Neural network with pytorch

# TODO: Define your network architecture here
import torch
from torch import nn
from torch import optim
from torchvision import datasets, transforms
import helper

# Define a transform to normalize the data
transform = transforms.Compose([transforms.ToTensor(),
                                transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))])
# Download and load the training data
trainset = datasets.FashionMNIST('~/.pytorch/F_MNIST_data/', download=True, train=True, transform=transform)
trainloader = torch.utils.data.DataLoader(trainset, batch_size=64, shuffle=True)

images, labels = next(iter(trainloader))
images.resize_(64, 784)

model = nn.Sequential(nn.Linear(784, 128),
                      nn.ReLU(),
                      nn.Linear(128, 64),
                      nn.ReLU(),
                      nn.Linear(64, 10),
                      nn.LogSoftmax(dim=1))

criterion = nn.CrossEntropyLoss()
optimizer = optim.SGD(model.parameters(), lr=0.003)

epochs = 50
for e in range(epochs):
    running_loss = 0
    for images, labels in trainloader:
        # Flatten MNIST images into a 784 long vector
        images = images.view(images.shape[0], -1)
    
        # TODO: Training pass
        optimizer.zero_grad()
        logits = model(images)
        loss = criterion(logits, labels)
        loss.backward()
        optimizer.step()
        
        running_loss += loss.item()
    else:
        print(f"Step {e} => Training loss: {running_loss/len(trainloader)}")
        
# Use the training

%matplotlib inline
%config InlineBackend.figure_format = 'retina'

import helper
import torch.nn.functional as F

# Test out your network!

dataiter = iter(testloader)
images, labels = dataiter.next()
img = images[0]
# Convert 2D image to 1D vector
img = img.resize_(1, 784)

# TODO: Calculate the class probabilities (softmax) for img
with torch.no_grad():
    logits = model.forward(img)

# Output of the network are logits, need to take softmax for probabilities
ps = F.softmax(logits, dim=1)

# Plot the image and probabilities
helper.view_classify(img.resize_(1, 28, 28), ps, version='Fashion')