17_优化器.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 1. 优化器"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "① 损失函数调用backward方法，就可以调用损失函数的反向传播方法，就可以求出我们需要调节的梯度，我们就可以利用我们的优化器就可以根据梯度对参数进行调整，达到整体误差降低的目的。\n",
    "\n",
    "② 梯度要清零，如果梯度不清零会导致梯度累加。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 2. 神经网络优化一轮"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
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     ]
    }
   ],
   "source": [
    "import torch\n",
    "import torchvision\n",
    "from torch import nn \n",
    "from torch.nn import Conv2d, MaxPool2d, Flatten, Linear, Sequential\n",
    "from torch.utils.data import DataLoader\n",
    "from torch.utils.tensorboard import SummaryWriter\n",
    "\n",
    "dataset = torchvision.datasets.CIFAR10(\"./dataset\",train=False,transform=torchvision.transforms.ToTensor(),download=True)       \n",
    "dataloader = DataLoader(dataset, batch_size=64,drop_last=True)\n",
    "\n",
    "class Tudui(nn.Module):\n",
    "    def __init__(self):\n",
    "        super(Tudui, self).__init__()        \n",
    "        self.model1 = Sequential(\n",
    "            Conv2d(3,32,5,padding=2),\n",
    "            MaxPool2d(2),\n",
    "            Conv2d(32,32,5,padding=2),\n",
    "            MaxPool2d(2),\n",
    "            Conv2d(32,64,5,padding=2),\n",
    "            MaxPool2d(2),\n",
    "            Flatten(),\n",
    "            Linear(1024,64),\n",
    "            Linear(64,10)\n",
    "        )\n",
    "        \n",
    "    def forward(self, x):\n",
    "        x = self.model1(x)\n",
    "        return x\n",
    "    \n",
    "loss = nn.CrossEntropyLoss() # 交叉熵    \n",
    "tudui = Tudui()\n",
    "optim = torch.optim.SGD(tudui.parameters(),lr=0.01)   # 随机梯度下降优化器\n",
    "for data in dataloader:\n",
    "    imgs, targets = data\n",
    "    outputs = tudui(imgs)\n",
    "    result_loss = loss(outputs, targets) # 计算实际输出与目标输出的差距\n",
    "    optim.zero_grad()  # 梯度清零\n",
    "    result_loss.backward() # 反向传播，计算损失函数的梯度\n",
    "    optim.step()   # 根据梯度，对网络的参数进行调优\n",
    "    print(result_loss) # 对数据只看了一遍，只看了一轮，所以loss下降不大"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 3. 神经网络优化多轮"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Files already downloaded and verified\n",
      "tensor(358.1069, grad_fn=<AddBackward0>)\n",
      "tensor(353.8411, grad_fn=<AddBackward0>)\n",
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      "tensor(227.3427, grad_fn=<AddBackward0>)\n"
     ]
    }
   ],
   "source": [
    "import torch\n",
    "import torchvision\n",
    "from torch import nn \n",
    "from torch.nn import Conv2d, MaxPool2d, Flatten, Linear, Sequential\n",
    "from torch.utils.data import DataLoader\n",
    "from torch.utils.tensorboard import SummaryWriter\n",
    "\n",
    "dataset = torchvision.datasets.CIFAR10(\"./dataset\",train=False,transform=torchvision.transforms.ToTensor(),download=True)       \n",
    "dataloader = DataLoader(dataset, batch_size=64,drop_last=True)\n",
    "\n",
    "class Tudui(nn.Module):\n",
    "    def __init__(self):\n",
    "        super(Tudui, self).__init__()        \n",
    "        self.model1 = Sequential(\n",
    "            Conv2d(3,32,5,padding=2),\n",
    "            MaxPool2d(2),\n",
    "            Conv2d(32,32,5,padding=2),\n",
    "            MaxPool2d(2),\n",
    "            Conv2d(32,64,5,padding=2),\n",
    "            MaxPool2d(2),\n",
    "            Flatten(),\n",
    "            Linear(1024,64),\n",
    "            Linear(64,10)\n",
    "        )\n",
    "        \n",
    "    def forward(self, x):\n",
    "        x = self.model1(x)\n",
    "        return x\n",
    "    \n",
    "loss = nn.CrossEntropyLoss() # 交叉熵    \n",
    "tudui = Tudui()\n",
    "optim = torch.optim.SGD(tudui.parameters(),lr=0.01)   # 随机梯度下降优化器\n",
    "for epoch in range(20):\n",
    "    running_loss = 0.0\n",
    "    for data in dataloader:\n",
    "        imgs, targets = data\n",
    "        outputs = tudui(imgs)\n",
    "        result_loss = loss(outputs, targets) # 计算实际输出与目标输出的差距\n",
    "        optim.zero_grad()  # 梯度清零\n",
    "        result_loss.backward() # 反向传播，计算损失函数的梯度\n",
    "        optim.step()   # 根据梯度，对网络的参数进行调优\n",
    "        running_loss = running_loss + result_loss\n",
    "    print(running_loss) # 对这一轮所有误差的总和"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 4. 神经网络学习率优化"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Files already downloaded and verified\n",
      "tensor(359.4722, grad_fn=<AddBackward0>)\n",
      "tensor(359.4630, grad_fn=<AddBackward0>)\n",
      "tensor(359.4630, grad_fn=<AddBackward0>)\n",
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      "tensor(359.4630, grad_fn=<AddBackward0>)\n",
      "tensor(359.4630, grad_fn=<AddBackward0>)\n",
      "tensor(359.4630, grad_fn=<AddBackward0>)\n",
      "tensor(359.4630, grad_fn=<AddBackward0>)\n",
      "tensor(359.4630, grad_fn=<AddBackward0>)\n",
      "tensor(359.4630, grad_fn=<AddBackward0>)\n"
     ]
    }
   ],
   "source": [
    "import torch\n",
    "import torchvision\n",
    "from torch import nn \n",
    "from torch.nn import Conv2d, MaxPool2d, Flatten, Linear, Sequential\n",
    "from torch.utils.data import DataLoader\n",
    "from torch.utils.tensorboard import SummaryWriter\n",
    "\n",
    "dataset = torchvision.datasets.CIFAR10(\"./dataset\",train=False,transform=torchvision.transforms.ToTensor(),download=True)       \n",
    "dataloader = DataLoader(dataset, batch_size=64,drop_last=True)\n",
    "\n",
    "class Tudui(nn.Module):\n",
    "    def __init__(self):\n",
    "        super(Tudui, self).__init__()        \n",
    "        self.model1 = Sequential(\n",
    "            Conv2d(3,32,5,padding=2),\n",
    "            MaxPool2d(2),\n",
    "            Conv2d(32,32,5,padding=2),\n",
    "            MaxPool2d(2),\n",
    "            Conv2d(32,64,5,padding=2),\n",
    "            MaxPool2d(2),\n",
    "            Flatten(),\n",
    "            Linear(1024,64),\n",
    "            Linear(64,10)\n",
    "        )\n",
    "        \n",
    "    def forward(self, x):\n",
    "        x = self.model1(x)\n",
    "        return x\n",
    "    \n",
    "loss = nn.CrossEntropyLoss() # 交叉熵    \n",
    "tudui = Tudui()\n",
    "optim = torch.optim.SGD(tudui.parameters(),lr=0.01)   # 随机梯度下降优化器\n",
    "scheduler = torch.optim.lr_scheduler.StepLR(optim, step_size=5, gamma=0.1) # 每过 step_size 更新一次优化器，更新是学习率为原来的学习率的的 0.1 倍    \n",
    "for epoch in range(20):\n",
    "    running_loss = 0.0\n",
    "    for data in dataloader:\n",
    "        imgs, targets = data\n",
    "        outputs = tudui(imgs)\n",
    "        result_loss = loss(outputs, targets) # 计算实际输出与目标输出的差距\n",
    "        optim.zero_grad()  # 梯度清零\n",
    "        result_loss.backward() # 反向传播，计算损失函数的梯度\n",
    "        optim.step()   # 根据梯度，对网络的参数进行调优\n",
    "        scheduler.step() # 学习率太小了，所以20个轮次后，相当于没走多少\n",
    "        running_loss = running_loss + result_loss\n",
    "    print(running_loss) # 对这一轮所有误差的总和"
   ]
  }
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