Build A Large Language Model From Scratch Pdf Apr 2026

A large language model is a type of neural network that is trained on vast amounts of text data to learn the patterns and structures of language. These models are typically transformer-based architectures that use self-attention mechanisms to weigh the importance of different input elements relative to each other. The goal of a language model is to predict the next word in a sequence of text, given the context of the previous words.

# Create model, optimizer, and criterion model = LanguageModel(vocab_size, embedding_dim, hidden_dim, output_dim).to(device) optimizer = optim.Adam(model.parameters(), lr=0.001) criterion = nn.CrossEntropyLoss()

if __name__ == '__main__': main()

# Define a simple language model class LanguageModel(nn.Module): def __init__(self, vocab_size, embedding_dim, hidden_dim, output_dim): super(LanguageModel, self).__init__() self.embedding = nn.Embedding(vocab_size, embedding_dim) self.rnn = nn.RNN(embedding_dim, hidden_dim, batch_first=True) self.fc = nn.Linear(hidden_dim, output_dim)

# Evaluate the model def evaluate(model, device, loader, criterion): model.eval() total_loss = 0 with torch.no_grad(): for batch in loader: input_seq = batch['input'].to(device) output_seq = batch['output'].to(device) output = model(input_seq) loss = criterion(output, output_seq) total_loss += loss.item() return total_loss / len(loader) build a large language model from scratch pdf

# Train the model def train(model, device, loader, optimizer, criterion): model.train() total_loss = 0 for batch in loader: input_seq = batch['input'].to(device) output_seq = batch['output'].to(device) optimizer.zero_grad() output = model(input_seq) loss = criterion(output, output_seq) loss.backward() optimizer.step() total_loss += loss.item() return total_loss / len(loader)

# Load data text_data = [...] vocab = {...} A large language model is a type of

# Train and evaluate model for epoch in range(epochs): loss = train(model, device, loader, optimizer, criterion) print(f'Epoch {epoch+1}, Loss: {loss:.4f}') eval_loss = evaluate(model, device, loader, criterion) print(f'Epoch {epoch+1}, Eval Loss: {eval_loss:.4f}')

def forward(self, x): embedded = self.embedding(x) output, _ = self.rnn(embedded) output = self.fc(output[:, -1, :]) return output # Create model, optimizer, and criterion model =

def __getitem__(self, idx): text = self.text_data[idx] input_seq = [] output_seq = [] for i in range(len(text) - 1): input_seq.append(self.vocab[text[i]]) output_seq.append(self.vocab[text[i + 1]]) return { 'input': torch.tensor(input_seq), 'output': torch.tensor(output_seq) }