The aim of this module is to introduce you to designing simple neural networks. You've already seen how to load data in PyTorch and a sample script of the overall workflow. In this notebook, you'll implement your own neural network and report on it's performance.
We'll use the dataloading module we developed earlier.
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import sys, os
import pickle
import torch
import torch.utils.data as data
import glob
from PIL import Image
import numpy as np
def unpickle(fname):
with open(fname, 'rb') as f:
Dict = pickle.load(f, encoding='bytes')
return Dict
def load_data(batch):
print ("Loading batch:{}".format(batch))
return unpickle(batch)
class CIFARLoader(data.Dataset):
"""
CIFAR-10 Loader: Loads the CIFAR-10 data according to an index value
and returns the data and the labels.
args:
root: Root of the data directory.
Optional args:
transforms: The transforms you wish to apply to the data.
target_transforms: The transforms you wish to apply to the labels.
"""
def __init__(self, root, train=True, transform=None, target_transform=None):
self.root = root
self.transform = transform
self.target_transform = target_transform
self.train = train
patt = os.path.join(self.root, 'data_batch_*') # create the pattern we want to search for.
self.batches = sorted(glob.glob(patt))
self.train_data = []
self.train_labels = []
self.test_data = []
self.test_labels = []
if self.train:
for batch in self.batches:
entry = {}
entry = load_data(batch)
self.train_data.append(entry[b'data'])
self.train_labels += entry[b'labels']
else:
entry = load_data(os.path.join(self.root, 'test_batch'))
self.test_data.append(entry[b'data'])
self.test_labels += entry[b'labels']
#############################################
# We need to "concatenate" all the different #
# training samples into one big array. For #
# doing that we're going to use a numpy #
# function called "concatenate". #
##############################################
if self.train:
self.train_data = np.concatenate(self.train_data)
self.train_data = self.train_data.reshape((50000, 3, 32,32))
self.train_data = self.train_data.transpose((0,2,3,1)) # pay attention to this step!
else:
self.test_data = np.concatenate(self.test_data)
self.test_data = self.test_data.reshape((10000, 3,32,32))
self.test_data = self.test_data.transpose((0,2,3,1))
def __getitem__(self, index):
if self.train:
image = self.train_data[index]
label = self.train_labels[index]
else:
image = self.test_data[index]
label = self.test_labels[index]
if self.transform is not None:
image = self.transform(image)
if self.target_transform is not None:
label = self.target_transform(label)
# print(image.size())
return image, label
def __len__(self):
if self.train:
return len(self.train_data)
else:
return len(self.test_data)
Given the dataset, let's test our dataset by seeing some of the images and their corresponding labels. PyTorch provides us with a neat little function called make_grid which plots "x" number of images together in a grid.
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import torchvision.transforms as transforms
import torch.utils.data as data
import numpy as np
import matplotlib.pyplot as plt
import torchvision
def imshow(torch_tensor):
torch_tensor = torch_tensor/2 + 0.5
npimg = torch_tensor.numpy()
plt.imshow(npimg.transpose(1,2,0))
plt.show()
tfs = transforms.Compose([transforms.ToTensor(),
transforms.Normalize((0.5,0.5,0.5), (0.5,0.5,0.5))])
root='/home/akulshr/cifar-10-batches-py/'
cifar_train = CIFARLoader(root, train=True, transform=tfs) # create a "CIFARLoader instance".
cifar_loader = data.DataLoader(cifar_train, batch_size=4, shuffle=True, num_workers=2)
# all possible classes in the CIFAR-10 dataset
classes = ('plane', 'car', 'bird', 'cat',
'deer', 'dog', 'frog', 'horse', 'ship', 'truck')
data_iter = iter(cifar_loader)
data,label = data_iter.next()
#visualize data.
imshow(torchvision.utils.make_grid(data))
# print the labels
' '.join(classes[label[j]] for j in range(4))
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Now that we're through with the boring part, let's move on to the fun stuff! In the code stub being provided you can write your own network definition and then print it. We've not covered Convolutional Layers yet, so the fun will be limited to just using Linear Layers. When using linear layers keep in mind that the input features are 3*32*32. When writing out the layers it is important to think in terms of matrix multiplication. So if your input features are of dimension 4x3x32x32 then your input features must be the same dimensions. I'll define some terms so that you can use them while designing the net:
Your input to a network is usually NxCxHxW. Now a linear layer expects a single number as an input feature, so for a batch size of 1 your input features will be 3072(3*32*32).
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import torch.nn as nn
class MyNet(nn.Module):
"""
Your neural network here.
bs: Batch size, you can include
or leave it out.
"""
def __init__(self, bs):
super(MyNet, self).__init__()
pass
def forward(self, x):
pass
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net = MyNet(4) # be sure to put any additional parameters you pass to __init__ here
print(net)
Having defined our network and tested that our dataloader works to our satisfaction, we're going to train the network. For your convenience, the training script is included and it is highly recommended that you try to gain a sense of what's happening. We'll talk more about training in the coming meetings.
In [90]:
import torch.optim as optim
import torch.utils.data as data
from torch.autograd import Variable
tfs = transforms.Compose([transforms.ToTensor(),
transforms.Normalize((0.5,0.5,0.5), (0.5,0.5,0.5))])
root='/home/akulshr/cifar-10-batches-py/'
cifar_train = CIFARLoader(root, transform=tfs) # create a "CIFARLoader instance".
cifar_train_loader = data.DataLoader(cifar_train, batch_size=4, shuffle=True, num_workers=2)
lossfn = nn.NLLLoss()
optimz = optim.SGD(net.parameters(), lr=1e-3, momentum=0.9)
def train(net):
net.train()
for ep in range(2):
running_loss = 0.0
for ix, (img,label) in enumerate(cifar_train_loader, 0):
img_var = Variable(img)
label_var = Variable(label)
optimz.zero_grad()
# print(img_var.size())
op = net(img_var)
loss = lossfn(op, label_var)
loss.backward()
optimz.step()
running_loss += loss.data[0]
if ix%2000 == 1999:
print("[%d/%5d] Loss: %f"%(ep+1, ix+1, running_loss/2000))
running_loss = 0.0
print("Finished Training\n")
In [91]:
train(net)
So far we've trained the network and we're seeing some output loss. However, that's only the part of the story, since we need the model to perform well on unseen inputs. In order to do that we'll evaluate the dataset on the test_batch.
In [93]:
def imshow(torch_tensor):
torch_tensor = torch_tensor/2 + 0.5
npimg = torch_tensor.numpy()
plt.imshow(npimg.transpose(1,2,0))
plt.show()
tfs = transforms.Compose([transforms.ToTensor(),
transforms.Normalize((0.5,0.5,0.5), (0.5,0.5,0.5))])
root='/home/akulshr/cifar-10-batches-py/'
cifar_test = CIFARLoader(root, train=False, transform=tfs)
cifar_test_loader = data.DataLoader(cifar_test,batch_size=4, shuffle=False, num_workers=2)
# all possible classes in the CIFAR-10 dataset
classes = ('plane', 'car', 'bird', 'cat',
'deer', 'dog', 'frog', 'horse', 'ship', 'truck')
data_iter = iter(cifar_test_loader)
imgs,label = data_iter.next()
# Show the test images.
imshow(torchvision.utils.make_grid(imgs))
# Print the "Ground Truth labels"
print("Ground Truth: ")
print(' '.join(classes[label[j]] for j in range(4)))
So we've got these images along with their labels as "ground truth". Now let's ask the neural network we just trained as to what it thinks the images are
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data_iter = iter(cifar_test_loader)
imgs,label = data_iter.next()
op = net(Variable(imgs))
_, pred = torch.max(op.data, 1)
print("Guessed class: ")
print(' '.join(classes[pred[j]] for j in range(4)))
Pretty sweet! our neural network seems to have learnt something. Let's see how it does on the overall dataset:
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correct = 0.0
total = 0.0
for cache in cifar_test_loader:
img, label = cache
op = net(Variable(img))
_, pred = torch.max(op.data, 1)
total += label.size(0)
correct += (pred==label).sum()
print("accuracy: %f"%(100*(correct/total)))
Try out different combinations of neural network layers (limited to Linear, Softmax for now) and report on how the accuracy changes. Happy deep learning!
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