What is the reason for nonconvergence of newton solver?

1

You can find problem in google colab in the link below. You can run code to see nonconvergence problem.

https://colab.research.google.com/drive/1oBj0oFPgXDPBuYIBB7fEIGvgcnOpa_6x?usp=sharing

Thanks in advance for your help.

2

Please read the guidelines for questions: Read before posting: How do I get my question answered?
And supply a minimal code example.

3

Minimal code example is in the colab link. I used dolfin version: 2019.1.0. This is the error that I obtained.
*** ------------------------------------------------------------------------- *** DOLFIN encountered an error. If you are not able to resolve this issue *** using the information listed below, you can ask for help at *** *** fenics-support@googlegroups.com *** *** Remember to include the error message listed below and, if possible, *** include a minimal running example to reproduce the error. *** *** ------------------------------------------------------------------------- *** Error: Unable to solve nonlinear system with NewtonSolver. *** Reason: Newton solver did not converge because maximum number of iterations reached. *** Where: This error was encountered inside NewtonSolver.cpp. *** Process: 0 *** *** DOLFIN version: 2019.1.0 *** Git changeset: unknown *** -------------------------------------------------------------------------

Minimal code example is in this link

4

I would not call it a minimal example, as it consists of three coupled PDEs and a ton of parameters. I would suggest trying to simplify the problem, and see if your problem persist. By simplifying the example, it increases the likelihood that anyone will have time to look at your problem.

At least, you should post the mathematical formulation of your problem, and not just a link to an external code, as this contributes very little to guiding others in the future (as your code might change, or the link is deleted).

In the case of your problem, it seems like the issue is that you are using the incremental convergence, which causes the algorithm to diverge after a couple of iterations. By removing the incremental convergence criterion, the solver converges.