加载经过训练的Keras模型并继续训练

问题:加载经过训练的Keras模型并继续训练

我想知道是否有可能保存经过部分训练的Keras模型并在再次加载模型后继续进行训练。

这样做的原因是,将来我将拥有更多的训练数据,并且我不想再次对整个模型进行训练。

我正在使用的功能是:

#Partly train model
model.fit(first_training, first_classes, batch_size=32, nb_epoch=20)

#Save partly trained model
model.save('partly_trained.h5')

#Load partly trained model
from keras.models import load_model
model = load_model('partly_trained.h5')

#Continue training
model.fit(second_training, second_classes, batch_size=32, nb_epoch=20)

编辑1:添加了完全正常的示例

对于第10个时期后的第一个数据集,最后一个时期的损失将为0.0748,精度为0.9863。

保存,删除和重新加载模型后,第二个数据集上训练的模型的损失和准确性分别为0.1711和0.9504。

这是由新的训练数据还是完全重新训练的模型引起的?

"""
Model by: http://machinelearningmastery.com/
"""
# load (downloaded if needed) the MNIST dataset
import numpy
from keras.datasets import mnist
from keras.models import Sequential
from keras.layers import Dense
from keras.utils import np_utils
from keras.models import load_model
numpy.random.seed(7)

def baseline_model():
    model = Sequential()
    model.add(Dense(num_pixels, input_dim=num_pixels, init='normal', activation='relu'))
    model.add(Dense(num_classes, init='normal', activation='softmax'))
    model.compile(loss='categorical_crossentropy', optimizer='adam', metrics=['accuracy'])
    return model

if __name__ == '__main__':
    # load data
    (X_train, y_train), (X_test, y_test) = mnist.load_data()

    # flatten 28*28 images to a 784 vector for each image
    num_pixels = X_train.shape[1] * X_train.shape[2]
    X_train = X_train.reshape(X_train.shape[0], num_pixels).astype('float32')
    X_test = X_test.reshape(X_test.shape[0], num_pixels).astype('float32')
    # normalize inputs from 0-255 to 0-1
    X_train = X_train / 255
    X_test = X_test / 255
    # one hot encode outputs
    y_train = np_utils.to_categorical(y_train)
    y_test = np_utils.to_categorical(y_test)
    num_classes = y_test.shape[1]

    # build the model
    model = baseline_model()

    #Partly train model
    dataset1_x = X_train[:3000]
    dataset1_y = y_train[:3000]
    model.fit(dataset1_x, dataset1_y, nb_epoch=10, batch_size=200, verbose=2)

    # Final evaluation of the model
    scores = model.evaluate(X_test, y_test, verbose=0)
    print("Baseline Error: %.2f%%" % (100-scores[1]*100))

    #Save partly trained model
    model.save('partly_trained.h5')
    del model

    #Reload model
    model = load_model('partly_trained.h5')

    #Continue training
    dataset2_x = X_train[3000:]
    dataset2_y = y_train[3000:]
    model.fit(dataset2_x, dataset2_y, nb_epoch=10, batch_size=200, verbose=2)
    scores = model.evaluate(X_test, y_test, verbose=0)
    print("Baseline Error: %.2f%%" % (100-scores[1]*100))

I was wondering if it was possible to save a partly trained Keras model and continue the training after loading the model again.

The reason for this is that I will have more training data in the future and I do not want to retrain the whole model again.

The functions which I am using are:

#Partly train model
model.fit(first_training, first_classes, batch_size=32, nb_epoch=20)

#Save partly trained model
model.save('partly_trained.h5')

#Load partly trained model
from keras.models import load_model
model = load_model('partly_trained.h5')

#Continue training
model.fit(second_training, second_classes, batch_size=32, nb_epoch=20)

Edit 1: added fully working example

With the first dataset after 10 epochs the loss of the last epoch will be 0.0748 and the accuracy 0.9863.

After saving, deleting and reloading the model the loss and accuracy of the model trained on the second dataset will be 0.1711 and 0.9504 respectively.

Is this caused by the new training data or by a completely re-trained model?

"""
Model by: http://machinelearningmastery.com/
"""
# load (downloaded if needed) the MNIST dataset
import numpy
from keras.datasets import mnist
from keras.models import Sequential
from keras.layers import Dense
from keras.utils import np_utils
from keras.models import load_model
numpy.random.seed(7)

def baseline_model():
    model = Sequential()
    model.add(Dense(num_pixels, input_dim=num_pixels, init='normal', activation='relu'))
    model.add(Dense(num_classes, init='normal', activation='softmax'))
    model.compile(loss='categorical_crossentropy', optimizer='adam', metrics=['accuracy'])
    return model

if __name__ == '__main__':
    # load data
    (X_train, y_train), (X_test, y_test) = mnist.load_data()

    # flatten 28*28 images to a 784 vector for each image
    num_pixels = X_train.shape[1] * X_train.shape[2]
    X_train = X_train.reshape(X_train.shape[0], num_pixels).astype('float32')
    X_test = X_test.reshape(X_test.shape[0], num_pixels).astype('float32')
    # normalize inputs from 0-255 to 0-1
    X_train = X_train / 255
    X_test = X_test / 255
    # one hot encode outputs
    y_train = np_utils.to_categorical(y_train)
    y_test = np_utils.to_categorical(y_test)
    num_classes = y_test.shape[1]

    # build the model
    model = baseline_model()

    #Partly train model
    dataset1_x = X_train[:3000]
    dataset1_y = y_train[:3000]
    model.fit(dataset1_x, dataset1_y, nb_epoch=10, batch_size=200, verbose=2)

    # Final evaluation of the model
    scores = model.evaluate(X_test, y_test, verbose=0)
    print("Baseline Error: %.2f%%" % (100-scores[1]*100))

    #Save partly trained model
    model.save('partly_trained.h5')
    del model

    #Reload model
    model = load_model('partly_trained.h5')

    #Continue training
    dataset2_x = X_train[3000:]
    dataset2_y = y_train[3000:]
    model.fit(dataset2_x, dataset2_y, nb_epoch=10, batch_size=200, verbose=2)
    scores = model.evaluate(X_test, y_test, verbose=0)
    print("Baseline Error: %.2f%%" % (100-scores[1]*100))

回答 0

实际上- model.save根据您的情况保存重新开始培训所需的所有信息。重新加载模型可能会破坏的唯一事情是优化器状态。要进行检查-尝试save重新加载模型并根据训练数据进行训练。

Actually – model.save saves all information need for restarting training in your case. The only thing which could be spoiled by reloading model is your optimizer state. To check that – try to save and reload model and train it on training data.


回答 1

问题可能是您使用了不同的优化器-或优化器使用了不同的参数。我只是在使用自定义预训练模型时遇到了相同的问题

reduce_lr = ReduceLROnPlateau(monitor='loss', factor=lr_reduction_factor,
                              patience=patience, min_lr=min_lr, verbose=1)

对于预训练模型,其中原始学习率从0.0003开始,在预训练过程中,原始学习率降低为min_learning率,即0.000003

我只是将该行复制到使用预训练模型的脚本中,并且准确性很差。直到我注意到预训练模型的最后学习率是最小学习率,即0.000003。如果我以该学习率开始,那么我得到的精确度与预训练模型的输出完全相同-这是有道理的,因为它的学习率是预训练模型中最后一次使用的学习率的100倍该模型将导致GD严重超调,从而导致精度大大降低。

The problem might be that you use a different optimizer – or different arguments to your optimizer. I just had the same issue with a custom pretrained model, using

reduce_lr = ReduceLROnPlateau(monitor='loss', factor=lr_reduction_factor,
                              patience=patience, min_lr=min_lr, verbose=1)

for the pretrained model, whereby the original learning rate starts at 0.0003 and during pre-training it is reduced to the min_learning rate, which is 0.000003

I just copied that line over to the script which uses the pre-trained model and got really bad accuracies. Until I noticed that the last learning rate of the pretrained model was the min learning rate, i.e. 0.000003. And if I start with that learning rate, I get exactly the same accuracies to start with as the output of the pretrained model – which makes sense, as starting with a learning rate that is 100 times bigger than the last learning rate used in the pretrained model will result in a huge overshoot of GD and hence in heavily decreased accuracies.


回答 2

以上大多数答案都涵盖了重点。如果您正在使用最新的Tensorflow(TF2.1或更高版本),则以下示例将为您提供帮助。该代码的模型部分来自Tensorflow网站。

import tensorflow as tf
from tensorflow import keras
mnist = tf.keras.datasets.mnist

(x_train, y_train),(x_test, y_test) = mnist.load_data()
x_train, x_test = x_train / 255.0, x_test / 255.0

def create_model():
  model = tf.keras.models.Sequential([
    tf.keras.layers.Flatten(input_shape=(28, 28)),
    tf.keras.layers.Dense(512, activation=tf.nn.relu),  
    tf.keras.layers.Dropout(0.2),
    tf.keras.layers.Dense(10, activation=tf.nn.softmax)
    ])

  model.compile(optimizer='adam', loss='sparse_categorical_crossentropy',metrics=['accuracy'])
  return model

# Create a basic model instance
model=create_model()
model.fit(x_train, y_train, epochs = 10, validation_data = (x_test,y_test),verbose=1)

请以* .tf格式保存模型。根据我的经验,如果您定义了任何custom_loss,*。h5格式将不会保存优化器状态,​​因此如果您要从我们离开的地方重新训练模型,将无法达到您的目的。

# saving the model in tensorflow format
model.save('./MyModel_tf',save_format='tf')


# loading the saved model
loaded_model = tf.keras.models.load_model('./MyModel_tf')

# retraining the model
loaded_model.fit(x_train, y_train, epochs = 10, validation_data = (x_test,y_test),verbose=1)

这种方法将在保存模型之前重新开始训练。正如其他人所提到的,如果你想保存最好的模型的重量或要保存模型的加权每次你需要使用keras回调函数(ModelCheckpoint)的选项,如时代save_weights_only=Truesave_freq='epoch'save_best_only

有关更多详细信息,请在此处检查在此处查看另一个示例。

Most of the above answers covered important points. If you are using recent Tensorflow (TF2.1 or above), Then the following example will help you. The model part of the code is from Tensorflow website.

import tensorflow as tf
from tensorflow import keras
mnist = tf.keras.datasets.mnist

(x_train, y_train),(x_test, y_test) = mnist.load_data()
x_train, x_test = x_train / 255.0, x_test / 255.0

def create_model():
  model = tf.keras.models.Sequential([
    tf.keras.layers.Flatten(input_shape=(28, 28)),
    tf.keras.layers.Dense(512, activation=tf.nn.relu),  
    tf.keras.layers.Dropout(0.2),
    tf.keras.layers.Dense(10, activation=tf.nn.softmax)
    ])

  model.compile(optimizer='adam', loss='sparse_categorical_crossentropy',metrics=['accuracy'])
  return model

# Create a basic model instance
model=create_model()
model.fit(x_train, y_train, epochs = 10, validation_data = (x_test,y_test),verbose=1)

Please save the model in *.tf format. From my experience, if you have any custom_loss defined, *.h5 format will not save optimizer status and hence will not serve your purpose if you want to retrain the model from where we left.

# saving the model in tensorflow format
model.save('./MyModel_tf',save_format='tf')


# loading the saved model
loaded_model = tf.keras.models.load_model('./MyModel_tf')

# retraining the model
loaded_model.fit(x_train, y_train, epochs = 10, validation_data = (x_test,y_test),verbose=1)

This approach will restart the training where we left before saving the model. As mentioned by others, if you want to save weights of best model or you want to save weights of model every epoch you need to use keras callbacks function (ModelCheckpoint) with options such as save_weights_only=True, save_freq='epoch', and save_best_only.

For more details, please check here and another example here.


回答 3

注意,Keras有时在加载的模型上有问题,如此处所示。这可能会解释一些情况,其中您并非从相同的训练准确性开始。

Notice that Keras sometimes has issues with loaded models, as in here. This might explain cases in which you don’t start from the same trained accuracy.


回答 4

所有上述帮助,保存模型和权重后,您必须从与LR相同的学习rate()中恢复。直接在优化器上进行设置。

请注意,由于模型可能已达到局部最小值(可能是全局最小值),因此无法保证从那里得到改善。除非您打算以受控方式提高学习率并将模型推向不远处的可能更好的最小值,否则没有必要恢复模型以搜索另一个局部最小值。

All above helps, you must resume from same learning rate() as the LR when the model and weights were saved. Set it directly on the optimizer.

Note that improvement from there is not guaranteed, because the model may have reached the local minimum, which may be global. There is no point to resume a model in order to search for another local minimum, unless you intent to increase the learning rate in a controlled fashion and nudge the model into a possibly better minimum not far away.


回答 5

您可能还遇到了概念漂移问题,请参阅在有新观测值时是否应重新训练模型。还有一些学术论文讨论的灾难性遗忘的概念。这是与MNIST一起进行的灾难性遗忘的实证研究

You might also be hitting Concept Drift, see Should you retrain a model when new observations are available. There’s also the concept of catastrophic forgetting which a bunch of academic papers discuss. Here’s one with MNIST Empirical investigation of catastrophic forgetting