optuna.visualization.matplotlib.plot_contour(study, params=None, *, target=None, target_name='Objective Value')[source]

Plot the parameter relationship as contour plot in a study with Matplotlib.

Note that, if a parameter contains missing values, a trial with missing values is not plotted.

See also

Please refer to optuna.visualization.plot_contour() for an example.


Output figures of this Matplotlib-based plot_contour() function would be different from those of the Plotly-based plot_contour().


The following code snippet shows how to plot the parameter relationship as contour plot.

import optuna

def objective(trial):
    x = trial.suggest_float("x", -100, 100)
    y = trial.suggest_categorical("y", [-1, 0, 1])
    return x ** 2 + y

sampler = optuna.samplers.TPESampler(seed=10)
study = optuna.create_study(sampler=sampler)
study.optimize(objective, n_trials=30)

optuna.visualization.matplotlib.plot_contour(study, params=["x", "y"])
  • study (optuna.study.study.Study) – A Study object whose trials are plotted for their target values.

  • params (Optional[List[str]]) – Parameter list to visualize. The default is all parameters.

  • target (Optional[Callable[[optuna.trial._frozen.FrozenTrial], float]]) –

    A function to specify the value to display. If it is None and study is being used for single-objective optimization, the objective values are plotted.


    Specify this argument if study is being used for multi-objective optimization.

  • target_name (str) – Target’s name to display on the color bar.


A matplotlib.axes.Axes object.


ValueError – If target is None and study is being used for multi-objective optimization.

Return type



Added in v2.2.0 as an experimental feature. The interface may change in newer versions without prior notice. See https://github.com/optuna/optuna/releases/tag/v2.2.0.