Global Stop Condition (Number of Iterations)

Generally, the number of optimization cycles should be limited per default to a certain number to limit the computation time for optimizations with convergence problems.

The stop criterion is the maximum number of optimization iterations, which is default 50 for both sensitivity-based and controller-based optimizations. When the maximum number of optimization iterations is reached, the optimization algorithm always stops independent of other criteria. The allowed maximum number of optimization iterations can be increased or decreased by the user. This is defined by the parameter ITER_MAX of the STOP command. 


STOP
 ID_NAME  = global_stop
 ITER_MAX = 5
END_

where ITER_MAX is decreased to 5.

A global stop condition is essential to limit the number of design cycles in case no convergence is obtained. User-defined stop conditions adapted to the task (instead of using the default values) might improve efficiency.

Since a "partially optimized model" can be used as a starting model for a subsequent optimization, it makes sense to calculate first a few design cycles and then to use information from the optimization result to calculate more design cycles with adjusted settings.

Important:
  • For simple shape optimization tasks, it is often sufficient to limit the number of iterations to 5 or 10. For more complex setups, the iterations should be increased to around 25, which is enough for many cases. However, there are setups where even more iterations are needed and it is hard to guess a number that is valid for all cases.
  • The global stop criterion leads to a stop of the optimization, independent of a complete convergence of the result. For shape optimization tasks this is no drawback as the optimization task can be continued for some more steps using the input file of the last iteration as start file.