hello-python/torch_test/logistic_regression.py

import torch
from torch.autograd import Variable
from torch import nn, optim
import torchvision.transforms as transforms
import torchvision.datasets as dsets
import numpy as np
from skorch import NeuralNet
from skorch.callbacks import EpochScoring
from matplotlib import pyplot as plt

from spacecutter.callbacks import AscensionCallback
from spacecutter.losses import CumulativeLinkLoss
from spacecutter.models import OrdinalLogisticModel

class LogisticRegression(nn.Module):
    def __init__(self, input_dim, output_dim):
        super(LogisticRegression, self).__init__()
        self.linear = nn.Linear(input_dim, output_dim)

    def forward(self, x):
        outputs = self.linear(x)
        return outputs

def regression_on_mnist():
    batch_size = 100
    n_iters = 5000
    input_dim = 784
    output_dim = 10
    lr_rate = 0.001

    train_dataset = dsets.MNIST(root='./torch_test/data', train=True, transform=transforms.ToTensor(), download=False)
    test_dataset = dsets.MNIST(root='./torch_test/data', train=False, transform=transforms.ToTensor())

    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)

    model = LogisticRegression(input_dim, output_dim)
    criterion = nn.CrossEntropyLoss() # 计算 softmax 分布之上的交叉熵损失
    optimizer = optim.SGD(model.parameters(), lr=lr_rate)

    epochs = n_iters / (len(train_dataset) / batch_size)
    iter = 0
    for epoch in range(int(epochs)):
        for i, (images, labels) in enumerate(train_loader):
            images = Variable(images.view(-1, 28 * 28))
            labels = Variable(labels)

            optimizer.zero_grad()
            outputs = model(images)
            loss = criterion(outputs, labels)
            loss.backward()
            optimizer.step()

            iter+=1
            if iter%500==0:
                # 计算准确率
                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)
                    # 如果用的是 GPU，则要把预测值和标签都取回 CPU，才能用 Python 来计算
                    correct+= (predicted == labels).sum()
                accuracy = 100 * correct/total
                print("Iteration: {}. Loss: {}. Accuracy: {}.".format(iter, loss.item(), accuracy))

def ordinal_regression():
    X = np.array([
        [0.5, 0.1, -0.1],
        [1.0, 0.2, 0.6],
        [-2.0, 0.4, 0.8]
        ], dtype=np.float32)

    y = np.array([0, 1, 2]).reshape(-1, 1)

    num_features = X.shape[1]
    num_classes = len(np.unique(y))

    predictor = nn.Sequential(
        nn.Linear(num_features, num_features),
        nn.ReLU(),
        nn.Linear(num_features, 1)
    )

    model = OrdinalLogisticModel(predictor, num_classes)

    y_pred = model(torch.as_tensor(X))

    print(y_pred) 

    # tensor([[0.2325, 0.2191, 0.5485],
    #         [0.2324, 0.2191, 0.5485],
    #         [0.2607, 0.2287, 0.5106]], grad_fn=<CatBackward>)

    skorch_model = NeuralNet(
        module=OrdinalLogisticModel,
        module__predictor=predictor,
        module__num_classes=num_classes,
        criterion=CumulativeLinkLoss,
        train_split=None,
        max_epochs= 30,
        callbacks=[
            ('ascension', AscensionCallback())
        ],
    )

    skorch_model.fit(X, y)

    # train_acc = model.history[:, 'train_accuracy']
    # valid_acc = model.history[:, 'valid_accuracy']

    # plt.plot(train_acc, label='Train Accuracy')
    # plt.plot(valid_acc, label='Validation Accuracy')
    # plt.xlabel('Epoch')
    # plt.ylabel('Accuracy')
    # plt.legend()
    # plt.show()