在 PyTorch 中使用逻辑回归识别手写数字
逻辑回归是一种非常常用的统计方法,它允许我们从一组自变量中预测二进制输出。本文之前已经介绍了逻辑回归的各种属性及其Python实现。现在,我们将了解如何在 PyTorch 中实现这一点,PyTorch 是 Facebook 正在开发的一个非常流行的深度学习库。
现在,我们将了解如何使用 PyTorch 中的逻辑回归对 MNIST 数据集中的手写数字进行分类。首先,您需要将 PyTorch 安装到您的Python环境中。最简单的方法是使用 pip 或 conda 工具。访问 pytorch.org 并安装您想要使用的Python解释器和包管理器的版本。
安装 PyTorch 后,现在让我们看一下代码。编写下面给出的三行以导入所需的库函数和对象。
Python3
import torch
import torch.nn as nn
import torchvision.datasets as dsets
import torchvision.transforms as transforms
from torch.autograd import Variable
Python3
# MNIST Dataset (Images and Labels)
train_dataset = dsets.MNIST(root ='./data',
train = True,
transform = transforms.ToTensor(),
download = True)
test_dataset = dsets.MNIST(root ='./data',
train = False,
transform = transforms.ToTensor())
# Dataset Loader (Input Pipeline)
train_loader = torch.utils.data.DataLoader(dataset = train_dataset,
batch_size = batch_size,
shuffle = True)
test_loader = torch.utils.data.DataLoader(dataset = test_dataset,
batch_size = batch_size,
shuffle = False)
Python3
# Hyper Parameters
input_size = 784
num_classes = 10
num_epochs = 5
batch_size = 100
learning_rate = 0.001
Python3
class LogisticRegression(nn.Module):
def __init__(self, input_size, num_classes):
super(LogisticRegression, self).__init__()
self.linear = nn.Linear(input_size, num_classes)
def forward(self, x):
out = self.linear(x)
return out
Python3
model = LogisticRegression(input_size, num_classes)
Python3
criterion = nn.CrossEntropyLoss()
optimizer = torch.optim.SGD(model.parameters(), lr = learning_rate)
Python3
# Training the Model
for epoch in range(num_epochs):
for i, (images, labels) in enumerate(train_loader):
images = Variable(images.view(-1, 28 * 28))
labels = Variable(labels)
# Forward + Backward + Optimize
optimizer.zero_grad()
outputs = model(images)
loss = criterion(outputs, labels)
loss.backward()
optimizer.step()
if (i + 1) % 100 == 0:
print('Epoch: [% d/% d], Step: [% d/% d], Loss: %.4f'
% (epoch + 1, num_epochs, i + 1,
len(train_dataset) // batch_size, loss.data[0]))
Python3
# Test the Model
correct = 0
total = 0
for images, labels in test_loader:
images = Variable(images.view(-1, 28 * 28))
outputs = model(images)
_, predicted = torch.max(outputs.data, 1)
total += labels.size(0)
correct += (predicted == labels).sum()
print('Accuracy of the model on the 10000 test images: % d %%' % (
100 * correct / total))
Python3
import torch
import torch.nn as nn
import torchvision.datasets as dsets
import torchvision.transforms as transforms
from torch.autograd import Variable
# MNIST Dataset (Images and Labels)
train_dataset = dsets.MNIST(root ='./data',
train = True,
transform = transforms.ToTensor(),
download = True)
test_dataset = dsets.MNIST(root ='./data',
train = False,
transform = transforms.ToTensor())
# Dataset Loader (Input Pipeline)
train_loader = torch.utils.data.DataLoader(dataset = train_dataset,
batch_size = batch_size,
shuffle = True)
test_loader = torch.utils.data.DataLoader(dataset = test_dataset,
batch_size = batch_size,
shuffle = False)
# Hyper Parameters
input_size = 784
num_classes = 10
num_epochs = 5
batch_size = 100
learning_rate = 0.001
# Model
class LogisticRegression(nn.Module):
def __init__(self, input_size, num_classes):
super(LogisticRegression, self).__init__()
self.linear = nn.Linear(input_size, num_classes)
def forward(self, x):
out = self.linear(x)
return out
model = LogisticRegression(input_size, num_classes)
# Loss and Optimizer
# Softmax is internally computed.
# Set parameters to be updated.
criterion = nn.CrossEntropyLoss()
optimizer = torch.optim.SGD(model.parameters(), lr = learning_rate)
# Training the Model
for epoch in range(num_epochs):
for i, (images, labels) in enumerate(train_loader):
images = Variable(images.view(-1, 28 * 28))
labels = Variable(labels)
# Forward + Backward + Optimize
optimizer.zero_grad()
outputs = model(images)
loss = criterion(outputs, labels)
loss.backward()
optimizer.step()
if (i + 1) % 100 == 0:
print('Epoch: [% d/% d], Step: [% d/% d], Loss: %.4f'
% (epoch + 1, num_epochs, i + 1,
len(train_dataset) // batch_size, loss.data[0]))
# Test the Model
correct = 0
total = 0
for images, labels in test_loader:
images = Variable(images.view(-1, 28 * 28))
outputs = model(images)
_, predicted = torch.max(outputs.data, 1)
total += labels.size(0)
correct += (predicted == labels).sum()
print('Accuracy of the model on the 10000 test images: % d %%' % (
100 * correct / total))
这里, torch.nn模块包含模型所需的代码, torchvision.datasets包含 MNIST 数据集。它包含我们将在这里使用的手写数字数据集。 torchvision.transforms模块包含将对象转换为其他对象的各种方法。在这里,我们将使用它从图像转换为 PyTorch 张量。此外, torch.autograd模块包含变量类等,我们将在定义我们的张量时使用它。
接下来,我们将下载数据集并将其加载到内存中。
Python3
# MNIST Dataset (Images and Labels)
train_dataset = dsets.MNIST(root ='./data',
train = True,
transform = transforms.ToTensor(),
download = True)
test_dataset = dsets.MNIST(root ='./data',
train = False,
transform = transforms.ToTensor())
# Dataset Loader (Input Pipeline)
train_loader = torch.utils.data.DataLoader(dataset = train_dataset,
batch_size = batch_size,
shuffle = True)
test_loader = torch.utils.data.DataLoader(dataset = test_dataset,
batch_size = batch_size,
shuffle = False)
现在,我们将定义我们的超参数。
Python3
# Hyper Parameters
input_size = 784
num_classes = 10
num_epochs = 5
batch_size = 100
learning_rate = 0.001
在我们的数据集中,图像大小为 28*28。因此,我们的输入大小为 784。此外,其中存在 10 个数字,因此我们可以有 10 个不同的输出。因此,我们将 num_classes 设置为 10。此外,我们将在整个数据集上训练五次。最后,我们将小批量训练,每组 100 张图像,以防止由于内存溢出导致程序崩溃。
在此之后,我们将定义我们的模型如下。在这里,我们将我们的模型初始化为torch.nn.Module的子类,然后定义前向传递。在我们正在编写的代码中,softmax 是在每次前向传递期间内部计算的,因此我们不需要在 forward()函数中指定它。
Python3
class LogisticRegression(nn.Module):
def __init__(self, input_size, num_classes):
super(LogisticRegression, self).__init__()
self.linear = nn.Linear(input_size, num_classes)
def forward(self, x):
out = self.linear(x)
return out
定义了我们的类之后,现在我们为它实例化一个对象。
Python3
model = LogisticRegression(input_size, num_classes)
接下来,我们设置损失函数和优化器。在这里,我们将使用交叉熵损失,对于优化器,我们将使用随机梯度下降算法,学习率为 0.001,如上面的超参数中所定义。
Python3
criterion = nn.CrossEntropyLoss()
optimizer = torch.optim.SGD(model.parameters(), lr = learning_rate)
现在,我们要开始训练了。在这里,我们将执行以下任务:
- 将所有渐变重置为 0。
- 向前传球。
- 计算损失。
- 执行反向传播。
- 更新所有权重。
Python3
# Training the Model
for epoch in range(num_epochs):
for i, (images, labels) in enumerate(train_loader):
images = Variable(images.view(-1, 28 * 28))
labels = Variable(labels)
# Forward + Backward + Optimize
optimizer.zero_grad()
outputs = model(images)
loss = criterion(outputs, labels)
loss.backward()
optimizer.step()
if (i + 1) % 100 == 0:
print('Epoch: [% d/% d], Step: [% d/% d], Loss: %.4f'
% (epoch + 1, num_epochs, i + 1,
len(train_dataset) // batch_size, loss.data[0]))
最后,我们将使用以下代码测试模型。
Python3
# Test the Model
correct = 0
total = 0
for images, labels in test_loader:
images = Variable(images.view(-1, 28 * 28))
outputs = model(images)
_, predicted = torch.max(outputs.data, 1)
total += labels.size(0)
correct += (predicted == labels).sum()
print('Accuracy of the model on the 10000 test images: % d %%' % (
100 * correct / total))
假设您正确执行了所有步骤,您将获得 82% 的准确率,这与当今使用特殊类型神经网络架构的最先进模型相去甚远。供您参考,您可以在下面找到本文的完整代码:
Python3
import torch
import torch.nn as nn
import torchvision.datasets as dsets
import torchvision.transforms as transforms
from torch.autograd import Variable
# MNIST Dataset (Images and Labels)
train_dataset = dsets.MNIST(root ='./data',
train = True,
transform = transforms.ToTensor(),
download = True)
test_dataset = dsets.MNIST(root ='./data',
train = False,
transform = transforms.ToTensor())
# Dataset Loader (Input Pipeline)
train_loader = torch.utils.data.DataLoader(dataset = train_dataset,
batch_size = batch_size,
shuffle = True)
test_loader = torch.utils.data.DataLoader(dataset = test_dataset,
batch_size = batch_size,
shuffle = False)
# Hyper Parameters
input_size = 784
num_classes = 10
num_epochs = 5
batch_size = 100
learning_rate = 0.001
# Model
class LogisticRegression(nn.Module):
def __init__(self, input_size, num_classes):
super(LogisticRegression, self).__init__()
self.linear = nn.Linear(input_size, num_classes)
def forward(self, x):
out = self.linear(x)
return out
model = LogisticRegression(input_size, num_classes)
# Loss and Optimizer
# Softmax is internally computed.
# Set parameters to be updated.
criterion = nn.CrossEntropyLoss()
optimizer = torch.optim.SGD(model.parameters(), lr = learning_rate)
# Training the Model
for epoch in range(num_epochs):
for i, (images, labels) in enumerate(train_loader):
images = Variable(images.view(-1, 28 * 28))
labels = Variable(labels)
# Forward + Backward + Optimize
optimizer.zero_grad()
outputs = model(images)
loss = criterion(outputs, labels)
loss.backward()
optimizer.step()
if (i + 1) % 100 == 0:
print('Epoch: [% d/% d], Step: [% d/% d], Loss: %.4f'
% (epoch + 1, num_epochs, i + 1,
len(train_dataset) // batch_size, loss.data[0]))
# Test the Model
correct = 0
total = 0
for images, labels in test_loader:
images = Variable(images.view(-1, 28 * 28))
outputs = model(images)
_, predicted = torch.max(outputs.data, 1)
total += labels.size(0)
correct += (predicted == labels).sum()
print('Accuracy of the model on the 10000 test images: % d %%' % (
100 * correct / total))
参考资料:
- PyTorchZeroToAll
- 云杰在 Github