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MNIST数据集 

MNIST手写数字数据集是机器学习领域中广泛使用的图像分类数据集。它包含60,000个训练样本和10,000个测试样本。这些数字已进行尺寸规格化，并在固定尺寸的图像中居中。每个样本都是一个784×1的矩阵，是从原始的28×28灰度图像转换而来的。MNIST中的数字范围是0到9。下面显示了一些示例。 注意：在训练期间，切勿以任何形式使用有关测试样本的信息。

代码清单

• data/ 文件夹：存放MNIST数据集。下载数据，解压后存放于该文件夹下。下载链接：MNIST handwritten digit database, Yann LeCun, Corinna Cortes and Chris Burges
• solver.py 这个文件中实现了训练和测试的流程。；
• dataloader.py 实现了数据加载器，可用于准备数据以进行训练和测试；
• visualize.py 实现了plot_loss_and_acc函数，该函数可用于绘制损失和准确率曲线；
• optimizer.py 实现带momentum的SGD优化器，可用于执行参数更新；
• loss.py 实现softmax_cross_entropy_loss，包含loss的计算和梯度计算；
• runner.ipynb 完成所有代码后的执行文件，执行训练和测试过程。

要求

1. 记录训练和测试的准确率。画出训练损失和准确率曲线；
2. 比较使用和不使用momentum结果的不同，可以从训练时间，收敛性和准确率等方面讨论差异；
3. 调整其他超参数，如学习率，Batchsize等，观察这些超参数如何影响分类性能。写下观察结果并将这些新结果记录在报告中。

运行结果如下：

代码如下：

solver.py

import numpy as np

from layers import FCLayer

from dataloader import build_dataloader
from network import Network
from optimizer import SGD
from loss import SoftmaxCrossEntropyLoss
from visualize import plot_loss_and_acc

class Solver(object):
    def __init__(self, cfg):
        self.cfg = cfg

        # build dataloader
        train_loader, val_loader, test_loader = self.build_loader(cfg)
        self.train_loader = train_loader
        self.val_loader = val_loader
        self.test_loader = test_loader

        # build model
        self.model = self.build_model(cfg)

        # build optimizer
        self.optimizer = self.build_optimizer(self.model, cfg)

        # build evaluation criterion
        self.criterion = SoftmaxCrossEntropyLoss()

    @staticmethod
    def build_loader(cfg):
        train_loader = build_dataloader(
            cfg['data_root'], cfg['max_epoch'], cfg['batch_size'], shuffle=True, mode='train')

        val_loader = build_dataloader(
            cfg['data_root'], 1, cfg['batch_size'], shuffle=False, mode='val')

        test_loader = build_dataloader(
            cfg['data_root'], 1, cfg['batch_size'], shuffle=False, mode='test')

        return train_loader, val_loader, test_loader

    @staticmethod
    def build_model(cfg):
        model = Network()
        model.add(FCLayer(784, 10))
        return model

    @staticmethod
    def build_optimizer(model, cfg):
        return SGD(model, cfg['learning_rate'], cfg['momentum'])

    def train(self):
        max_epoch = self.cfg['max_epoch']

        epoch_train_loss, epoch_train_acc = [], []
        for epoch in range(max_epoch):

            iteration_train_loss, iteration_train_acc = [], []
            for iteration, (images, labels) in enumerate(self.train_loader):
                # forward pass
                logits = self.model.forward(images)
                loss, acc = self.criterion.forward(logits, labels)

                # backward_pass
                delta = self.criterion.backward()
                self.model.backward(delta)

                # updata the model weights
                self.optimizer.step()

                # restore loss and accuracy
                iteration_train_loss.append(loss)
                iteration_train_acc.append(acc)

                # display iteration training info
                if iteration % self.cfg['display_freq'] == 0:
                    print("Epoch [{}][{}]\t Batch [{}][{}]\t Training Loss {:.4f}\t Accuracy {:.4f}".format(
                        epoch, max_epoch, iteration, len(self.train_loader), loss, acc))

            avg_train_loss, avg_train_acc = np.mean(iteration_train_loss), np.mean(iteration_train_acc)
            epoch_train_loss.append(avg_train_loss)
            epoch_train_acc.append(avg_train_acc)

            # validate
            avg_val_loss, avg_val_acc = self.validate()

            # display epoch training info
            print('\nEpoch [{}]\t Average training loss {:.4f}\t Average training accuracy {:.4f}'.format(
                epoch, avg_train_loss, avg_train_acc))

            # display epoch valiation info
            print('Epoch [{}]\t Average validation loss {:.4f}\t Average validation accuracy {:.4f}\n'.format(
                epoch, avg_val_loss, avg_val_acc))

        return epoch_train_loss, epoch_train_acc

    def validate(self):
        logits_set, labels_set = [], []
        for images, labels in self.val_loader:
            logits = self.model.forward(images)
            logits_set.append(logits)
            labels_set.append(labels)

        logits = np.concatenate(logits_set)
        labels = np.concatenate(labels_set)
        loss, acc = self.criterion.forward(logits, labels)
        return loss, acc

    def test(self):
        logits_set, labels_set = [], []
        for images, labels in self.test_loader:
            logits = self.model.forward(images)
            logits_set.append(logits)
            labels_set.append(labels)

        logits = np.concatenate(logits_set)
        labels = np.concatenate(labels_set)
        loss, acc = self.criterion.forward(logits, labels)
        return loss, acc


if __name__ == '__main__':
    # You can modify the hyerparameters by yourself.
    relu_cfg = {
        'data_root': 'data',
        'max_epoch': 10,
        'batch_size': 100,
        'learning_rate': 0.1,
        'momentum': 0.9,
        'display_freq': 50,
        'activation_function': 'relu',
    }

    runner = Solver(relu_cfg)
    relu_loss, relu_acc = runner.train()

    test_loss, test_acc = runner.test()
    print('Final test accuracy {:.4f}\n'.format(test_acc))

    # You can modify the hyerparameters by yourself.
    sigmoid_cfg = {
        'data_root': 'data',
        'max_epoch': 10,
        'batch_size': 100,
        'learning_rate': 0.1,
        'momentum': 0.9,
        'display_freq': 50,
        'activation_function': 'sigmoid',
    }

    runner = Solver(sigmoid_cfg)
    sigmoid_loss, sigmoid_acc = runner.train()

    test_loss, test_acc = runner.test()
    print('Final test accuracy {:.4f}\n'.format(test_acc))

    plot_loss_and_acc({
        "relu": [relu_loss, relu_acc],
        "sigmoid": [sigmoid_loss, sigmoid_acc],
    })

dataloader.py

import os
import struct
import numpy as np


class Dataset(object):

    def __init__(self, data_root, mode='train', num_classes=10):
        assert mode in ['train', 'val', 'test']

        # load images and labels
        kind = {'train': 'train', 'val': 'train', 'test': 't10k'}[mode]
        labels_path = os.path.join(data_root, '{}-labels-idx1-ubyte'.format(kind))
        images_path = os.path.join(data_root, '{}-images-idx3-ubyte'.format(kind))

        with open(labels_path, 'rb') as lbpath:
            magic, n = struct.unpack('>II', lbpath.read(8))
            labels = np.fromfile(lbpath, dtype=np.uint8)

        with open(images_path, 'rb') as imgpath:
            magic, num, rows, cols = struct.unpack('>IIII', imgpath.read(16))
            images = np.fromfile(imgpath, dtype=np.uint8).reshape(len(labels), 784)

        if mode == 'train':
            # training images and labels
            self.images = images[:55000]  # shape: (55000, 784)
            self.labels = labels[:55000]  # shape: (55000,)

        elif mode == 'val':
            # validation images and labels
            self.images = images[55000:]  # shape: (5000, 784)
            self.labels = labels[55000:]  # shape: (5000, )

        else:
            # test data
            self.images = images  # shape: (10000, 784)
            self.labels = labels  # shape: (10000, )

        self.num_classes = 10

    def __len__(self):
        return len(self.images)

    def __getitem__(self, idx):
        image = self.images[idx]
        label = self.labels[idx]

        # Normalize from [0, 255.] to [0., 1.0], and then subtract by the mean value
        image = image / 255.0
        image = image - np.mean(image)

        return image, label


class IterationBatchSampler(object):

    def __init__(self, dataset, max_epoch, batch_size=2, shuffle=True):
        self.dataset = dataset
        self.batch_size = batch_size
        self.shuffle = shuffle

    def prepare_epoch_indices(self):
        indices = np.arange(len(self.dataset))

        if self.shuffle:
            np.random.shuffle(indices)

        num_iteration = len(indices) // self.batch_size + int(len(indices) % self.batch_size)
        self.batch_indices = np.split(indices, num_iteration)

    def __iter__(self):
        return iter(self.batch_indices)

    def __len__(self):
        return len(self.batch_indices)


class Dataloader(object):

    def __init__(self, dataset, sampler):
        self.dataset = dataset
        self.sampler = sampler

    def __iter__(self):
        self.sampler.prepare_epoch_indices()

        for batch_indices in self.sampler:
            batch_images = []
            batch_labels = []
            for idx in batch_indices:
                img, label = self.dataset[idx]
                batch_images.append(img)
                batch_labels.append(label)

            batch_images = np.stack(batch_images)
            batch_labels = np.stack(batch_labels)

            yield batch_images, batch_labels

    def __len__(self):
        return len(self.sampler)


def build_dataloader(data_root, max_epoch, batch_size, shuffle=False, mode='train'):
    dataset = Dataset(data_root, mode)
    sampler = IterationBatchSampler(dataset, max_epoch, batch_size, shuffle)
    data_lodaer = Dataloader(dataset, sampler)
    return data_lodaer

loss.py

import numpy as np

# a small number to prevent dividing by zero, maybe useful for you
EPS = 1e-11

class SoftmaxCrossEntropyLoss(object):

    def forward(self, logits, labels):
        """
          Inputs: (minibatch)
          - logits: forward results from the last FCLayer, shape (batch_size, 10)
          - labels: the ground truth label, shape (batch_size, )
        """

        ############################################################################
        # TODO: Put your code here
        # Calculate the average accuracy and loss over the minibatch
        # Return the loss and acc, which will be used in solver.py
        # Hint: Maybe you need to save some arrays for backward

        self.one_hot_labels = np.zeros_like(logits)
        self.one_hot_labels[np.arange(len(logits)), labels] = 1

        self.prob = np.exp(logits) / (EPS + np.exp(logits).sum(axis=1, keepdims=True))

        # calculate the accuracy
        preds = np.argmax(self.prob, axis=1) # self.prob, not logits.
        acc = np.mean(preds == labels)

        # calculate the loss
        loss = np.sum(-self.one_hot_labels * np.log(self.prob + EPS), axis=1)
        loss = np.mean(loss)
        ############################################################################

        return loss, acc

    def backward(self):

        ############################################################################
        # TODO: Put your code here
        # Calculate and return the gradient (have the same shape as logits)

        return self.prob - self.one_hot_labels
        ############################################################################

network.py

class Network(object):
    def __init__(self):
        self.layerList = []
        self.numLayer = 0

    def add(self, layer):
        self.numLayer += 1
        self.layerList.append(layer)

    def forward(self, x):
        # forward layer by layer
        for i in range(self.numLayer):
            x = self.layerList[i].forward(x)
        return x

    def backward(self, delta):
        # backward layer by layer
        for i in reversed(range(self.numLayer)): # reversed
            delta = self.layerList[i].backward(delta)

optimizer.py

import numpy as np

class SGD(object):
    def __init__(self, model, learning_rate, momentum=0.0):
        self.model = model
        self.learning_rate = learning_rate
        self.momentum = momentum

    def step(self):
        """One backpropagation step, update weights layer by layer"""

        layers = self.model.layerList
        for layer in layers:
            if layer.trainable:

                ############################################################################
                # TODO: Put your code here
                # Calculate diff_W and diff_b using layer.grad_W and layer.grad_b.
                # You need to add momentum to this.

                # Weight update with momentum
                if not hasattr(layer, 'diff_W'):
                    layer.diff_W = 0.0

                layer.diff_W = layer.grad_W + self.momentum * layer.diff_W
                layer.diff_b = layer.grad_b

                layer.W += -self.learning_rate * layer.diff_W
                layer.b += -self.learning_rate * layer.diff_b

                # # Weight update without momentum
                # layer.W += -self.learning_rate * layer.grad_W
                # layer.b += -self.learning_rate * layer.grad_b

                ############################################################################

visualize.py

import matplotlib.pyplot as plt
import numpy as np

def plot_loss_and_acc(loss_and_acc_dict):
    # visualize loss curve
    plt.figure()

    min_loss, max_loss = 100.0, 0.0
    for key, (loss_list, acc_list) in loss_and_acc_dict.items():
        min_loss = min(loss_list) if min(loss_list) < min_loss else min_loss
        max_loss = max(loss_list) if max(loss_list) > max_loss else max_loss

        num_epoch = len(loss_list)
        plt.plot(range(1, 1 + num_epoch), loss_list, '-s', label=key)

    plt.xlabel('Epoch')
    plt.ylabel('Loss')
    plt.legend()
    plt.xticks(range(0, num_epoch + 1, 2))
    plt.axis([0, num_epoch + 1, min_loss - 0.1, max_loss + 0.1])
    plt.show()

    # visualize acc curve
    plt.figure()

    min_acc, max_acc = 1.0, 0.0
    for key, (loss_list, acc_list) in loss_and_acc_dict.items():
        min_acc = min(acc_list) if min(acc_list) < min_acc else min_acc
        max_acc = max(acc_list) if max(acc_list) > max_acc else max_acc

        num_epoch = len(acc_list)
        plt.plot(range(1, 1 + num_epoch), acc_list, '-s', label=key)

    plt.xlabel('Epoch')
    plt.ylabel('Accuracy')
    plt.legend()
    plt.xticks(range(0, num_epoch + 1, 2))
    plt.axis([0, num_epoch + 1, min_acc, 1.0])
    plt.show()