What solver convergence looks like
Channel: OpenMDAO
Date: 2022-09-15

A system is converged when the residuals are close to 0 within a tolerance. How this is achieved depends on what solver you use, but generally you want your residuals to decrease as computationally quickly as possible.

0:00 - Intro
1:00 - The basic idea of convergence
2:36 - How to tell when a system is converged
6:54 - Convergence in the terminal
13:25 - Conclusion

Accompanying Python notebook: https://openmdao.github.io/PracticalMDO/Notebooks/ModelConstruction/what_solver_convergence_looks_like.html

Relevant OpenMDAO doc pages:
http://openmdao.org/twodocs/versions/latest/basic_user_guide/multidisciplinary_optimization/sellar.html
https://openmdao.org/twodocs/versions/latest/features/debugging/debugging_solvers.html
http://openmdao.org/twodocs/versions/latest/features/core_features/controlling_solver_behavior/set_solvers.html
http://openmdao.org/twodocs/versions/latest/features/core_features/controlling_solver_behavior/solver_options.html

Check out Sections 3.3-3.8 (especially Sec. 3.7 "Rate of Convergence") in the Engineering Design Optimization textbook by Martins and Ning for an in-depth theoretical view of solvers, available for free at: https://mdobook.github.io/