Fitness Convergence Terminator

The fitness convergence terminator stops the optimization, when there has been hardly any change in the best population fitness (within percentual or absolute distance) for a certain time, given in generations or fitness calls.
Be aware that, if the optimization is allowed to be non-monotonic, such as for (,)-ES strategies, and if the optimum is close to zero, it may happen that the fitness fluctuates due to numeric issues and does not easily converge in a relative measure.