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DFF: Decision-Focused Fine-Tuning for Smarter Predict-Then-Optimize with Limited Data
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Proposes Decision-Focused Fine-tuning (DFF), which wraps any backbone predictor with a trust-region bias correction layer (input-dependent multiplicative weights bounded by a sigmoid, residual bias zero) trained with SPO+ decision loss, to improve decision quality while bounding prediction shift under limited data.
Problem
Decision-focused learning under limited data can distort predictions away from their physical meaning (multiplicative shifts), and DFL is hard to apply to non-differentiable backbone models such as tree ensembles and simulation models in predict-then-optimize pipelines.
Approach
Fine-tune a fixed backbone prediction with an input-dependent multiplicative-plus-bias correction whose output is constrained to a percentage trust region around the original prediction (offset-scaled sigmoid), so the decision loss is optimized via SPO+ without touching the backbone's weights, and the prediction shift is theoretically bounded.
Key results
- On the synthetic benchmarks, DFF (fine-tuned 2-fold Boost) achieves the lowest NDR in most settings, e.g., 4.39% vs 4.49% for 2-fold Boost on network flow Dataset 1, and 4.81% on Dataset 2.
- On DiDi XGBoost fine-tuning, DFF reduces NDR to 2.39% (vs 2.54% XGBoost and 2.40% NN-SPO+) while keeping MSE at 0.49 (XGBoost 0.45; NN-SPO+ 2.04).
- Fine-tuning the DiDi simulation model with DFF reduces normalized decision regret by 24.37% relative to the original simulation model (2.79% to 2.11%) with MSE essentially unchanged.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Apply DFF fine-tuning to 2-fold Boost | 2-fold Boost · Network Flow Dataset 1 | NDR: 4.49% -> 4.39% | Helped |
| Apply DFF fine-tuning to 2-fold Boost | 2-fold Boost · Network Flow Dataset 2 | NDR: 4.88% -> 4.81% | Helped |
| Apply DFF fine-tuning to 2-fold Boost | 2-fold Boost · Portfolio Optimization Dataset 1 | NDR: 16.08% -> 15.97% | Hurt |
| Apply DFF fine-tuning to 2-fold Boost | 2-fold Boost · Portfolio Optimization Dataset 2 | NDR: 15.92% -> 15.91% | Helped |
| Fine-tune XGBoost using DFF | XGBoost · Ride-hailing resource allocation | NDR: 2.54% -> 2.39% | Helped |
| Fine-tune the simulation model using DFF | Simulation model · Ride-hailing resource allocation | NDR: 2.79% -> 2.11% | Helped |
| Fine-tune the simulation model using DFF | Simulation model · Ride-hailing resource allocation | MSE: 2.59 × 10^{-2} -> 2.61 × 10^{-2} | No clear effect |
| Increase the DFF trust-region parameter ε (ablation) | DFF fine-tuning of the simulation model · Ride-hailing resource allocation | MSE | Hurt |
| Increase ε above 0.2 (ablation) | DFF fine-tuning of the simulation model · Ride-hailing resource allocation | NDR | No clear effect |
Surprising findings
- Direct DL training (NN-SPO+) induced multiplicative shifts, producing unimodal predictions where the ground truth is bimodal, while DFF's predictions matched the ground truth distribution.
- On the portfolio Dataset 1, NN-MSE outperformed DFF because the trust region limits improvement over the weaker 2-fold Boost base model.
Limitations
- Constrained fine-tuning cannot exceed the trust region, so gains are limited when the backbone is weak (e.g., portfolio Dataset 1).
- Experiments use only SPO+ for gradients and a fixed epsilon of 0.5 for synthetic data; generality to other decision-loss gradient methods is only claimed.
- Extension to constraints with uncertain parameters and multi-task or multi-objective settings is left to future work.
Experimental setup
Datasets: synthetic network flow data synthetic portfolio optimization data DiDi Chuxing ride-hailing subsidy market data
Benchmarks: network flow problem portfolio optimization problem DiDi resource allocation (subsidy allocation) shortest path (predictions distribution)
Metrics: normalized decision regret (NDR) MSE RMSE increment bound cosine similarity
Baselines: Random Forest SPO Forest Boost Dboost NN-MSE NN-SPO+ 2-fold Boost XGBoost Average allocation
Builds on: SPO+ PyEPO cross-fitting hyper-network
Closest papers by meaning
- Feasibility-Aware Decision-Focused Learning for Predicting Parameters in the Constraints (NeurIPS 2025 · similarity 0.88)
- Solver-Free Decision-Focused Learning for Linear Optimization Problems (NeurIPS 2025 · similarity 0.88)
- Leaving the Nest: Going beyond Local Loss Functions for Predict-Then-Optimize (AAAI 2024 · similarity 0.85)
- Data Mixture Optimization: A Multi-fidelity Multi-scale Bayesian Framework (NeurIPS 2025 · similarity 0.85)
- Contextual Optimization Under Model Misspecification: A Tractable and Generalizable Approach (ICML 2025 · similarity 0.85)
- Locally Convex Global Loss Network for Decision-Focused Learning (AAAI 2025 · similarity 0.84)
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