# UERP_Model Changelog

## svd_model_25m.pkl (current, recommended)
- Trained on MovieLens 25M ratings (25,000,095 ratings, 162,541 users, 59,047 movies)
- SVD, n_factors=50, n_epochs=20
- RMSE: 0.7728 | MAE: 0.5832 (held-out 10% test split)
- Serving: min_rating_count=100 filter applied

## svd_model_v1.pkl (deprecated, kept for comparison)
- Trained on MovieLens-latest-small (100,836 ratings)
- RMSE: 0.8775 | MAE: 0.6742

## ncf_model_v2.keras (Stage 4 — Neural Collaborative Filtering)
- Trained on MovieLens 25M, embedding_dim=64, 3-layer MLP (256-128-64)
- RMSE: 0.8013 | MAE: 0.6030 (original 0.5-5 scale)
- Comparison: underperforms SVD baseline (RMSE 0.7728) even after tuning attempt (32-dim -> 64-dim)
- Finding consistent with Rendle et al. (RecSys 2020), "Neural Collaborative Filtering vs. 
  Matrix Factorization Revisited" — well-tuned MF/dot-product often outperforms learned-MLP 
  similarity for pure rating-prediction tasks.
- Decision: SVD remains primary CF signal for MVP serving. NCF kept as a documented 
  experiment / potential weak-signal contributor for future Stage 6 ranking ensemble.