{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "3b57686b-7ac8-4897-bf76-3d982b1ff8da",
   "metadata": {},
   "source": [
    "![school-logo](https://github.com/typingbugs/School-DeepLearningCourse-Lab/blob/main/images/school_logo.png)\n",
    "\n",
    "<h1><center>本科生《深度学习》课程<br>实验报告</center></h1>\n",
    "<div style=\"text-align: center;\">\n",
    "    <div><span style=\"display: inline-block; width: 65px; text-align: center;\">课程名称</span><span style=\"display: inline-block; width: 25px;\">:</span><span style=\"display: inline-block; width: 210px; font-weight: bold; text-align: left;\">深度学习</span></div>\n",
    "    <div><span style=\"display: inline-block; width: 65px; text-align: center;\">实验题目</span><span style=\"display: inline-block; width: 25px;\">:</span><span style=\"display: inline-block; width: 210px; font-weight: bold; text-align: left;\">Pytorch基本操作</span></div>\n",
    "    <div><span style=\"display: inline-block; width: 65px; text-align: center;\">学号</span><span style=\"display: inline-block; width: 25px;\">:</span><span style=\"display: inline-block; width: 210px; font-weight: bold; text-align: left;\">21281280</span></div>\n",
    "    <div><span style=\"display: inline-block; width: 65px; text-align: center;\">姓名</span><span style=\"display: inline-block; width: 25px;\">:</span><span style=\"display: inline-block; width: 210px; font-weight: bold; text-align: left;\">柯劲帆</span></div>\n",
    "    <div><span style=\"display: inline-block; width: 65px; text-align: center;\">班级</span><span style=\"display: inline-block; width: 25px;\">:</span><span style=\"display: inline-block; width: 210px; font-weight: bold; text-align: left;\">物联网2101班</span></div>\n",
    "    <div><span style=\"display: inline-block; width: 65px; text-align: center;\">指导老师</span><span style=\"display: inline-block; width: 25px;\">:</span><span style=\"display: inline-block; width: 210px; font-weight: bold; text-align: left;\">张淳杰</span></div>\n",
    "    <div><span style=\"display: inline-block; width: 65px; text-align: center;\">报告日期</span><span style=\"display: inline-block; width: 25px;\">:</span><span style=\"display: inline-block; width: 210px; font-weight: bold; text-align: left;\">2023年10月9日</span></div>\n",
    "</div>"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "e24aa17e-faf9-4d69-9eae-43159116b56f",
   "metadata": {},
   "source": [
    "实验环境:\n",
    "- OS:Ubuntu 22.04 内核版本 6.2.0-34-generic\n",
    "- CPU:12th Gen Intel(R) Core(TM) i7-12700H\n",
    "- GPU:NVIDIA GeForce RTX 3070 Ti Laptop\n",
    "- conda: miniconda 23.9.0\n",
    "- python:3.10.13\n",
    "- pytorch:2.1.0"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "a4e12268-bad4-44c4-92d5-883624d93e25",
   "metadata": {},
   "outputs": [],
   "source": [
    "import numpy as np\n",
    "import torch\n",
    "from torch.autograd import Variable\n",
    "from torch.utils.data import Dataset, DataLoader\n",
    "from torch import nn\n",
    "from torchvision import datasets, transforms"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "cc7f0ce5-d613-425b-807c-78115632cd80",
   "metadata": {},
   "source": [
    "引用相关库。"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "59a43d35-56ac-4ade-995d-1c6fcbcd1262",
   "metadata": {},
   "source": [
    "# 一、Pytorch基本操作考察\n",
    "## 题目2\n",
    "**使用 𝐓𝐞𝐧𝐬𝐨𝐫 初始化一个 𝟏×𝟑 的矩阵 𝑴 和一个 𝟐×𝟏 的矩阵 𝑵,对两矩阵进行减法操作(要求实现三种不同的形式),给出结果并分析三种方式的不同(如果出现报错,分析报错的原因),同时需要指出在计算过程中发生了什么。**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "79ea46db-cf49-436c-9b5b-c6562d0da9e2",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "方法1的结果:\n",
      "tensor([[-3, -2, -1],\n",
      "        [-4, -3, -2]])\n",
      "方法2的结果:\n",
      "tensor([[-3, -2, -1],\n",
      "        [-4, -3, -2]])\n",
      "方法3的结果:\n",
      "tensor([[-3, -2, -1],\n",
      "        [-4, -3, -2]])\n"
     ]
    }
   ],
   "source": [
    "A = torch.tensor([[1, 2, 3]])\n",
    "\n",
    "B = torch.tensor([[4],\n",
    "                  [5]])\n",
    "\n",
    "# 方法1: 使用PyTorch的减法操作符\n",
    "result1 = A - B\n",
    "\n",
    "# 方法2: 使用PyTorch的sub函数\n",
    "result2 = torch.sub(A, B)\n",
    "\n",
    "# 方法3: 手动实现广播机制并作差\n",
    "def mysub(a:torch.Tensor, b:torch.Tensor):\n",
    "    if not (\n",
    "        (a.size(0) == 1 and b.size(1) == 1) \n",
    "        or \n",
    "        (a.size(1) == 1 and b.size(0) == 1)\n",
    "        ):\n",
    "        raise ValueError(\"输入的张量大小无法满足广播机制的条件。\")\n",
    "    else:\n",
    "        target_shape = torch.Size([max(A.size(0), B.size(0)), max(A.size(1), B.size(1))])\n",
    "        A_broadcasted = A.expand(target_shape)\n",
    "        B_broadcasted = B.expand(target_shape)\n",
    "        result = torch.zeros(target_shape, dtype=torch.int64).to(device=A_broadcasted.device)\n",
    "        for i in range(target_shape[0]):\n",
    "            for j in range(target_shape[1]):\n",
    "                result[i, j] = A_broadcasted[i, j] - B_broadcasted[i, j]\n",
    "        return result\n",
    "\n",
    "result3 = mysub(A, B)\n",
    "\n",
    "print(\"方法1的结果:\")\n",
    "print(result1)\n",
    "print(\"方法2的结果:\")\n",
    "print(result2)\n",
    "print(\"方法3的结果:\")\n",
    "print(result3)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "2489a3ad-f6ff-4561-bb26-e02654090b98",
   "metadata": {},
   "source": [
    "## 题目2\n",
    "1. **利用Tensor创建两个大小分别3*2和4*2的随机数矩阵P和Q,要求服从均值为0,标准差0.01为的正态分布;**\n",
    "2. **对第二步得到的矩阵Q进行形状变换得到Q的转置Q^T;**\n",
    "3. **对上述得到的矩阵P和矩阵Q^T求矩阵相乘。**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "41e4ee02-1d05-4101-b3f0-477bac0277fb",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "矩阵 P:\n",
      "tensor([[ 0.0053,  0.0013],\n",
      "        [-0.0086,  0.0136],\n",
      "        [-0.0013,  0.0176]])\n",
      "矩阵 Q:\n",
      "tensor([[ 0.0044,  0.0014],\n",
      "        [ 0.0147,  0.0078],\n",
      "        [-0.0002, -0.0023],\n",
      "        [ 0.0001, -0.0011]])\n",
      "矩阵 QT:\n",
      "tensor([[ 0.0044,  0.0147, -0.0002,  0.0001],\n",
      "        [ 0.0014,  0.0078, -0.0023, -0.0011]])\n",
      "矩阵相乘的结果:\n",
      "tensor([[ 2.4953e-05,  8.7463e-05, -3.8665e-06, -8.9576e-07],\n",
      "        [-1.9514e-05, -2.0557e-05, -2.9649e-05, -1.5913e-05],\n",
      "        [ 1.8189e-05,  1.1834e-04, -4.0097e-05, -1.9608e-05]])\n"
     ]
    }
   ],
   "source": [
    "mean = 0\n",
    "stddev = 0.01\n",
    "\n",
    "P = torch.normal(mean=mean, std=stddev, size=(3, 2))\n",
    "Q = torch.normal(mean=mean, std=stddev, size=(4, 2))\n",
    "\n",
    "print(\"矩阵 P:\")\n",
    "print(P)\n",
    "print(\"矩阵 Q:\")\n",
    "print(Q)\n",
    "\n",
    "# 对矩阵Q进行转置操作,得到矩阵Q的转置Q^T\n",
    "QT = Q.T\n",
    "print(\"矩阵 QT:\")\n",
    "print(QT)\n",
    "\n",
    "# 计算矩阵P和矩阵Q^T的矩阵相乘\n",
    "result = torch.matmul(P, QT)\n",
    "print(\"矩阵相乘的结果:\")\n",
    "print(result)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "cea9cb6d-adde-4e08-b9f2-8c417abf4231",
   "metadata": {},
   "source": [
    "## 题目2\n",
    "**给定公式$ y_3=y_1+y_2=𝑥^2+𝑥^3$,且$x=1$。利用学习所得到的Tensor的相关知识,求$y_3$对$x$的梯度,即$\\frac{dy_3}{dx}$。**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "951512cd-d915-4d04-959f-eb99d1971e2d",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "梯度(dy_3/dx):  2.0\n"
     ]
    }
   ],
   "source": [
    "x = torch.tensor(1.0, requires_grad=True)\n",
    "y_1 = x ** 2\n",
    "with torch.no_grad():\n",
    "    y_2 = x**3\n",
    "\n",
    "y3 = y_1 + y_2\n",
    "\n",
    "y3.backward()\n",
    "\n",
    "print(\"梯度(dy_3/dx): \", x.grad.item())"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "3269dbf6-889a-49eb-8094-1e588e1a6c30",
   "metadata": {},
   "source": [
    "# 二、动手实现logistic回归\n",
    "## 题目1\n",
    "**要求动手从0实现 logistic 回归(只借助Tensor和Numpy相关的库)在人工构造的数据集上进行训练和测试,并从loss以及训练集上的准确率等多个角度对结果进行分析(可借助nn.BCELoss或nn.BCEWithLogitsLoss作为损失函数,从零实现二元交叉熵为选作)**"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "bcd12aa9-f187-4d88-8c59-af6d16107edb",
   "metadata": {},
   "source": [
    "给定预测概率$ \\left( \\hat{y} \\right) $和目标标签$ \\left( y \\right)$(通常是0或1),BCELoss的计算公式如下:\n",
    "$$\n",
    " \\text{BCELoss}(\\hat{y}, y) = -\\frac{1}{N} \\sum_{i=1}^{N} \\left(y_i \\cdot \\log(\\hat{y}_i) + (1 - y_i) \\cdot \\log(1 - \\hat{y}_i)\\right) \n",
    "$$\n",
    "其中,$\\left( N \\right) $是样本数量,$\\left( \\hat{y}_i \\right) $表示模型的预测概率向量中的第$ \\left( i \\right) $个元素,$\\left( y_i \\right) $表示实际的目标标签中的第$ \\left( i \\right) $个元素。在二分类问题中,$\\left( y_i \\right) $通常是0或1。这个公式表示对所有样本的二分类交叉熵损失进行了求和并取平均。\n",
    "\n",
    "因此BCELoss的手动实现如下。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "e31b86ec-4114-48dd-8d73-fe4e0686419a",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "输入:\n",
      "tensor([0.6900])\n",
      "标签:\n",
      "tensor([1.])\n",
      "My_BCELoss损失值: 0.37110066413879395\n",
      "nn.BCELoss损失值: 0.37110066413879395\n"
     ]
    }
   ],
   "source": [
    "class My_BCELoss:\n",
    "    def __call__(self, prediction: torch.Tensor, target: torch.Tensor):\n",
    "        loss = -torch.mean(target * torch.log(prediction) + (1 - target) * torch.log(1 - prediction))\n",
    "        return loss\n",
    "\n",
    "\n",
    "# 测试\n",
    "prediction = torch.sigmoid(torch.tensor([0.8]))\n",
    "target = torch.tensor([1.0])\n",
    "print(f\"输入:\\n{prediction}\")\n",
    "print(f\"标签:\\n{target}\")\n",
    "\n",
    "my_bce_loss = My_BCELoss()\n",
    "my_loss = my_bce_loss(prediction, target)\n",
    "print(\"My_BCELoss损失值:\", my_loss.item())\n",
    "\n",
    "nn_bce_loss = nn.BCELoss()\n",
    "nn_loss = nn_bce_loss(prediction, target)\n",
    "print(\"nn.BCELoss损失值:\", nn_loss.item())"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "345b0300-8808-4c43-9bf9-05a7e6e1f5af",
   "metadata": {},
   "source": [
    "Optimizer的实现较为简单。\n",
    "\n",
    "主要实现:\n",
    "- 传入参数:`__init__()`\n",
    "- 对传入的参数进行更新:`step()`\n",
    "- 清空传入参数存储的梯度:`zero_grad()`"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "0297066c-9fc1-448d-bdcb-29a6f1519117",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "y.backward()之后,x的梯度:  2.0\n",
      "optimizer_test.step()之后,x的值:  0.800000011920929\n",
      "optimizer_test.zero_grad()之后,x的梯度:  0.0\n"
     ]
    }
   ],
   "source": [
    "class My_optimizer:\n",
    "    def __init__(self, params: list[torch.Tensor], lr: float):\n",
    "        self.params = params\n",
    "        self.lr = lr\n",
    "\n",
    "    def step(self):\n",
    "        for param in self.params:\n",
    "            param.data = param.data - self.lr * param.grad.data\n",
    "\n",
    "    def zero_grad(self):\n",
    "        for param in self.params:\n",
    "            if param.grad is not None:\n",
    "                param.grad.data.zero_()\n",
    "\n",
    "\n",
    "# 测试\n",
    "x = torch.tensor(1.0, requires_grad=True)\n",
    "y = x ** 2\n",
    "optimizer_test = My_optimizer([x], lr=0.1)\n",
    "\n",
    "y.backward()\n",
    "print(\"y.backward()之后,x的梯度: \", x.grad.item())\n",
    "\n",
    "optimizer_test.step()\n",
    "print(\"optimizer_test.step()之后,x的值: \", x.item())\n",
    "\n",
    "optimizer_test.zero_grad()\n",
    "print(\"optimizer_test.zero_grad()之后,x的梯度: \", x.grad.item())"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "6ab83528-a88b-4d66-b0c9-b1315cf75c22",
   "metadata": {},
   "source": [
    "线性层主要有一个权重(weight)和一个偏置(bias)。\n",
    "线性层的数学公式如下:\n",
    "$$\n",
    "x:=x \\times weight^T+bias\n",
    "$$\n",
    "因此代码实现如下:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "8e18695a-d8c5-4f77-8b5c-de40d9240fb9",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "输入:\n",
      "tensor([[1.],\n",
      "        [2.]], requires_grad=True)\n",
      "权重:\n",
      "tensor([[-1.0980],\n",
      "        [-0.5413],\n",
      "        [ 1.5884]], requires_grad=True)\n",
      "偏置:\n",
      "tensor([-1.1733], requires_grad=True)\n",
      "输出:\n",
      "tensor([[-2.2713, -1.7146,  0.4151],\n",
      "        [-3.3692, -2.2559,  2.0036]], grad_fn=<AddBackward0>)\n"
     ]
    }
   ],
   "source": [
    "class My_Linear:\n",
    "    def __init__(self, input_feature: int, output_feature: int):\n",
    "        self.weight = torch.randn((output_feature, input_feature), requires_grad=True, dtype=torch.float32)\n",
    "        self.bias = torch.randn(1, requires_grad=True, dtype=torch.float32)\n",
    "        self.params = [self.weight, self.bias]\n",
    "\n",
    "    def __call__(self, x: torch.Tensor):\n",
    "        return self.forward(x)\n",
    "\n",
    "    def forward(self, x: torch.Tensor):\n",
    "        x = torch.matmul(x, self.weight.T) + self.bias\n",
    "        return x\n",
    "\n",
    "    def to(self, device: str):\n",
    "        for param in self.params:\n",
    "            param.data = param.data.to(device=device)\n",
    "        return self\n",
    "\n",
    "    def parameters(self):\n",
    "        return self.params\n",
    "\n",
    "        \n",
    "# 测试\n",
    "linear_test = My_Linear(1, 3)\n",
    "x = torch.tensor([[1.], [2.]], requires_grad=True)\n",
    "print(f\"输入:\\n{x}\")\n",
    "print(f\"权重:\\n{linear_test.weight}\")\n",
    "print(f\"偏置:\\n{linear_test.bias}\")\n",
    "y = linear_test(x)\n",
    "print(f\"输出:\\n{y}\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "5ff813cc-c1f0-4c73-a3e8-d6796ef5d366",
   "metadata": {},
   "source": [
    "手动实现logistic回归模型。\n",
    "\n",
    "模型很简单,主要由一个线性层和一个sigmoid层组成。\n",
    "\n",
    "Sigmoid函数(又称为 Logistic函数)是一种常用的激活函数,通常用于神经网络的输出层或隐藏层,其作用是将输入的实数值压缩到一个范围在0和1之间的数值。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "e7de7e4b-a084-4793-812e-46e8550ecd8d",
   "metadata": {},
   "outputs": [],
   "source": [
    "class Model_2_1():\n",
    "    def __init__(self):\n",
    "        self.linear = My_Linear(1, 1)\n",
    "        self.params = self.linear.params\n",
    "\n",
    "    def __call__(self, x):\n",
    "        return self.forward(x)\n",
    "\n",
    "    def forward(self, x):\n",
    "        x = self.linear(x)\n",
    "        x = torch.sigmoid(x)\n",
    "        return x\n",
    "\n",
    "    def to(self, device: str):\n",
    "        for param in self.params:\n",
    "            param.data = param.data.to(device=device)\n",
    "        return self\n",
    "\n",
    "    def parameters(self):\n",
    "        return self.params"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "e14acea9-e5ef-4c24-aea9-329647224ce1",
   "metadata": {},
   "source": [
    "人工随机构造数据集。\n",
    "\n",
    "这里我遇到了比较大的问题。因为数据构建不合适,会导致后面的训练出现梯度爆炸。\n",
    "\n",
    "我采用随机产生数据后归一化的方法,即\n",
    "$$\n",
    "\\hat{x} = \\frac{x - \\text{min}_x}{\\text{max}_x - \\text{min}_x} \n",
    "$$\n",
    "将数据控制在合适的区间。\n",
    "\n",
    "我的y设置为$4-3\\times x + noise$,noise为随机噪声。\n",
    "\n",
    "生成完x和y后进行归一化处理,并写好DataLoader访问数据集的接口`__getitem__()`。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "c39fbafb-62e4-4b8c-9d65-6718d25f2970",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "测试数据集大小:100\n",
      "测试数据集第0对数据:\n",
      "x_0 = 0.5531462811708403\n",
      "y_0 = 0.42036701080526284\n"
     ]
    }
   ],
   "source": [
    "class My_Dataset(Dataset):\n",
    "    def __init__(self, data_size=1000000):\n",
    "        np.random.seed(0)\n",
    "        x = 2 * np.random.rand(data_size, 1)\n",
    "        noise = 0.2 * np.random.randn(data_size, 1)\n",
    "        y = 4 - 3 * x + noise\n",
    "        self.min_x, self.max_x = np.min(x), np.max(x)\n",
    "        min_y, max_y = np.min(y), np.max(y)\n",
    "        x = (x - self.min_x) / (self.max_x - self.min_x)\n",
    "        y = (y - min_y) / (max_y - min_y)\n",
    "        self.data = [[x[i][0], y[i][0]] for i in range(x.shape[0])]\n",
    "\n",
    "    def __len__(self):\n",
    "        return len(self.data)\n",
    "\n",
    "    def __getitem__(self, index):\n",
    "        x, y = self.data[index]\n",
    "        return x, y\n",
    "\n",
    "\n",
    "# 测试\n",
    "dataset_test = My_Dataset(data_size=100)\n",
    "dataset_size = len(dataset_test)\n",
    "print(f\"测试数据集大小:{dataset_size}\")\n",
    "x0, y0 = dataset_test[0]\n",
    "print(f\"测试数据集第0对数据:\")\n",
    "print(f\"x_0 = {x0}\")\n",
    "print(f\"y_0 = {y0}\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "957a76a2-b306-47a8-912e-8fbf00cdfd42",
   "metadata": {},
   "source": [
    "训练Logistic回归模型。\n",
    "进行如下步骤:\n",
    "1. 初始化超参数\n",
    "2. 获取数据集\n",
    "3. 初始化模型\n",
    "4. 定义损失函数和优化器\n",
    "5. 训练\n",
    "    1. 从训练dataloader中获取批量数据\n",
    "    2. 传入模型\n",
    "    3. 使用损失函数计算与ground_truth的损失\n",
    "    4. 使用优化器进行反向传播\n",
    "    5. 循环以上步骤\n",
    "6. 测试\n",
    "    1. 设置测试数据\n",
    "    2. 传入模型\n",
    "    3. 得到预测值"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "id": "5612661e-2809-4d46-96c2-33ee9f44116d",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Epoch 1/10, Loss: 680.9198314547539, Acc: 0.9677169744703272\n",
      "Epoch 2/10, Loss: 677.2582936882973, Acc: 0.9985965700887113\n",
      "Epoch 3/10, Loss: 677.1911396384239, Acc: 0.9993738265049104\n",
      "Epoch 4/10, Loss: 677.1777537465096, Acc: 0.9995470920810262\n",
      "Epoch 5/10, Loss: 677.1745615005493, Acc: 0.9998228389835642\n",
      "Epoch 6/10, Loss: 677.1743944883347, Acc: 0.9999690339979311\n",
      "Epoch 7/10, Loss: 677.1735371947289, Acc: 0.9998205132243208\n",
      "Epoch 8/10, Loss: 677.1737813353539, Acc: 0.999798559017381\n",
      "Epoch 9/10, Loss: 677.1740361452103, Acc: 0.9998672931901137\n",
      "Epoch 10/10, Loss: 677.1736125349998, Acc: 0.9997257713704987\n",
      "Model weights: -0.0006128809181973338, bias: 0.023128816857933998\n",
      "Prediction for test data: 0.505628764629364\n"
     ]
    }
   ],
   "source": [
    "learning_rate = 5e-2\n",
    "num_epochs = 10\n",
    "batch_size = 1024\n",
    "device = \"cuda:0\" if torch.cuda.is_available() else \"cpu\"\n",
    "\n",
    "dataset = My_Dataset()\n",
    "dataloader = DataLoader(\n",
    "    dataset=dataset, batch_size=batch_size, shuffle=True, num_workers=5, pin_memory=True\n",
    ")\n",
    "\n",
    "model = Model_2_1().to(device)\n",
    "criterion = My_BCELoss()\n",
    "optimizer = My_optimizer(model.parameters(), lr=learning_rate)\n",
    "\n",
    "for epoch in range(num_epochs):\n",
    "    total_epoch_loss = 0\n",
    "    total_epoch_pred = 0\n",
    "    total_epoch_target = 0\n",
    "    for x, targets in dataloader:\n",
    "        optimizer.zero_grad()\n",
    "        \n",
    "        x = x.to(device).to(dtype=torch.float32)\n",
    "        targets = targets.to(device).to(dtype=torch.float32)\n",
    "        \n",
    "        x = x.unsqueeze(1)\n",
    "        y_pred = model(x)\n",
    "        loss = criterion(y_pred, targets)\n",
    "        total_epoch_loss += loss.item()\n",
    "        total_epoch_target += targets.sum().item()\n",
    "        total_epoch_pred += y_pred.sum().item()\n",
    "\n",
    "        loss.backward()\n",
    "        optimizer.step()\n",
    "\n",
    "    print(\n",
    "        f\"Epoch {epoch + 1}/{num_epochs}, Loss: {total_epoch_loss}, Acc: {1 - abs(total_epoch_pred - total_epoch_target) / total_epoch_target}\"\n",
    "    )\n",
    "\n",
    "with torch.no_grad():\n",
    "    test_data = (np.array([[2]]) - dataset.min_x) / (dataset.max_x - dataset.min_x)\n",
    "    test_data = Variable(\n",
    "        torch.tensor(test_data, dtype=torch.float32), requires_grad=False\n",
    "    ).to(device)\n",
    "    predicted = model(test_data).to(\"cpu\")\n",
    "    print(\n",
    "        f\"Model weights: {model.linear.weight.item()}, bias: {model.linear.bias.item()}\"\n",
    "    )\n",
    "    print(f\"Prediction for test data: {predicted.item()}\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9e416582-a30d-4084-acc6-6e05f80a6aff",
   "metadata": {},
   "source": [
    "## 题目2\n",
    "**利用 torch.nn 实现 logistic 回归在人工构造的数据集上进行训练和测试,并对结果进行分析,并从loss以及训练集上的准确率等多个角度对结果进行分析**"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "0460d125-7d03-44fe-845c-c4d13792e241",
   "metadata": {},
   "source": [
    "使用torch.nn实现模型。\n",
    "\n",
    "将之前的Model_2_1中的手动实现函数改为torch.nn内置函数即可,再加上继承nn.Module以使用torch.nn内置模型模板特性。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "id": "fa121afd-a1af-4193-9b54-68041e0ed068",
   "metadata": {},
   "outputs": [],
   "source": [
    "class Model_2_2(nn.Module):\n",
    "    def __init__(self):\n",
    "        super(Model_2_2, self).__init__()\n",
    "        self.linear = nn.Linear(1, 1, dtype=torch.float64)\n",
    "\n",
    "    def forward(self, x):\n",
    "        x = self.linear(x)\n",
    "        x = torch.sigmoid(x)\n",
    "        return x"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "176eee7e-4e3d-470e-8af2-8761bca039f8",
   "metadata": {},
   "source": [
    "训练与测试过程与之前手动实现的几乎一致。仅有少量涉及数据类型(dtype)的代码需要更改以适应torch.nn的内置函数要求。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "id": "93b0fdb6-be8b-4663-b59e-05ed19a9ea09",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Epoch 1/10, Loss: 600.8090852049173, Acc: 0.9945839732715815\n",
      "Epoch 2/10, Loss: 565.9542879898308, Acc: 0.9999073566261442\n",
      "Epoch 3/10, Loss: 565.9275637627202, Acc: 0.9999969933728429\n",
      "Epoch 4/10, Loss: 565.927609191542, Acc: 0.9999961959888584\n",
      "Epoch 5/10, Loss: 565.928202885308, Acc: 0.9999953721249991\n",
      "Epoch 6/10, Loss: 565.9323843971484, Acc: 0.9999969051674709\n",
      "Epoch 7/10, Loss: 565.9298919086365, Acc: 0.9999935973983517\n",
      "Epoch 8/10, Loss: 565.9299267993255, Acc: 0.9999985970973472\n",
      "Epoch 9/10, Loss: 565.9306044380719, Acc: 0.9999947955797296\n",
      "Epoch 10/10, Loss: 565.9329843268798, Acc: 0.9999973784035556\n",
      "Model weights: -3.7066140776793373, bias: 1.8709382558479912\n",
      "Prediction for test data: 0.13756338580653613\n"
     ]
    }
   ],
   "source": [
    "learning_rate = 1e-2\n",
    "num_epochs = 10\n",
    "batch_size = 1024\n",
    "device = \"cuda:0\" if torch.cuda.is_available() else \"cpu\"\n",
    "\n",
    "dataset = My_Dataset()\n",
    "dataloader = DataLoader(\n",
    "    dataset=dataset, batch_size=batch_size, shuffle=True, num_workers=5, pin_memory=True\n",
    ")\n",
    "\n",
    "model = Model_2_2().to(device)\n",
    "criterion = nn.BCELoss()\n",
    "optimizer = torch.optim.Adam(model.parameters(), lr=learning_rate)\n",
    "\n",
    "for epoch in range(num_epochs):\n",
    "    total_epoch_loss = 0\n",
    "    total_epoch_pred = 0\n",
    "    total_epoch_target = 0\n",
    "    for x, targets in dataloader:\n",
    "        optimizer.zero_grad()\n",
    "\n",
    "        x = x.to(device)\n",
    "        targets = targets.to(device)\n",
    "\n",
    "        x = x.unsqueeze(1)\n",
    "        targets = targets.unsqueeze(1)\n",
    "        y_pred = model(x)\n",
    "        loss = criterion(y_pred, targets)\n",
    "        total_epoch_loss += loss.item()\n",
    "        total_epoch_target += targets.sum().item()\n",
    "        total_epoch_pred += y_pred.sum().item()\n",
    "\n",
    "        loss.backward()\n",
    "        optimizer.step()\n",
    "\n",
    "    print(\n",
    "        f\"Epoch {epoch + 1}/{num_epochs}, Loss: {total_epoch_loss}, Acc: {1 - abs(total_epoch_pred - total_epoch_target) / total_epoch_target}\"\n",
    "    )\n",
    "\n",
    "with torch.no_grad():\n",
    "    test_data = (np.array([[2]]) - dataset.min_x) / (dataset.max_x - dataset.min_x)\n",
    "    test_data = Variable(\n",
    "        torch.tensor(test_data, dtype=torch.float64), requires_grad=False\n",
    "    ).to(device)\n",
    "    predicted = model(test_data).to(\"cpu\")\n",
    "    print(\n",
    "        f\"Model weights: {model.linear.weight.item()}, bias: {model.linear.bias.item()}\"\n",
    "    )\n",
    "    print(f\"Prediction for test data: {predicted.item()}\")\n"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "e6bff679-f8d2-46cc-bdcb-82af7dab38b3",
   "metadata": {},
   "source": [
    "对比发现,使用torch.nn的内置损失函数和优化器,正确率提升更快。\n",
    "\n",
    "但是为什么相同分布的数据集训练出的权重和偏置,以及预测结果存在较大差别,这个问题的原因还有待我探究。"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "ef41d7fa-c2bf-4024-833b-60af0a87043a",
   "metadata": {},
   "source": [
    "# 三、动手实现softmax回归\n",
    "\n",
    "## 问题1\n",
    "\n",
    "**要求动手从0实现softmax回归(只借助Tensor和Numpy相关的库)在Fashion-MNIST数据集上进行训练和测试,并从loss、训练集以及测试集上的准确率等多个角度对结果进行分析(要求从零实现交叉熵损失函数)**"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "3c356760-75a8-4814-ba69-73b270396a4e",
   "metadata": {},
   "source": [
    "手动实现nn.one_hot()。\n",
    "\n",
    "one-hot向量用于消除线性标签值所映射的类别的非线性。\n",
    "\n",
    "one-hot向量是使用一个长度为分类数量的数组表示标签值,其中有且仅有1个值为为1,该值的下标为标签值;其余为0。\n",
    "\n",
    "原理很简单,步骤如下:\n",
    "1. 初始化全零的张量,大小为(标签数量,分类数量);\n",
    "2. 将标签值映射到全零张量的\\[下标,标签值\\]中,将该位置为1;\n",
    "3. 返回修改后的张量,即是ont-hot向量。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "id": "e605f1b0-1d32-410f-bddf-402a85ccc9ff",
   "metadata": {},
   "outputs": [],
   "source": [
    "def my_one_hot(indices: torch.Tensor, num_classes: int):\n",
    "    one_hot_tensor = torch.zeros(len(indices), num_classes).to(indices.device)\n",
    "    one_hot_tensor.scatter_(1, indices.view(-1, 1), 1)\n",
    "    return one_hot_tensor"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "902603a6-bfb9-4ce3-bd0d-b00cebb1d3cb",
   "metadata": {},
   "source": [
    "手动实现CrossEntropyLoss。\n",
    "\n",
    "CrossEntropyLoss由一个log_softmax和一个nll_loss组成。\n",
    "\n",
    "softmax的数学表达式如下:\n",
    "$$\n",
    "\\text{softmax}(y_i) = \\frac{e^{y_i - \\text{max}(y)}}{\\sum_{j=1}^{N} e^{y_j - \\text{max}(y)}} \n",
    "$$\n",
    "log_softmax即为$\\log\\left(softmax\\left(y\\right)\\right)$。\n",
    "\n",
    "CrossEntropyLoss的数学表达式如下:\n",
    "$$\n",
    "\\text{CrossEntropyLoss}(y, \\hat{y}) = -\\frac{1}{N} \\sum_{i=1}^{N} \\hat{y}_i \\cdot \\log(\\text{softmax}(y_i)) \n",
    "$$\n",
    "\n",
    "故代码如下:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "id": "759a3bb2-b5f4-4ea5-a2d7-15f0c4cdd14b",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "输入:\n",
      "tensor([[-1.2914,  0.4715, -0.0432,  1.7427, -1.9236],\n",
      "        [ 0.5361, -0.7551, -0.6810,  1.0945,  0.6135],\n",
      "        [-1.3398, -0.0026, -1.6066, -0.4659, -1.6076]], requires_grad=True)\n",
      "标签:\n",
      "tensor([[1., 0., 0., 0., 0.],\n",
      "        [0., 0., 0., 0., 1.],\n",
      "        [0., 0., 0., 0., 1.]])\n",
      "My_CrossEntropyLoss损失值: 2.4310648441314697\n",
      "nn.CrossEntropyLoss损失值: 2.4310646057128906\n"
     ]
    }
   ],
   "source": [
    "class My_CrossEntropyLoss:\n",
    "    def __call__(self, predictions: torch.Tensor, targets: torch.Tensor):\n",
    "        max_values = torch.max(predictions, dim=1, keepdim=True).values\n",
    "        exp_values = torch.exp(predictions - max_values)\n",
    "        softmax_output = exp_values / torch.sum(exp_values, dim=1, keepdim=True)\n",
    "        log_probs = torch.log(softmax_output)\n",
    "        \n",
    "        nll_loss = -torch.sum(targets * log_probs, dim=1)\n",
    "        average_loss = torch.mean(nll_loss)\n",
    "        return average_loss\n",
    "\n",
    "        \n",
    "# 测试\n",
    "input = torch.randn(3, 5, requires_grad=True)\n",
    "target = torch.randn(3, 5).softmax(dim=1).argmax(1)\n",
    "target = torch.nn.functional.one_hot(target, num_classes=5).to(dtype=torch.float32)\n",
    "print(f\"输入:\\n{input}\")\n",
    "print(f\"标签:\\n{target}\")\n",
    "\n",
    "my_crossentropyloss = My_CrossEntropyLoss()\n",
    "my_loss = my_crossentropyloss(input, target)\n",
    "print(\"My_CrossEntropyLoss损失值:\", my_loss.item())\n",
    "\n",
    "nn_crossentropyloss = nn.CrossEntropyLoss()\n",
    "nn_loss = nn_crossentropyloss(input, target)\n",
    "print(\"nn.CrossEntropyLoss损失值:\", nn_loss.item())"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "dbf78501-f5be-4008-986c-d331d531491f",
   "metadata": {},
   "source": [
    "手动实现Flatten。\n",
    "\n",
    "原理很简单,就是把多维的张量拉直成一个向量。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "id": "74322629-8325-4823-b80f-f28182d577c1",
   "metadata": {},
   "outputs": [],
   "source": [
    "class My_Flatten:\n",
    "    def __call__(self, x: torch.Tensor):\n",
    "        return self.forward(x)\n",
    "\n",
    "    def forward(self, x: torch.Tensor):\n",
    "        x = x.view(x.shape[0], -1)\n",
    "        return x"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "35aee905-ae37-4faa-a7f1-a04cd8579f78",
   "metadata": {},
   "source": [
    "手动实现softmax回归模型。\n",
    "\n",
    "模型很简单,主要由一个Flatten层和一个线性层组成。\n",
    "\n",
    "Flatten层主要用于将2维的图像展开,直接作为1维的特征量输入网络。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "id": "bb31a75e-464c-4b94-b927-b219a765e35d",
   "metadata": {},
   "outputs": [],
   "source": [
    "class Model_3_1:\n",
    "    def __init__(self, num_classes):\n",
    "        self.flatten = My_Flatten()\n",
    "        self.linear = My_Linear(28 * 28, num_classes)\n",
    "        self.params = self.linear.params\n",
    "\n",
    "    def __call__(self, x: torch.Tensor):\n",
    "        return self.forward(x)\n",
    "\n",
    "    def forward(self, x: torch.Tensor):\n",
    "        x = self.flatten(x)\n",
    "        x = self.linear(x)\n",
    "        return x\n",
    "\n",
    "    def to(self, device: str):\n",
    "        for param in self.params:\n",
    "            param.data = param.data.to(device=device)\n",
    "        return self\n",
    "\n",
    "    def parameters(self):\n",
    "        return self.params"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "17e686d1-9c9a-4727-8fdc-9990d348c523",
   "metadata": {},
   "source": [
    "训练与测试过程与之前手动实现的几乎一致。由于数据集的变化,对应超参数也进行了调整。\n",
    "\n",
    "数据集也使用了现成的FashionMNIST数据集,且划分了训练集和测试集。\n",
    "\n",
    "FashionMNIST数据集直接调用API获取。数据集的image为28*28的单通道灰白图片,label为单个数值标签。\n",
    "\n",
    "训练softmax回归模型。\n",
    "进行如下步骤:\n",
    "1. 初始化超参数\n",
    "2. 获取数据集\n",
    "3. 初始化模型\n",
    "4. 定义损失函数和优化器\n",
    "5. 训练\n",
    "    1. 从训练dataloader中获取批量数据\n",
    "    2. 传入模型\n",
    "    3. 使用损失函数计算与ground_truth的损失\n",
    "    4. 使用优化器进行反向传播\n",
    "    5. 循环以上步骤\n",
    "6. 测试\n",
    "    1. 从测试dataloader中获取批量数据\n",
    "    2. 传入模型\n",
    "    3. 将预测值与ground_truth进行比较,得出正确率\n",
    "    4. 对整个训练集统计正确率,从而分析训练效果"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "id": "d816dae1-5fbe-4c29-9597-19d66b5eb6b4",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Epoch 1/10, Loss: nan, Acc: 0.09999999403953552\n",
      "Epoch 2/10, Loss: nan, Acc: 0.09999999403953552\n",
      "Epoch 3/10, Loss: nan, Acc: 0.09999999403953552\n",
      "Epoch 4/10, Loss: nan, Acc: 0.09999999403953552\n",
      "Epoch 5/10, Loss: nan, Acc: 0.09999999403953552\n",
      "Epoch 6/10, Loss: nan, Acc: 0.09999999403953552\n",
      "Epoch 7/10, Loss: nan, Acc: 0.09999999403953552\n",
      "Epoch 8/10, Loss: nan, Acc: 0.09999999403953552\n",
      "Epoch 9/10, Loss: nan, Acc: 0.09999999403953552\n",
      "Epoch 10/10, Loss: nan, Acc: 0.09999999403953552\n"
     ]
    }
   ],
   "source": [
    "learning_rate = 5e-3\n",
    "num_epochs = 10\n",
    "batch_size = 4096\n",
    "num_classes = 10\n",
    "device = \"cuda:0\" if torch.cuda.is_available() else \"cpu\"\n",
    "\n",
    "transform = transforms.Compose(\n",
    "    [\n",
    "        transforms.ToTensor(),\n",
    "        transforms.Normalize((0.5,), (0.5,)),\n",
    "    ]\n",
    ")\n",
    "train_dataset = datasets.FashionMNIST(root=\"./dataset\", train=True, transform=transform, download=True)\n",
    "test_dataset = datasets.FashionMNIST(root=\"./dataset\", train=False, transform=transform, download=True)\n",
    "train_loader = DataLoader(\n",
    "    dataset=train_dataset, batch_size=batch_size,\n",
    "    shuffle=True, num_workers=4, pin_memory=True,\n",
    ")\n",
    "test_loader = DataLoader(\n",
    "    dataset=test_dataset, batch_size=batch_size,\n",
    "    shuffle=True, num_workers=4, pin_memory=True,\n",
    ")\n",
    "\n",
    "model = Model_3_1(num_classes).to(device)\n",
    "criterion = My_CrossEntropyLoss()\n",
    "optimizer = My_optimizer(model.parameters(), lr=learning_rate)\n",
    "\n",
    "for epoch in range(num_epochs):\n",
    "    total_epoch_loss = 0\n",
    "    for images, targets in train_loader:\n",
    "        optimizer.zero_grad()\n",
    "\n",
    "        images = images.to(device)\n",
    "        targets = targets.to(device).to(dtype=torch.long)\n",
    "\n",
    "        one_hot_targets = (\n",
    "            my_one_hot(targets, num_classes=num_classes)\n",
    "            .to(device)\n",
    "            .to(dtype=torch.long)\n",
    "        )\n",
    "\n",
    "        outputs = model(images)\n",
    "        loss = criterion(outputs, one_hot_targets)\n",
    "        total_epoch_loss += loss\n",
    "\n",
    "        loss.backward()\n",
    "        optimizer.step()\n",
    "\n",
    "    total_acc = 0\n",
    "    with torch.no_grad():\n",
    "        for image, targets in test_loader:\n",
    "            image = image.to(device)\n",
    "            targets = targets.to(device)\n",
    "            outputs = model(image)\n",
    "            total_acc += (outputs.argmax(1) == targets).sum()\n",
    "    print(\n",
    "        f\"Epoch {epoch + 1}/{num_epochs}, Loss: {total_epoch_loss}, Acc: {total_acc / len(test_dataset)}\"\n",
    "    )"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a49d0165-aeb7-48c0-9b67-956bb08cb356",
   "metadata": {},
   "source": [
    "这里发现梯度爆炸。暂时无法解决。"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "3ef5240f-8a11-4678-bfce-f1cbc7e71b77",
   "metadata": {},
   "source": [
    "## 问题2\n",
    "\n",
    "**利用torch.nn实现softmax回归在Fashion-MNIST数据集上进行训练和测试,并从loss,训练集以及测试集上的准确率等多个角度对结果进行分析**"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "5c4a88c6-637e-4af5-bed5-f644685dcabc",
   "metadata": {},
   "source": [
    "使用torch.nn实现模型。\n",
    "\n",
    "将之前的Model_3_1中的手动实现函数改为torch.nn内置函数即可,再加上继承nn.Module以使用torch.nn内置模型模板特性。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "id": "0163b9f7-1019-429c-8c29-06436d0a4c98",
   "metadata": {},
   "outputs": [],
   "source": [
    "class Model_3_2(nn.Module):\n",
    "    def __init__(self, num_classes):\n",
    "        super(Model_3_2, self).__init__()\n",
    "        self.flatten = nn.Flatten()\n",
    "        self.linear = nn.Linear(28 * 28, num_classes)\n",
    "\n",
    "    def forward(self, x: torch.Tensor):\n",
    "        x = self.flatten(x)\n",
    "        x = self.linear(x)\n",
    "        return x"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "6e765ad7-c1c6-4166-bd7f-361666bd4016",
   "metadata": {},
   "source": [
    "训练与测试过程与之前手动实现的几乎一致。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "id": "a58a23e1-368c-430a-ad62-0e256dff564d",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Epoch 1/10, Loss: 15.148970603942871, Acc: 0.7520999908447266\n",
      "Epoch 2/10, Loss: 9.012335777282715, Acc: 0.7996999621391296\n",
      "Epoch 3/10, Loss: 7.9114227294921875, Acc: 0.8095999956130981\n",
      "Epoch 4/10, Loss: 7.427404403686523, Acc: 0.8215999603271484\n",
      "Epoch 5/10, Loss: 7.084254264831543, Acc: 0.8277999758720398\n",
      "Epoch 6/10, Loss: 6.885956287384033, Acc: 0.8274999856948853\n",
      "Epoch 7/10, Loss: 6.808426380157471, Acc: 0.8327999711036682\n",
      "Epoch 8/10, Loss: 6.647855758666992, Acc: 0.8323000073432922\n",
      "Epoch 9/10, Loss: 6.560361862182617, Acc: 0.8317999839782715\n",
      "Epoch 10/10, Loss: 6.5211310386657715, Acc: 0.8349999785423279\n"
     ]
    }
   ],
   "source": [
    "learning_rate = 5e-3\n",
    "num_epochs = 10\n",
    "batch_size = 4096\n",
    "num_classes = 10\n",
    "device = \"cuda:0\" if torch.cuda.is_available() else \"cpu\"\n",
    "\n",
    "transform = transforms.Compose(\n",
    "    [\n",
    "        transforms.ToTensor(),\n",
    "        transforms.Normalize((0.5,), (0.5,)),\n",
    "    ]\n",
    ")\n",
    "train_dataset = datasets.FashionMNIST(\n",
    "    root=\"./dataset\", train=True, transform=transform, download=True\n",
    ")\n",
    "test_dataset = datasets.FashionMNIST(\n",
    "    root=\"./dataset\", train=False, transform=transform, download=True\n",
    ")\n",
    "train_loader = DataLoader(\n",
    "    dataset=train_dataset,\n",
    "    batch_size=batch_size,\n",
    "    shuffle=True,\n",
    "    num_workers=4,\n",
    "    pin_memory=True,\n",
    ")\n",
    "test_loader = DataLoader(\n",
    "    dataset=test_dataset,\n",
    "    batch_size=batch_size,\n",
    "    shuffle=True,\n",
    "    num_workers=4,\n",
    "    pin_memory=True,\n",
    ")\n",
    "\n",
    "model = Model_3_2(num_classes).to(device)\n",
    "criterion = nn.CrossEntropyLoss()\n",
    "optimizer = torch.optim.Adam(model.parameters(), lr=learning_rate)\n",
    "\n",
    "for epoch in range(num_epochs):\n",
    "    total_epoch_loss = 0\n",
    "    model.train()\n",
    "    for images, targets in train_loader:\n",
    "        optimizer.zero_grad()\n",
    "\n",
    "        images = images.to(device)\n",
    "        targets = targets.to(device)\n",
    "\n",
    "        one_hot_targets = (\n",
    "            torch.nn.functional.one_hot(targets, num_classes=num_classes)\n",
    "            .to(device)\n",
    "            .to(dtype=torch.float32)\n",
    "        )\n",
    "\n",
    "        outputs = model(images)\n",
    "        loss = criterion(outputs, one_hot_targets)\n",
    "        total_epoch_loss += loss\n",
    "\n",
    "        loss.backward()\n",
    "        optimizer.step()\n",
    "\n",
    "    model.eval()\n",
    "    total_acc = 0\n",
    "    with torch.no_grad():\n",
    "        for image, targets in test_loader:\n",
    "            image = image.to(device)\n",
    "            targets = targets.to(device)\n",
    "            outputs = model(image)\n",
    "            total_acc += (outputs.argmax(1) == targets).sum()\n",
    "    print(\n",
    "        f\"Epoch {epoch + 1}/{num_epochs}, Loss: {total_epoch_loss}, Acc: {total_acc / len(test_dataset)}\"\n",
    "    )"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "59555b67-1650-4e1a-a98e-7906878bf3d0",
   "metadata": {},
   "source": [
    "与手动实现的softmax回归相比较,nn.CrossEntropyLoss比手动实现的My_CrossEntropyLoss更加稳定,没有出现梯度爆炸的情况。"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "f40431f2-e77b-4ead-81a3-ff6451a8e452",
   "metadata": {},
   "source": [
    "**实验心得体会**\n",
    "\n",
    "通过完成本次Pytorch基本操作实验,让我对Pytorch框架有了更加深入的理解。我接触深度学习主要是在大语言模型领域,比较熟悉微调大模型,但是涉及到底层的深度学习知识,我还有很多短板和不足。这次实验对我这方面的锻炼让我收获良多。\n",
    "\n",
    "首先是数据集的设置。如果数据没有进行归一化,很容易出现梯度爆炸。这是在我以前直接使用图片数据集的经历中没有遇到过的问题。\n",
    "\n",
    "在实现logistic回归模型时,通过手动实现各个组件如优化器、线性层等,让我对这些模块的工作原理有了更清晰的认识。尤其是在实现广播机制时,需要充分理解张量操作的维度变换规律。而使用Pytorch内置模块进行实现时,通过继承nn.Module可以自动获得許多功能,使代码更加简洁。\n",
    "\n",
    "在实现softmax回归时,则遇到了更大的困难。手动实现的模型很容易出现梯度爆炸的问题,而使用Pytorch内置的损失函数和优化器则可以稳定训练。这让我意识到了选择合适的优化方法的重要性。另外,Pytorch强大的自动微分机制也是构建深度神经网络的重要基础。\n",
    "\n",
    "通过这个实验,让我对Pytorch框架有了更加直观的感受,也让我看到了仅靠基础模块搭建复杂模型的难点所在。这些经验对我后续使用Pytorch构建数据集模型会很有帮助。"
   ]
  }
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