scikit-learn SGDClassifier熱啟動被忽略了

Question

我正在嘗試使用scikit-learn 0.15.1版本的SGDClassifier。 除了迭代次數之外，似乎沒有任何方法可以設置收斂標准。 因此，我想通過檢查每次迭代時的錯誤，然后熱啟動其他迭代直到改進足夠小來手動執行此操作。

不幸的是，warm_start標志和coef_init / intercept_init似乎都沒有真正熱啟動優化 - 它們似乎都從頭開始。

我該怎么辦？ 如果沒有真正的收斂標准或熱啟動，則分類器不可用。

請注意下面每次重啟時偏差如何增加很多，以及損失如何增加但隨着進一步的迭代而下降。 經過250次迭代后，偏差為-3.44，平均損失為1.46。

sgd = SGDClassifier(loss='log', alpha=alpha, verbose=1, shuffle=True, 
                    warm_start=True)
print('INITIAL FIT')
sgd.fit(X, y, sample_weight=sample_weight)
sgd.n_iter = 1
print('\nONE MORE ITERATION')
sgd.fit(X, y, sample_weight=sample_weight)
sgd.n_iter = 3
print('\nTHREE MORE ITERATIONS')
sgd.fit(X, y, sample_weight=sample_weight)


INITIAL FIT
-- Epoch 1
Norm: 254.11, NNZs: 92299, Bias: -5.239955, T: 122956, Avg. loss: 28.103236
Total training time: 0.04 seconds.
-- Epoch 2
Norm: 138.81, NNZs: 92598, Bias: -5.180938, T: 245912, Avg. loss: 16.420537
Total training time: 0.08 seconds.
-- Epoch 3
Norm: 100.61, NNZs: 92598, Bias: -5.082776, T: 368868, Avg. loss: 12.240537
Total training time: 0.12 seconds.
-- Epoch 4
Norm: 74.18, NNZs: 92598, Bias: -5.076395, T: 491824, Avg. loss: 9.859404
Total training time: 0.17 seconds.
-- Epoch 5
Norm: 55.57, NNZs: 92598, Bias: -5.072369, T: 614780, Avg. loss: 8.280854
Total training time: 0.21 seconds.

ONE MORE ITERATION
-- Epoch 1
Norm: 243.07, NNZs: 92598, Bias: -11.271497, T: 122956, Avg. loss: 26.148746
Total training time: 0.04 seconds.

THREE MORE ITERATIONS
-- Epoch 1
Norm: 258.70, NNZs: 92598, Bias: -16.058395, T: 122956, Avg. loss: 29.666688
Total training time: 0.04 seconds.
-- Epoch 2
Norm: 142.24, NNZs: 92598, Bias: -15.809559, T: 245912, Avg. loss: 17.435114
Total training time: 0.08 seconds.
-- Epoch 3
Norm: 102.71, NNZs: 92598, Bias: -15.715853, T: 368868, Avg. loss: 12.731181
Total training time: 0.12 seconds.

Answer 1

warm_start=True將使用擬合系數作為起點，但重新開始學習率計划。

如果你想手動檢查收斂我建議你使用partial_fit而不是fit作為@AdrienNK建議：

sgd = SGDClassifier(loss='log', alpha=alpha, verbose=1, shuffle=True, 
                warm_start=True, n_iter=1)
sgd.partial_fit(X, y)
# after 1st iteration
sgd.partial_fit(X, y)
# after 2nd iteration
...