ANLP_assignment2 / src /part2 /train.py
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"""
Part 2 Pretraining script comparing Custom Optimizers.
Evaluates validation loss and test BLEU at 0.1x dataset token checkpoints.
Produces Section 4 / Figure 2 training dynamic plots.
"""
import os
import json
import logging
from typing import Dict, Any, List, Optional, Tuple
import torch
import torch.nn as nn
from torch.utils.data import DataLoader
from tqdm import tqdm
import matplotlib.pyplot as plt
from ..part1.config import TransformerConfig
from ..part1.model import Transformer
from .optimizers import CustomAdamW, CustomAdan, CustomLion, CustomMuon, CustomSophia
from ..utils import set_seed, compute_perplexity, compute_bleu, WandbLogger
logger = logging.getLogger("Part2_Train")
def get_optimizer(
optimizer_name: str,
model: nn.Module,
lr: float = 1e-3,
weight_decay: float = 0.01
) -> torch.optim.Optimizer:
"""Instantiates custom optimizer without using any predefined torch.optim modules."""
name = optimizer_name.lower()
if name == "adamw":
return CustomAdamW(model.parameters(), lr=lr, weight_decay=weight_decay)
elif name == "adan":
return CustomAdan(model.parameters(), lr=lr, weight_decay=weight_decay)
elif name == "lion":
# Lion typically operates with 3x-10x lower lr and higher weight decay
return CustomLion(model.parameters(), lr=lr * 0.2, weight_decay=weight_decay * 5.0)
elif name == "muon":
return CustomMuon(model.parameters(), lr=lr * 2.0, fallback_lr=lr, weight_decay=weight_decay)
elif name == "sophia":
return CustomSophia(model.parameters(), lr=lr, weight_decay=weight_decay)
else:
raise ValueError(f"Unknown optimizer: {optimizer_name}")
@torch.no_grad()
def evaluate_val_and_bleu(
model: Transformer,
val_loader: DataLoader,
eval_pairs: List[Tuple[str, str]],
tokenizer: Any,
device: torch.device,
max_eval_pairs: int = 200
) -> Tuple[float, float, float]:
"""Computes validation loss, validation perplexity, and test BLEU score."""
model.eval()
total_loss = 0.0
total_tokens = 0
for batch in val_loader:
input_ids = batch["input_ids"].to(device)
targets = batch["targets"].to(device)
logits, loss, _ = model(input_ids, targets=targets)
num_tok = (targets != -100).sum().item()
total_loss += loss.item() * num_tok
total_tokens += max(num_tok, 1)
val_loss = total_loss / max(total_tokens, 1)
val_ppl = compute_perplexity(val_loss)
# Compute BLEU on prefix-continuation test pairs
preds, refs = [], []
for prompt, gold_continuation in eval_pairs[:max_eval_pairs]:
prompt_ids = tokenizer(prompt, return_tensors="pt").input_ids.to(device)
if prompt_ids.shape[1] >= model.config.N_ctx:
continue
curr_ids = prompt_ids.clone()
for _ in range(30):
if curr_ids.shape[1] >= model.config.N_ctx:
break
logits, _, _ = model(curr_ids)
next_tok = logits[:, -1, :].argmax(dim=-1, keepdim=True)
curr_ids = torch.cat([curr_ids, next_tok], dim=1)
if next_tok.item() == tokenizer.eos_token_id:
break
gen_tokens = curr_ids[0, prompt_ids.shape[1]:]
pred_text = tokenizer.decode(gen_tokens.cpu(), skip_special_tokens=True)
preds.append(pred_text)
refs.append([gold_continuation])
test_bleu = compute_bleu(preds, refs)
return val_loss, val_ppl, test_bleu
def run_optimizer_benchmark(
optimizer_names: List[str],
train_loader: DataLoader,
val_loader: DataLoader,
eval_pairs: List[Tuple[str, str]],
tokenizer: Any,
config: TransformerConfig,
total_budget_tokens: int,
device: torch.device,
checkpoints_count: int = 10,
output_dir: str = "assets/part2"
) -> Dict[str, Dict[str, List[float]]]:
"""
Trains models with different optimizers up to 1.0x total dataset tokens,
recording val loss and test BLEU at 0.1x dataset intervals (Chinchilla curve).
"""
os.makedirs(output_dir, exist_ok=True)
checkpoint_interval_tokens = total_budget_tokens // checkpoints_count
all_results: Dict[str, Dict[str, List[float]]] = {}
for opt_name in optimizer_names:
logger.info(f"--- Starting training run for Optimizer: {opt_name.upper()} ---")
set_seed(42)
model = Transformer(config).to(device)
optimizer = get_optimizer(opt_name, model, lr=config.learning_rate, weight_decay=config.weight_decay)
wandb_logger = None
if os.environ.get("WANDB_API_KEY") and os.environ.get("WANDB_MODE") != "offline":
try:
wandb_logger = WandbLogger(
project="ANLP-Assignment-2",
name=f"Part2-Opt-{opt_name}",
config={"optimizer": opt_name, "budget_tokens": total_budget_tokens}
)
except Exception as e:
logger.warning(f"Could not initialize WandB ({e}).")
tokens_seen = 0
next_checkpoint_tokens = checkpoint_interval_tokens
history: Dict[str, List[float]] = {
"tokens": [],
"val_loss": [],
"val_ppl": [],
"test_bleu": []
}
# Initial zero-shot evaluation
v_loss, v_ppl, t_bleu = evaluate_val_and_bleu(model, val_loader, eval_pairs, tokenizer, device)
history["tokens"].append(0)
history["val_loss"].append(v_loss)
history["val_ppl"].append(v_ppl)
history["test_bleu"].append(t_bleu)
if wandb_logger:
wandb_logger.log({
"tokens_seen": 0,
"val/loss": v_loss,
"val/perplexity": v_ppl,
"test/bleu": t_bleu
}, step=0)
model.train()
train_iter = iter(train_loader)
while tokens_seen < total_budget_tokens:
try:
batch = next(train_iter)
except StopIteration:
train_iter = iter(train_loader)
batch = next(train_iter)
input_ids = batch["input_ids"].to(device)
targets = batch["targets"].to(device)
optimizer.zero_grad()
logits, loss, _ = model(input_ids, targets=targets)
loss.backward()
# Sophia requires occasional hessian update
if opt_name == "sophia" and hasattr(optimizer, "update_hessian"):
optimizer.update_hessian()
optimizer.step()
batch_tokens = input_ids.numel()
tokens_seen += batch_tokens
if tokens_seen >= next_checkpoint_tokens:
v_loss, v_ppl, t_bleu = evaluate_val_and_bleu(model, val_loader, eval_pairs, tokenizer, device)
history["tokens"].append(tokens_seen)
history["val_loss"].append(v_loss)
history["val_ppl"].append(v_ppl)
history["test_bleu"].append(t_bleu)
if wandb_logger:
wandb_logger.log({
"tokens_seen": tokens_seen,
"val/loss": v_loss,
"val/perplexity": v_ppl,
"test/bleu": t_bleu
}, step=tokens_seen)
logger.info(f"[{opt_name}] Tokens: {tokens_seen}/{total_budget_tokens} | Val Loss: {v_loss:.4f} | BLEU: {t_bleu:.2f}")
next_checkpoint_tokens += checkpoint_interval_tokens
model.train()
if wandb_logger:
wandb_logger.finish()
all_results[opt_name] = history
# Save comparative plots
plot_comparative_dynamics(all_results, save_path=os.path.join(output_dir, "optimizer_dynamics.png"))
with open(os.path.join(output_dir, "optimizer_benchmark_results.json"), "w") as f:
json.dump(all_results, f, indent=2)
return all_results
def plot_comparative_dynamics(
results: Dict[str, Dict[str, List[float]]],
save_path: str = "assets/optimizer_dynamics.png"
) -> None:
"""Plots Figure 2 equivalent: Validation Loss and Test BLEU vs Tokens."""
os.makedirs(os.path.dirname(os.path.abspath(save_path)), exist_ok=True)
fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(14, 5))
for opt_name, history in results.items():
tokens = [t / 1e6 for t in history["tokens"]] # In millions of tokens
ax1.plot(tokens, history["val_loss"], marker="o", label=opt_name.upper())
ax2.plot(tokens, history["test_bleu"], marker="s", label=opt_name.upper())
ax1.set_title("Validation Loss vs Training Tokens (Figure 2 Replication)")
ax1.set_xlabel("Tokens (Millions)")
ax1.set_ylabel("Validation Loss")
ax1.legend()
ax1.grid(True, linestyle="--", alpha=0.5)
ax2.set_title("Test BLEU Score vs Training Tokens")
ax2.set_xlabel("Tokens (Millions)")
ax2.set_ylabel("BLEU Score")
ax2.legend()
ax2.grid(True, linestyle="--", alpha=0.5)
plt.tight_layout()
plt.savefig(save_path, dpi=200)
plt.close()
logger.info(f"Saved optimizer dynamics plot to {save_path}")
def run_part2_pipeline(
optimizer_names: Optional[List[str]] = None,
dataset_name: str = "browndw/human-ai-parallel-corpus",
total_budget_tokens: int = 200_000,
batch_size: int = 32,
device: Optional[torch.device] = None,
output_dir: str = "assets/part2"
) -> Dict[str, Any]:
"""
Turnkey pipeline for benchmarking custom optimizers on browndw/human-ai-parallel-corpus.
Loads data, trains models, logs intermediate 0.1x token checkpoints, and plots Chinchilla curves.
"""
from .dataset import PretrainDataset
from ..part1.dataset import build_or_load_tokenizer
os.makedirs(output_dir, exist_ok=True)
if device is None:
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
if optimizer_names is None:
optimizer_names = ["adamw", "adan", "lion", "muon", "sophia"]
config = TransformerConfig(ablation_variant="dense", D_model=256, N_ctx=128, D_ff=1024, N_layers=4)
tokenizer = build_or_load_tokenizer(vocab_size=config.N_vocab)
logger.info(f"Loading pretraining corpus: {dataset_name}...")
try:
from datasets import load_dataset
ds = load_dataset(dataset_name, split="train")
texts = []
for i, item in enumerate(ds):
if i >= 5000:
break
# Collect text fields
t = item.get("text_human") or item.get("text") or item.get("text_ai") or ""
if t:
texts.append(t)
except Exception as e:
logger.warning(f"Could not load Hugging Face dataset ({e}). Using synthetic demonstration corpus.")
texts = [
"Language models learn probabilistic distributions over sequence tokens through self-supervised pretraining.",
"Optimization trajectory depends heavily on learning rate schedules, momentum damping, and gradient geometry.",
"Second order and matrix based optimizers like Muon and Sophia provide faster loss reduction per token."
] * 300
split_idx = int(len(texts) * 0.9)
train_texts = texts[:split_idx]
val_texts = texts[split_idx:] if split_idx < len(texts) else texts[:10]
train_ds = PretrainDataset(train_texts, tokenizer, seq_len=config.N_ctx)
val_ds = PretrainDataset(val_texts, tokenizer, seq_len=config.N_ctx)
train_loader = DataLoader(train_ds, batch_size=batch_size, shuffle=True)
val_loader = DataLoader(val_ds, batch_size=batch_size, shuffle=False)
eval_pairs = val_ds.eval_pairs if len(val_ds.eval_pairs) > 0 else [
("Language models learn", "probabilistic distributions over sequence tokens."),
("Optimization trajectory depends", "heavily on learning rate schedules.")
]
results = run_optimizer_benchmark(
optimizer_names=optimizer_names,
train_loader=train_loader,
val_loader=val_loader,
eval_pairs=eval_pairs,
tokenizer=tokenizer,
config=config,
total_budget_tokens=total_budget_tokens,
device=device,
output_dir=output_dir
)
# Also copy plot to assets root
root_plot = "assets/optimizer_dynamics.png"
plot_comparative_dynamics(results, save_path=root_plot)
return results