Learn all the basics you need to get started with this deep learning framework! In this part we implement a logistic regression algorithm and apply all the concepts that we have learned so far:

- Training Pipeline in PyTorch
- Model Design
- Loss and Optimizer
- Automatic Training steps with forward pass, backward pass, and weight updates

All code from this course can be found on GitHub.

## Logistic Regression in PyTorch

```
import torch
import torch.nn as nn
import numpy as np
from sklearn import datasets
from sklearn.preprocessing import StandardScaler
from sklearn.model_selection import train_test_split
# 0) Prepare data
bc = datasets.load_breast_cancer()
X, y = bc.data, bc.target
n_samples, n_features = X.shape
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=1234)
# scale
sc = StandardScaler()
X_train = sc.fit_transform(X_train)
X_test = sc.transform(X_test)
X_train = torch.from_numpy(X_train.astype(np.float32))
X_test = torch.from_numpy(X_test.astype(np.float32))
y_train = torch.from_numpy(y_train.astype(np.float32))
y_test = torch.from_numpy(y_test.astype(np.float32))
y_train = y_train.view(y_train.shape[0], 1)
y_test = y_test.view(y_test.shape[0], 1)
# 1) Model
# Linear model f = wx + b , sigmoid at the end
class Model(nn.Module):
def __init__(self, n_input_features):
super(Model, self).__init__()
self.linear = nn.Linear(n_input_features, 1)
def forward(self, x):
y_pred = torch.sigmoid(self.linear(x))
return y_pred
model = Model(n_features)
# 2) Loss and optimizer
num_epochs = 100
learning_rate = 0.01
criterion = nn.BCELoss()
optimizer = torch.optim.SGD(model.parameters(), lr=learning_rate)
# 3) Training loop
for epoch in range(num_epochs):
# Forward pass and loss
y_pred = model(X_train)
loss = criterion(y_pred, y_train)
# Backward pass and update
loss.backward()
optimizer.step()
# zero grad before new step
optimizer.zero_grad()
if (epoch+1) % 10 == 0:
print(f'epoch: {epoch+1}, loss = {loss.item():.4f}')
with torch.no_grad():
y_predicted = model(X_test)
y_predicted_cls = y_predicted.round()
acc = y_predicted_cls.eq(y_test).sum() / float(y_test.shape[0])
print(f'accuracy: {acc.item():.4f}')
```