diff --git a/gpt.py b/gpt.py index 81f50c42..fabe3de6 100644 --- a/gpt.py +++ b/gpt.py @@ -3,16 +3,16 @@ from torch.nn import functional as F # hyperparameters -batch_size = 64 # how many independent sequences will we process in parallel? -block_size = 256 # what is the maximum context length for predictions? +batch_size = 64 # how many independent sequences will we process in parallel? +block_size = 256 # what is the maximum context length for predictions? max_iters = 5000 eval_interval = 500 learning_rate = 3e-4 device = 'cuda' if torch.cuda.is_available() else 'cpu' eval_iters = 200 -n_embd = 384 -n_head = 6 -n_layer = 6 +n_embds = 384 +n_heads = 6 +n_layers = 6 dropout = 0.2 # ------------ @@ -26,27 +26,29 @@ chars = sorted(list(set(text))) vocab_size = len(chars) # create a mapping from characters to integers -stoi = { ch:i for i,ch in enumerate(chars) } -itos = { i:ch for i,ch in enumerate(chars) } -encode = lambda s: [stoi[c] for c in s] # encoder: take a string, output a list of integers -decode = lambda l: ''.join([itos[i] for i in l]) # decoder: take a list of integers, output a string +stoi = {ch: i for i, ch in enumerate(chars)} +itos = {i: ch for i, ch in enumerate(chars)} +encode = lambda s: [stoi[c] for c in s] # encoder: take a string, output a list of integers +decode = lambda l: ''.join([itos[i] for i in l]) # decoder: take a list of integers, output a string # Train and test splits data = torch.tensor(encode(text), dtype=torch.long) -n = int(0.9*len(data)) # first 90% will be train, rest val +n = int(0.9 * len(data)) # first 90% will be train, rest val train_data = data[:n] val_data = data[n:] + # data loading def get_batch(split): # generate a small batch of data of inputs x and targets y - data = train_data if split == 'train' else val_data - ix = torch.randint(len(data) - block_size, (batch_size,)) - x = torch.stack([data[i:i+block_size] for i in ix]) - y = torch.stack([data[i+1:i+block_size+1] for i in ix]) + phase_data = train_data if split == 'train' else val_data + ix = torch.randint(len(phase_data) - block_size, (batch_size,)) + x = torch.stack([phase_data[i:i + block_size] for i in ix]) + y = torch.stack([phase_data[i + 1:i + block_size + 1] for i in ix]) x, y = x.to(device), y.to(device) return x, y + @torch.no_grad() def estimate_loss(): out = {} @@ -54,17 +56,18 @@ def estimate_loss(): for split in ['train', 'val']: losses = torch.zeros(eval_iters) for k in range(eval_iters): - X, Y = get_batch(split) - logits, loss = model(X, Y) + inputs, outputs = get_batch(split) + logits, loss = model(inputs, outputs) losses[k] = loss.item() out[split] = losses.mean() model.train() return out + class Head(nn.Module): """ one head of self-attention """ - def __init__(self, head_size): + def __init__(self, n_embd, head_size): super().__init__() self.key = nn.Linear(n_embd, head_size, bias=False) self.query = nn.Linear(n_embd, head_size, bias=False) @@ -74,25 +77,26 @@ def __init__(self, head_size): self.dropout = nn.Dropout(dropout) def forward(self, x): - B,T,C = x.shape - k = self.key(x) # (B,T,C) - q = self.query(x) # (B,T,C) + b, t, ch = x.shape + k = self.key(x) # (B,T,C) + q = self.query(x) # (B,T,C) # compute attention scores ("affinities") - wei = q @ k.transpose(-2,-1) * C**-0.5 # (B, T, C) @ (B, C, T) -> (B, T, T) - wei = wei.masked_fill(self.tril[:T, :T] == 0, float('-inf')) # (B, T, T) - wei = F.softmax(wei, dim=-1) # (B, T, T) + wei = q @ k.transpose(-2, -1) * ch ** -0.5 # (B, T, C) @ (B, C, T) -> (B, T, T) + wei = wei.masked_fill(self.tril[:t, :t] == 0, float('-inf')) # (B, T, T) + wei = F.softmax(wei, dim=-1) # (B, T, T) wei = self.dropout(wei) # perform the weighted aggregation of the values - v = self.value(x) # (B,T,C) - out = wei @ v # (B, T, T) @ (B, T, C) -> (B, T, C) + v = self.value(x) # (B,T,C) + out = wei @ v # (B, T, T) @ (B, T, C) -> (B, T, C) return out + class MultiHeadAttention(nn.Module): """ multiple heads of self-attention in parallel """ - def __init__(self, num_heads, head_size): + def __init__(self, n_embd, num_heads, head_size): super().__init__() - self.heads = nn.ModuleList([Head(head_size) for _ in range(num_heads)]) + self.heads = nn.ModuleList([Head(n_embd, head_size) for _ in range(num_heads)]) self.proj = nn.Linear(n_embd, n_embd) self.dropout = nn.Dropout(dropout) @@ -101,6 +105,7 @@ def forward(self, x): out = self.dropout(self.proj(out)) return out + class FeedFoward(nn.Module): """ a simple linear layer followed by a non-linearity """ @@ -116,6 +121,7 @@ def __init__(self, n_embd): def forward(self, x): return self.net(x) + class Block(nn.Module): """ Transformer block: communication followed by computation """ @@ -123,7 +129,7 @@ def __init__(self, n_embd, n_head): # n_embd: embedding dimension, n_head: the number of heads we'd like super().__init__() head_size = n_embd // n_head - self.sa = MultiHeadAttention(n_head, head_size) + self.sa = MultiHeadAttention(n_embd, n_head, head_size) self.ffwd = FeedFoward(n_embd) self.ln1 = nn.LayerNorm(n_embd) self.ln2 = nn.LayerNorm(n_embd) @@ -133,35 +139,36 @@ def forward(self, x): x = x + self.ffwd(self.ln2(x)) return x + # super simple bigram model class BigramLanguageModel(nn.Module): - def __init__(self): + def __init__(self, n_embd, n_head, n_layer): super().__init__() # each token directly reads off the logits for the next token from a lookup table self.token_embedding_table = nn.Embedding(vocab_size, n_embd) self.position_embedding_table = nn.Embedding(block_size, n_embd) self.blocks = nn.Sequential(*[Block(n_embd, n_head=n_head) for _ in range(n_layer)]) - self.ln_f = nn.LayerNorm(n_embd) # final layer norm + self.ln_f = nn.LayerNorm(n_embd) # final layer norm self.lm_head = nn.Linear(n_embd, vocab_size) def forward(self, idx, targets=None): - B, T = idx.shape + b, t = idx.shape # idx and targets are both (B,T) tensor of integers - tok_emb = self.token_embedding_table(idx) # (B,T,C) - pos_emb = self.position_embedding_table(torch.arange(T, device=device)) # (T,C) - x = tok_emb + pos_emb # (B,T,C) - x = self.blocks(x) # (B,T,C) - x = self.ln_f(x) # (B,T,C) - logits = self.lm_head(x) # (B,T,vocab_size) + tok_emb = self.token_embedding_table(idx) # (B,T,C) + pos_emb = self.position_embedding_table(torch.arange(t, device=device)) # (T,C) + x = tok_emb + pos_emb # (B,T,C) + x = self.blocks(x) # (B,T,C) + x = self.ln_f(x) # (B,T,C) + logits = self.lm_head(x) # (B,T,vocab_size) if targets is None: loss = None else: - B, T, C = logits.shape - logits = logits.view(B*T, C) - targets = targets.view(B*T) + b, t, ch = logits.shape + logits = logits.view(b * t, ch) + targets = targets.view(b * t) loss = F.cross_entropy(logits, targets) return logits, loss @@ -174,40 +181,40 @@ def generate(self, idx, max_new_tokens): # get the predictions logits, loss = self(idx_cond) # focus only on the last time step - logits = logits[:, -1, :] # becomes (B, C) + logits = logits[:, -1, :] # becomes (B, C) # apply softmax to get probabilities - probs = F.softmax(logits, dim=-1) # (B, C) + probs = F.softmax(logits, dim=-1) # (B, C) # sample from the distribution - idx_next = torch.multinomial(probs, num_samples=1) # (B, 1) + idx_next = torch.multinomial(probs, num_samples=1) # (B, 1) # append sampled index to the running sequence - idx = torch.cat((idx, idx_next), dim=1) # (B, T+1) + idx = torch.cat((idx, idx_next), dim=1) # (B, T+1) return idx -model = BigramLanguageModel() + +model = BigramLanguageModel(n_embds, n_heads, n_layers) m = model.to(device) # print the number of parameters in the model -print(sum(p.numel() for p in m.parameters())/1e6, 'M parameters') +print(sum(p.numel() for p in m.parameters()) / 1e6, 'M parameters') # create a PyTorch optimizer optimizer = torch.optim.AdamW(model.parameters(), lr=learning_rate) -for iter in range(max_iters): - +for i_iter in range(max_iters): # every once in a while evaluate the loss on train and val sets - if iter % eval_interval == 0 or iter == max_iters - 1: - losses = estimate_loss() - print(f"step {iter}: train loss {losses['train']:.4f}, val loss {losses['val']:.4f}") + if i_iter % eval_interval == 0 or i_iter == max_iters - 1: + estimated_losses = estimate_loss() + print(f"step {i_iter}: train loss {estimated_losses['train']:.4f}, val loss {estimated_losses['val']:.4f}") # sample a batch of data xb, yb = get_batch('train') # evaluate the loss - logits, loss = model(xb, yb) + output_logits, output_loss = model(xb, yb) optimizer.zero_grad(set_to_none=True) - loss.backward() + output_loss.backward() optimizer.step() # generate from the model context = torch.zeros((1, 1), dtype=torch.long, device=device) print(decode(m.generate(context, max_new_tokens=500)[0].tolist())) -#open('more.txt', 'w').write(decode(m.generate(context, max_new_tokens=10000)[0].tolist())) +# open('more.txt', 'w').write(decode(m.generate(context, max_new_tokens=10000)[0].tolist()))