动量参数调整（sgd）

from sklearn.datasets import load_digits
from sklearn.neural_network import MLPClassifier
from sklearn.model_selection import train_test_split
from sklearn.metrics import accuracy_score
digits = load_digits()
X = digits.data / 16.0
X_train, X_test, y_train, y_test = train_test_split(X, digits.target, test_size=0.2, random_state=42)
for mom in [0, 0.5, 0.9]:
    clf = MLPClassifier(hidden_layer_sizes=(30,), solver='sgd', learning_rate_init=0.01, momentum=mom, max_iter=500, random_state=42)
    clf.fit(X_train, y_train)
    print(f'momentum={mom}: {accuracy_score(y_test, clf.predict(X_test)):.4f}')