About Optimization Feasibility

Optimization techniques classify the designs that they evaluate into feasible and infeasible designs. A design is feasible if it satisfies all the constraints placed upon the design space during execution of an optimization technique. A design is infeasible if it violates one or more of those constraints.

The concept of feasibility is used to distinguish:

  • Designs that are physically constructible from designs that are not

  • Designs that fit as parts within a larger assembly from designs that do not fit

  • Designs that satisfy minimal performance requirements from designs that do not

For optimization, the term “constraints” specifically means “output constraints,” which are defined as requirements placed upon the output parameters of a design space because output values cannot be controlled directly. Typically, technique implementations (and Optimization Process Composer implementations in particular) enforce input constraints—they evaluate only designs within the specified design space—so the notion of “violation” does not apply to them.

Assigned feasibility codes are meaningful only for designs that have been evaluated successfully. The following table describes the design feasibility codes:

Value Designation Meaning
0 Simulation code failed (no results) This design is unusable.
1 Infeasible (constraint violations) This design violates one or more constraints. This design is not as good as the previous best design (which is necessarily also infeasible), but it is not necessarily the worst design.
2 Infeasible - tie This design violates one or more constraints. This design is as good as the previous best design.
3 Infeasible - better This design violates one or more constraints. This design is better than the previous best design.
7 Feasible This design satisfies all constraints. This design is not as good as the previous best design. There may be an infeasible design that could be considered better than this design if the constraint violation is small.
8 Feasible - tie This design satisfies all constraints. This design is as good as the previous best feasible design and is better than any infeasible design.
9 Feasible - better This design satisfies all constraints. This design is better than the previous best (feasible or infeasible) design.