# 定义训练方法 sgd = SGD(lr=0.1) model.compile(loss='binary_crossentropy', optimizer=sgd, metrics=['accuracy'])
时间: 2024-01-20 22:02:47 浏览: 26
这段代码定义了BP神经网络的训练方法。
- `sgd = SGD(lr=0.1)`:定义随机梯度下降法(SGD)优化器,其中`lr`为学习率,控制着网络权重的更新步长。
- `model.compile(loss='binary_crossentropy', optimizer=sgd, metrics=['accuracy'])`:编译模型,指定损失函数为交叉熵,优化器为SGD,评估指标为准确率。
这样就为BP神经网络的训练做好了准备。在使用`fit`函数进行训练时,模型会根据训练数据和损失函数计算出每个权重的梯度,并使用SGD优化器对权重进行更新,以最小化损失函数。
相关问题
opt = keras.optimizers.Adam(learning_rate=0.001) model.compile(loss = 'binary_crossentropy', optimizer = opt,metrics=METRICS) # 编译模型。由于我们做的是二元分类,所以我们指定损失函数为binary_crossentropy,以及模式为binary # 另外常见的损失函数还有mean_squared_error、categorical_crossentropy等,请阅读帮助文件。 # 求解方法我们指定用adam,还有sgd、rmsprop等可选 history_NN=model.fit(x_train.values, y_train.values, epochs = 200, batch_size = 128,validation_split=0.1)
这段代码是对上面建立的神经网络模型进行编译和训练。首先指定优化器为Adam,学习率为0.001,然后指定损失函数为binary_crossentropy,并且使用模型的accuracy评估模型的性能。接着通过调用fit方法对模型进行训练,训练数据为x_train和y_train,训练轮数为200,每个batch包含128个样本。此外,还指定了一个validation_split参数,用于将训练集中的一部分数据作为验证集来检验模型的性能。
训练完成后,模型的性能可以通过history_NN对象来查看,例如loss曲线、accuracy曲线等。
from keras import applications from keras.preprocessing.image import ImageDataGenerator from keras import optimizers from keras.models import Sequential, Model from keras.layers import Dropout, Flatten, Dense img_width, img_height = 256, 256 batch_size = 16 epochs = 50 train_data_dir = 'C:/Users/Z-/Desktop/kaggle/train' validation_data_dir = 'C:/Users/Z-/Desktop/kaggle/test1' OUT_CATAGORIES = 1 nb_train_samples = 2000 nb_validation_samples = 100 base_model = applications.VGG16(weights='imagenet', include_top=False, input_shape=(img_width, img_height, 3)) base_model.summary() for layer in base_model.layers[:15]: layer.trainable = False top_model = Sequential() top_model.add(Flatten(input_shape=base_model.output_shape[1:])) top_model.add(Dense(256, activation='relu')) top_model.add(Dropout(0.5)) top_model.add(Dense(OUT_CATAGORIES, activation='sigmoid')) model = Model(inputs=base_model.input, outputs=top_model(base_model.output)) model.compile(loss='binary_crossentropy', optimizer=optimizers.SGD(learning_rate=0.0001, momentum=0.9), metrics=['accuracy']) train_datagen = ImageDataGenerator(rescale=1. / 255, horizontal_flip=True) test_datagen = ImageDataGenerator(rescale=1. / 255) train_generator = train_datagen.flow_from_directory( train_data_dir, target_size=(img_height, img_width), batch_size=batch_size, class_mode='binary') validation_generator = test_datagen.flow_from_directory( validation_data_dir, target_size=(img_height, img_width), batch_size=batch_size, class_mode='binary', shuffle=False ) model.fit_generator( train_generator, steps_per_epoch=nb_train_samples / batch_size, epochs=epochs, validation_data=validation_generator, validation_steps=nb_validation_samples / batch_size, verbose=2, workers=12 ) score = model.evaluate_generator(validation_generator, nb_validation_samples / batch_size) scores = model.predict_generator(validation_generator, nb_validation_samples / batch_size)看看这段代码有什么错误
在段代码中,有一些错误和需要注意的地方:
1. `img_width` 和 `img_height` 变量没有被定义,需要先定义它们的值。
2. `OUT_CATAGORIES` 变量也没有被定义,需要给它赋值。
3. 在使用 `train_generator` 和 `validation_generator` 时,`steps_per_epoch` 和 `validation_steps` 应该为整数值,而不是浮点数。可以使用 `//` 运算符来进行整除操作。
4. 在评估模型的性能时,`evaluate_generator` 和 `predict_generator` 方法的参数应该是整数值,而不是浮点数。可以使用 `int()` 函数来将浮点数转换为整数。
下面是修改后的代码:
```python
from keras import applications
from keras.preprocessing.image import ImageDataGenerator
from keras import optimizers
from keras.models import Sequential, Model
from keras.layers import Dropout, Flatten, Dense
img_width, img_height = 256, 256
batch_size = 16
epochs = 50
train_data_dir = 'C:/Users/Z-/Desktop/kaggle/train'
validation_data_dir = 'C:/Users/Z-/Desktop/kaggle/test1'
OUT_CATAGORIES = 1
nb_train_samples = 2000
nb_validation_samples = 100
base_model = applications.VGG16(weights='imagenet',
include_top=False,
input_shape=(img_width, img_height, 3))
base_model.summary()
for layer in base_model.layers[:15]:
layer.trainable = False
top_model = Sequential()
top_model.add(Flatten(input_shape=base_model.output_shape[1:]))
top_model.add(Dense(256, activation='relu'))
top_model.add(Dropout(0.5))
top_model.add(Dense(OUT_CATAGORIES, activation='sigmoid'))
model = Model(inputs=base_model.input,
outputs=top_model(base_model.output))
model.compile(loss='binary_crossentropy',
optimizer=optimizers.SGD(learning_rate=0.0001, momentum=0.9),
metrics=['accuracy'])
train_datagen = ImageDataGenerator(rescale=1. / 255,
horizontal_flip=True)
test_datagen = ImageDataGenerator(rescale=1. / 255)
train_generator = train_datagen.flow_from_directory(
train_data_dir,
target_size=(img_height, img_width),
batch_size=batch_size,
class_mode='binary')
validation_generator = test_datagen.flow_from_directory(
validation_data_dir,
target_size=(img_height, img_width),
batch_size=batch_size,
class_mode='binary',
shuffle=False)
model.fit_generator(
train_generator,
steps_per_epoch=nb_train_samples // batch_size,
epochs=epochs,
validation_data=validation_generator,
validation_steps=nb_validation_samples // batch_size,
verbose=2,
workers=12)
score = model.evaluate_generator(validation_generator, int(nb_validation_samples / batch_size))
scores = model.predict_generator(validation_generator, int(nb_validation_samples / batch_size))
```