Users:Structural Optimization/Optimization Algorithms/Convergence Measures

Motivation

The convergence criteria of optimization problems are collected in a separate module. During the optimization process the optimization algorithm checks with aid of the convergence checker if the fulfills convergence criteria or not. The convergence criteria are separated in strict convergence criteria, weak convergence criteria, and exclusion criteria. If a strict convergence criteria is fulfilled the optimization process stops in any case. If only a weak convergence criteria is fulfilled the method additionally checks if no exclusion criteria is fulfilled. The optimization stops only if no exclusion criteria are fulfilled.

Strict convergence criteria:

• Maximum number of iterations. If the optimization process reaches the maximum number of steps the procedure will be finished.

Soft convergence criteria:

• Actual objective value larger than old objective value
• Actual objective improvement smaller than specified specified minimum value. This minimum value is defined by OBJECTIVE_TOL*initial_objective_improvement. If the actual objective improvement is smaller than this minimum value the convergence criterion is fulfilled.

Exclusion criteria:

• Actual design infeasible
• Number of sequential steps with valid soft convergence criteria smaller than specified limit

Input Parameters

Compulsory Parameters
Parameter	Values, Default(*)	Description
OPT-CONVERGENCE	int	The ID of the convergence module.
CHECK_CONVERGENCE	int	Flag to specify if soft convergence checks should be performed or not (0 - no soft convergence checks, 1 - apply soft convergence checks).
MAX_STEP	int	Maximum number of optimization steps.
OBJECTIVE_TOL	float	Multiplier for initial objective improvement. Required to specify the minimum objective improvement which is necessary for each step.
CONVERGENCE_STEPS	int	Minimum number of sequentially converged steps.

Example of a complete input block:

OPT-CONVERGENCE 1
  CHECK_CONVERGENCE = 1
  MAX_STEP = 20
  OBJECTIVE_TOL = 0.0005
  CONVERGENCE_STEPS = 2

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