f408d60dbceedf%7C4cf464b7869a42368da2a98566485554%7C0%7C0%7C636711502445805667&sdata=KGqCZLF%2FbCnVYSim2o49V5bhwHdMQzZkxpQvVqwxRy0%3D&reserved=0>




[https://s.yimg.com/nq/storm/assets/enhancrV2/23/logos/google.png]
output_lu.txt





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