Optuna - A hyperparameter optimization framework

Eager search spaces

Automated search for optimal hyperparameters using Python conditionals, loops, and syntax

State-of-the-art algorithms

Efficiently search large spaces and prune unpromising trials for faster results

Easy parallelization

Parallelize hyperparameter searches over multiple threads or processes without modifying code

A simple optimization problem:

1. Define objective function to be optimized. Let's minimize (x - 2)^2
2. Suggest hyperparameter values using trial object. Here, a float value of x is suggested from -10 to 10
3. Create a study object and invoke the optimize method over 100 trials

import optuna

def objective(trial):
    x = trial.suggest_uniform('x', -10, 10)
    return (x - 2) ** 2

study = optuna.create_study()
study.optimize(objective, n_trials=100)

study.best_params  # E.g. {'x': 2.002108042}

colab.research.google

You can optimize PyTorch hyperparameters, such as the number of layers and the number of hidden nodes in each layer, in three steps:

1. Wrap model training with an objective function and return accuracy
2. Suggest hyperparameters using a trial object
3. Create a study object and execute the optimization

import torch

import optuna

# 1. Define an objective function to be maximized.
def objective(trial):

    # 2. Suggest values of the hyperparameters using a trial object.
    n_layers = trial.suggest_int('n_layers', 1, 3)
    layers = []

    in_features = 28 * 28
    for i in range(n_layers):
        out_features = trial.suggest_int('n_units_l{}'.format(i), 4, 128)
        layers.append(torch.nn.Linear(in_features, out_features))
        layers.append(torch.nn.ReLU())
        in_features = out_features
    layers.append(torch.nn.Linear(in_features, 10))
    layers.append(torch.nn.LogSoftmax(dim=1))
    model = torch.nn.Sequential(*layers).to(torch.device('cpu'))
    ...
    return accuracy

# 3. Create a study object and optimize the objective function.
study = optuna.create_study(direction='maximize')
study.optimize(objective, n_trials=100)

See full example on Github

You can optimize Chainer hyperparameters, such as the number of layers and the number of hidden nodes in each layer, in three steps:

1. Wrap model training with an objective function and return accuracy
2. Suggest hyperparameters using a trial object
3. Create a study object and execute the optimization

import chainer

import optuna

# 1. Define an objective function to be maximized.
def objective(trial):

    # 2. Suggest values of the hyperparameters using a trial object.
    n_layers = trial.suggest_int('n_layers', 1, 3)
    layers = []

    for i in range(n_layers):
        n_units = int(trial.suggest_loguniform('n_units_l{}'.format(i), 4, 128))
        layers.append(L.Linear(None, n_units))
        layers.append(F.relu)
    layers.append(L.Linear(None, 10))

    model = L.Classifier(chainer.Sequential(*layers))
    ...
    return accuracy

# 3. Create a study object and optimize the objective function.
study = optuna.create_study(direction='maximize')
study.optimize(objective, n_trials=100)

See full example on Github

You can optimize TensorFlow hyperparameters, such as the number of layers and the number of hidden nodes in each layer, in three steps:

1. Wrap model training with an objective function and return accuracy
2. Suggest hyperparameters using a trial object
3. Create a study object and execute the optimization

import tensorflow as tf

import optuna

# 1. Define an objective function to be maximized.
def objective(trial):

    # 2. Suggest values of the hyperparameters using a trial object.
    n_layers = trial.suggest_int('n_layers', 1, 3)
    model = tf.keras.Sequential()
    model.add(tf.keras.layers.Flatten())
    for i in range(n_layers):
        num_hidden = int(trial.suggest_loguniform('n_units_l{}'.format(i), 4, 128))
        model.add(tf.keras.layers.Dense(num_hidden, activation='relu'))
    model.add(tf.keras.layers.Dense(CLASSES))
    ...
    return accuracy

# 3. Create a study object and optimize the objective function.
study = optuna.create_study(direction='maximize')
study.optimize(objective, n_trials=100)

See full example on Github

You can optimize Keras hyperparameters, such as the number of filters and kernel size, in three steps:

1. Wrap model training with an objective function and return accuracy
2. Suggest hyperparameters using a trial object
3. Create a study object and execute the optimization

import keras

import optuna

# 1. Define an objective function to be maximized.
def objective(trial):
    model = Sequential()

    # 2. Suggest values of the hyperparameters using a trial object.
    model.add(
        Conv2D(filters=trial.suggest_categorical('filters', [32, 64]),
               kernel_size=trial.suggest_categorical('kernel_size', [3, 5]),
               strides=trial.suggest_categorical('strides', [1, 2]),
               activation=trial.suggest_categorical('activation', ['relu', 'linear']),
               input_shape=input_shape))
    model.add(Flatten())
    model.add(Dense(CLASSES, activation='softmax'))

    # We compile our model with a sampled learning rate.
    lr = trial.suggest_loguniform('lr', 1e-5, 1e-1)
    model.compile(loss='sparse_categorical_crossentropy', optimizer=RMSprop(lr=lr), metrics=['accuracy'])
    ...
    return accuracy

# 3. Create a study object and optimize the objective function.
study = optuna.create_study(direction='maximize')
study.optimize(objective, n_trials=100)

See full example on Github

You can optimize MXNet hyperparameters, such as the number of layers and the number of hidden nodes in each layer, in three steps:

1. Wrap model training with an objective function and return accuracy
2. Suggest hyperparameters using a trial object
3. Create a study object and execute the optimization

import mxnet as mx

import optuna

# 1. Define an objective function to be maximized.
def objective(trial):

    # 2. Suggest values of the hyperparameters using a trial object.
    n_layers = trial.suggest_int('n_layers', 1, 3)

    data = mx.symbol.Variable('data')
    data = mx.sym.flatten(data=data)
    for i in range(n_layers):
        num_hidden = int(trial.suggest_loguniform('n_units_l{}'.format(i), 4, 128))
        data = mx.symbol.FullyConnected(data=data, num_hidden=num_hidden)
        data = mx.symbol.Activation(data=data, act_type="relu")

    data = mx.symbol.FullyConnected(data=data, num_hidden=10)
    mlp = mx.symbol.SoftmaxOutput(data=data, name="softmax")
    ...
    return accuracy

# 3. Create a study object and optimize the objective function.
study = optuna.create_study(direction='maximize')
study.optimize(objective, n_trials=100)

See full example on Github

You can optimize Scikit-Learn hyperparameters, such as the C parameter of SVC and the max_depth of the RandomForestClassifier, in three steps:

1. Wrap model training with an objective function and return accuracy
2. Suggest hyperparameters using a trial object
3. Create a study object and execute the optimization

import sklearn

import optuna

# 1. Define an objective function to be maximized.
def objective(trial):

    # 2. Suggest values for the hyperparameters using a trial object.
    classifier_name = trial.suggest_categorical('classifier', ['SVC', 'RandomForest'])
    if classifier_name == 'SVC':
         svc_c = trial.suggest_loguniform('svc_c', 1e-10, 1e10)
         classifier_obj = sklearn.svm.SVC(C=svc_c, gamma='auto')
    else:
        rf_max_depth = int(trial.suggest_loguniform('rf_max_depth', 2, 32))
        classifier_obj = sklearn.ensemble.RandomForestClassifier(max_depth=rf_max_depth, n_estimators=10)
    ...
    return accuracy

# 3. Create a study object and optimize the objective function.
study = optuna.create_study(direction='maximize')
study.optimize(objective, n_trials=100)

See full example on Github

You can optimize XGBoost hyperparameters, such as the booster type and alpha, in three steps:

1. Wrap model training with an objective function and return accuracy
2. Suggest hyperparameters using a trial object
3. Create a study object and execute the optimization

import xgboost as xgb

import optuna

# 1. Define an objective function to be maximized.
def objective(trial):
    ...

    # 2. Suggest values of the hyperparameters using a trial object.
    param = {
        'silent': 1,
        'objective': 'binary:logistic',
        'booster': trial.suggest_categorical('booster', ['gbtree', 'gblinear', 'dart']),
        'lambda': trial.suggest_loguniform('lambda', 1e-8, 1.0),
        'alpha': trial.suggest_loguniform('alpha', 1e-8, 1.0)
    }

    bst = xgb.train(param, dtrain)
    ...
    return accuracy

# 3. Create a study object and optimize the objective function.
study = optuna.create_study(direction='maximize')
study.optimize(objective, n_trials=100)

See full example on Github

You can optimize LightGBM hyperparameters, such as boosting type and the number of leaves, in three steps:

1. Wrap model training with an objective function and return accuracy
2. Suggest hyperparameters using a trial object
3. Create a study object and execute the optimization

import lightgbm as lgb

import optuna

# 1. Define an objective function to be maximized.
def objective(trial):
    ...

    # 2. Suggest values of the hyperparameters using a trial object.
    param = {
        'objective': 'binary',
        'metric': 'binary_logloss',
        'verbosity': -1,
        'boosting_type': 'gbdt',
        'lambda_l1': trial.suggest_loguniform('lambda_l1', 1e-8, 10.0),
        'lambda_l2': trial.suggest_loguniform('lambda_l2', 1e-8, 10.0),
        'num_leaves': trial.suggest_int('num_leaves', 2, 256),
        'feature_fraction': trial.suggest_uniform('feature_fraction', 0.4, 1.0),
        'bagging_fraction': trial.suggest_uniform('bagging_fraction', 0.4, 1.0),
        'bagging_freq': trial.suggest_int('bagging_freq', 1, 7),
        'min_child_samples': trial.suggest_int('min_child_samples', 5, 100),
    }

    gbm = lgb.train(param, dtrain)
    ...
    return accuracy

# 3. Create a study object and optimize the objective function.
study = optuna.create_study(direction='maximize')
study.optimize(objective, n_trials=100)

See full example on Github

from optuna.visualization import plot_intermediate_values

...
plot_intermediate_values(study)

See full example on Github

% pip install optuna