模型训练、评估与推理¶

import paddle

# 指定在 CPU 上训练
paddle.device.set_device('cpu')

# 指定在 GPU 第 0 号卡上训练
# paddle.device.set_device('gpu:0')

CPUPlace

from paddle.vision.transforms import Normalize

transform = Normalize(mean=[127.5], std=[127.5], data_format='CHW')
# 加载 MNIST 训练集和测试集
train_dataset = paddle.vision.datasets.MNIST(mode='train', transform=transform)
test_dataset = paddle.vision.datasets.MNIST(mode='test', transform=transform)

# 模型组网，构建并初始化一个模型 mnist
mnist = paddle.nn.Sequential(
    paddle.nn.Flatten(1, -1), 
    paddle.nn.Linear(784, 512), 
    paddle.nn.ReLU(), 
    paddle.nn.Dropout(0.2), 
    paddle.nn.Linear(512, 10)
)

# 封装模型为一个 model 实例，便于进行后续的训练、评估和推理
model = paddle.Model(mnist)

# 为模型训练做准备，设置优化器及其学习率，并将网络的参数传入优化器，设置损失函数和精度计算方式
model.prepare(optimizer=paddle.optimizer.Adam(learning_rate=0.001, parameters=model.parameters()), 
              loss=paddle.nn.CrossEntropyLoss(), 
              metrics=paddle.metric.Accuracy())

# 启动模型训练，指定训练数据集，设置训练轮次，设置每次数据集计算的批次大小，设置日志格式
model.fit(train_dataset, 
          epochs=5, 
          batch_size=64,
          verbose=1)

The loss value printed in the log is the current step, and the metric is the average value of previous steps.
Epoch 1/5
step  10/938 [..............................] - loss: 0.9679 - acc: 0.4109 - ETA: 13s - 14ms/stepstep 938/938 [==============================] - loss: 0.1158 - acc: 0.9020 - 10ms/step          
Epoch 2/5
step 938/938 [==============================] - loss: 0.0981 - acc: 0.9504 - 10ms/step          
Epoch 3/5
step 938/938 [==============================] - loss: 0.0215 - acc: 0.9588 - 10ms/step          
Epoch 4/5
step 938/938 [==============================] - loss: 0.0134 - acc: 0.9643 - 10ms/step          
Epoch 5/5
step 938/938 [==============================] - loss: 0.3371 - acc: 0.9681 - 11ms/step          

# 用 evaluate 在测试集上对模型进行验证
eval_result = model.evaluate(test_dataset, verbose=1)
print(eval_result)

Eval begin...
step 10000/10000 [==============================] - loss: 2.3842e-07 - acc: 0.9714 - 2ms/step          
Eval samples: 10000
{'loss': [2.384186e-07], 'acc': 0.9714}

# 用 predict 在测试集上对模型进行推理
test_result = model.predict(test_dataset)
# 由于模型是单一输出，test_result的形状为[1, 10000]，10000是测试数据集的数据量。这里打印第一个数据的结果，这个数组表示每个数字的预测概率
print(len(test_result))
print(test_result[0][0])

# 从测试集中取出一张图片
img, label = test_dataset[0]

# 打印推理结果，这里的argmax函数用于取出预测值中概率最高的一个的下标，作为预测标签
pred_label = test_result[0][0].argmax()
print('true label: {}, pred label: {}'.format(label[0], pred_label))
# 使用matplotlib库，可视化图片
from matplotlib import pyplot as plt
plt.imshow(img[0])

Predict begin...
step 10000/10000 [==============================] - 2ms/step          
Predict samples: 10000
1
[[ -6.512169   -6.7076845   0.5048795   1.6733919  -9.670526   -1.6352568
  -15.833721   13.87411    -8.215239    1.5966017]]
true label: 7, pred label: 7





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# dataset与mnist的定义与使用高层API的内容一致
# 用 DataLoader 实现数据加载
train_loader = paddle.io.DataLoader(train_dataset, batch_size=64, shuffle=True)

# 将mnist模型及其所有子层设置为训练模式。这只会影响某些模块，如Dropout和BatchNorm。
mnist.train()

# 设置迭代次数
epochs = 5

# 设置优化器
optim = paddle.optimizer.Adam(parameters=mnist.parameters())
# 设置损失函数
loss_fn = paddle.nn.CrossEntropyLoss()
for epoch in range(epochs):
    for batch_id, data in enumerate(train_loader()):
        
        x_data = data[0]            # 训练数据
        y_data = data[1]            # 训练数据标签
        predicts = mnist(x_data)    # 预测结果  
        
        # 计算损失 等价于 prepare 中loss的设置
        loss = loss_fn(predicts, y_data)
        
        # 计算准确率 等价于 prepare 中metrics的设置
        acc = paddle.metric.accuracy(predicts, y_data)
        
        # 下面的反向传播、打印训练信息、更新参数、梯度清零都被封装到 Model.fit() 中
        # 反向传播 
        loss.backward()
        
        if (batch_id+1) % 900 == 0:
            print("epoch: {}, batch_id: {}, loss is: {}, acc is: {}".format(epoch, batch_id+1, loss.numpy(), acc.numpy()))
        # 更新参数 
        optim.step()
        # 梯度清零
        optim.clear_grad()

epoch: 0, batch_id: 900, loss is: [0.06991791], acc is: [0.96875]
epoch: 1, batch_id: 900, loss is: [0.02878829], acc is: [1.]
epoch: 2, batch_id: 900, loss is: [0.07192856], acc is: [0.96875]
epoch: 3, batch_id: 900, loss is: [0.20411499], acc is: [0.96875]
epoch: 4, batch_id: 900, loss is: [0.13589518], acc is: [0.96875]

# 加载测试数据集
test_loader = paddle.io.DataLoader(test_dataset, batch_size=64, drop_last=True)
# 设置损失函数
loss_fn = paddle.nn.CrossEntropyLoss()
# 将该模型及其所有子层设置为预测模式。这只会影响某些模块，如Dropout和BatchNorm
mnist.eval()
# 禁用动态图梯度计算
for batch_id, data in enumerate(test_loader()):
    
    x_data = data[0]            # 测试数据
    y_data = data[1]            # 测试数据标签
    predicts = mnist(x_data)    # 预测结果
    
    # 计算损失与精度
    loss = loss_fn(predicts, y_data)
    acc = paddle.metric.accuracy(predicts, y_data)
    
    # 打印信息
    if (batch_id+1) % 30 == 0:
        print("batch_id: {}, loss is: {}, acc is: {}".format(batch_id+1, loss.numpy(), acc.numpy()))

batch_id: 30, loss is: [0.23106411], acc is: [0.953125]
batch_id: 60, loss is: [0.4329119], acc is: [0.90625]
batch_id: 90, loss is: [0.07333981], acc is: [0.96875]
batch_id: 120, loss is: [0.00324837], acc is: [1.]
batch_id: 150, loss is: [0.0857158], acc is: [0.96875]

# 加载测试数据集
test_loader = paddle.io.DataLoader(test_dataset, batch_size=64, drop_last=True)
# 将该模型及其所有子层设置为预测模式
mnist.eval()
for batch_id, data in enumerate(test_loader()):
    # 取出测试数据
    x_data = data[0] 
    # 获取预测结果
    predicts = mnist(x_data)
print("predict finished")

# 从测试集中取出一组数据
img, label = test_loader().next()

# 执行推理并打印结果
pred_label = mnist(img)[0].argmax()
print('true label: {}, pred label: {}'.format(label[0].item(), pred_label[0].item()))
# 可视化图片
from matplotlib import pyplot as plt
plt.imshow(img[0][0])

predict finished
true label: 7, pred label: 7





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