mirror of
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119 lines
3.8 KiB
Python
119 lines
3.8 KiB
Python
"""
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A simple walkthrough of how to code a convolutional neural network (CNN)
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using the PyTorch library. For demonstration we train it on the very
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common MNIST dataset of handwritten digits. In this code we go through
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how to create the network as well as initialize a loss function, optimizer,
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check accuracy and more.
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Programmed by Aladdin Persson
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* 2020-04-08: Initial coding
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* 2021-03-24: More detailed comments and small revision of the code
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"""
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# Imports
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import torch
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import torchvision # torch package for vision related things
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import torch.nn.functional as F # Parameterless functions, like (some) activation functions
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import torchvision.datasets as datasets # Standard datasets
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import torchvision.transforms as transforms # Transformations we can perform on our dataset for augmentation
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from torch import optim # For optimizers like SGD, Adam, etc.
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from torch import nn # All neural network modules
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from torch.utils.data import DataLoader # Gives easier dataset managment by creating mini batches etc.
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from tqdm import tqdm # For nice progress bar!
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# Simple CNN
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class CNN(nn.Module):
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def __init__(self, in_channels=1, num_classes=10):
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super(CNN, self).__init__()
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self.conv1 = nn.Conv2d(
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in_channels=in_channels,
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out_channels=8,
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kernel_size=(3, 3),
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stride=(1, 1),
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padding=(1, 1),
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)
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self.pool = nn.MaxPool2d(kernel_size=(2, 2), stride=(2, 2))
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self.conv2 = nn.Conv2d(
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in_channels=8,
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out_channels=16,
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kernel_size=(3, 3),
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stride=(1, 1),
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padding=(1, 1),
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)
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self.fc1 = nn.Linear(16 * 7 * 7, num_classes)
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def forward(self, x):
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x = F.relu(self.conv1(x))
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x = self.pool(x)
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x = F.relu(self.conv2(x))
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x = self.pool(x)
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x = x.reshape(x.shape[0], -1)
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x = self.fc1(x)
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return x
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# Set device
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device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
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# Hyperparameters
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in_channels = 1
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num_classes = 10
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learning_rate = 0.001
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batch_size = 64
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num_epochs = 3
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# Load Data
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train_dataset = datasets.MNIST(root="dataset/", train=True, transform=transforms.ToTensor(), download=True)
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test_dataset = datasets.MNIST(root="dataset/", train=False, transform=transforms.ToTensor(), download=True)
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train_loader = DataLoader(dataset=train_dataset, batch_size=batch_size, shuffle=True)
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test_loader = DataLoader(dataset=test_dataset, batch_size=batch_size, shuffle=True)
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# Initialize network
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model = CNN(in_channels=in_channels, num_classes=num_classes).to(device)
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# Loss and optimizer
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criterion = nn.CrossEntropyLoss()
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optimizer = optim.Adam(model.parameters(), lr=learning_rate)
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# Train Network
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for epoch in range(num_epochs):
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for batch_idx, (data, targets) in enumerate(tqdm(train_loader)):
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# Get data to cuda if possible
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data = data.to(device=device)
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targets = targets.to(device=device)
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# forward
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scores = model(data)
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loss = criterion(scores, targets)
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# backward
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optimizer.zero_grad()
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loss.backward()
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# gradient descent or adam step
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optimizer.step()
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# Check accuracy on training & test to see how good our model
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def check_accuracy(loader, model):
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num_correct = 0
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num_samples = 0
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model.eval()
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with torch.no_grad():
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for x, y in loader:
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x = x.to(device=device)
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y = y.to(device=device)
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scores = model(x)
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_, predictions = scores.max(1)
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num_correct += (predictions == y).sum()
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num_samples += predictions.size(0)
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model.train()
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return num_correct/num_samples
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print(f"Accuracy on training set: {check_accuracy(train_loader, model)*100:.2f}")
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print(f"Accuracy on test set: {check_accuracy(test_loader, model)*100:.2f}") |