• Design variables are variables that the designer can change. In mathematical terms, they correspond to independent variables. Examples: thickness, dimensions, number of items, etc.
• Objective function is a response that you want to minimize or maximize among the performance indices composed of functions of design variables. In mathematical terms, they correspond to dependent variables. Examples: efficiency, weight, life cycle, etc.
• Constraints are responses that have a range of requirements among the performance indices composed of functions of design variables. In mathematical terms, they correspond to dependent variables. Examples: stiffness, strength, temperature, crash performance, natural frequency, etc.
• The performance indices are basically composed in the form defined above, but they can be freely placed anywhere in the objective function or constraints depending on the situation.
• Here's a hint: the optimization algorithm tends to satisfy the constraints first and then the properties of the objective function.
• Therefore, if the range of constraints is narrow, there are cases where the properties of the objective function (maximization or minimization) do not work as intended.
• If the range of constraints is sufficient, you only need to be located within that range, so you can obtain a solution that focuses on improving the objective function.