In practice, good programs are rarely judged by only one criterion. Then, GP can become a multiobjective problem:
For example:
Thus, multiobjective GP does not seek one best solution; instead, it seeks a pareto set.
We say that a solution dominates if is no worse in every objective, and is strictly better in at least one objective.
- is dominated by because they have the same error but is smaller. and reflect a real trade-off.
Practically, the final choice depends on what we care about.