how to set the 'target' in multi-objective optimization

Environment

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Description

when I run the code ‘optuna.visualization.matplotlib.plot_parallel_coordinate(study)’ , meet the error: If the study is being used for multi-objective optimization, please specify the target.

So, I want to consult you how to set the target, Can give me a example? Thank you very much!

Error messages, stack traces, or logs

If the `study` is being used for multi-objective optimization, please specify the `target`.

Steps to reproduce

1.import optuna 2.algo = optuna.samplers.TPESampler(n_startup_trials = 10, n_ei_candidates = 24)

3.study = optuna.create_study(sampler = algo, directions=[“minimize”, “maximize”]) 4.study.optimize(objective, n_trials=300, timeout=300)

[himkt]

@pistachio-xin Sorry for confusing you, the problem I mentioned happens only on the master branch of Optuna and it doesn’t happen on our published versions of Optuna. You don’t need to take care of it. 👍

[pistachio-xin]

Hi@himkt @nzw0301, Thanks for your help, I run right for this issue and got the right figure. For the issue from @himkt, In my test code, I can saw the function of optimization direction in the multi-objective optimization problems, but maybe I didn’t understand your means.