multi-objective sampler 类

optuna.multi_objective.samplers.BaseMultiObjectiveSampler	multi-objective sampler 基类。
optuna.multi_objective.samplers.NSGAIIMultiObjectiveSampler	使用 NSGA-II 算法的 Multi-objective sampler。
optuna.multi_objective.samplers.RandomMultiObjectiveSampler	Multi-objective sampler using random sampling.
optuna.multi_objective.samplers.MOTPEMultiObjectiveSampler	采用 MOTPE 算法的多目标sampler。