Optimizing high-dimensional physical systems under expensive evaluations and complex constraints is a central challenge in science and engineering. In offline model-based optimization (MBO), methods must improve designs using only a fixed dataset and no test-time access to the true objective. However, existing methods typically suffer from conservatism, unconstrained surrogate exploitation, or function as static inference-time samplers that cannot refine candidates against precise physical objectives. In this paper, we propose Differentiable Diffusion Conditioning (D2C) for offline MBO, which leverages the fact that deterministic sampling makes the reverse denoising chain differentiable with respect to the conditioning signal. D2C turns a frozen conditional diffusion model into an end-to-end gradient-based optimizer by directly optimizing conditioning variables at test time via gradients from frozen surrogate objectives and physics-informed penalties backpropagated through the reverse chain. We implement this idea in a composed proposer-evaluator framework and evaluate it on laser pulse optimization for inertial confinement fusion, sustainable data-center workload scheduling, and four Design-Bench tasks. Our method achieves the strongest results on the two real-world tasks and the best average rank across four Design-Bench tasks.
Figures & tables
Figure 1: Overview of D2C. A frozen conditional diffusion proposer generates designs from conditioning inputs, a frozen surrogate evaluator and physics-informed penalties define a differentiable test-time objective, and gradients are backpropagated through the deterministic DDIM chain to optimize the conditioning signal. Multiple noise trials and loss-weight samples produce a candidate pool, from which the best valid design is selected after domain-specific constraint checks.
Method
ICF Standard
ICF Top
DC
Gradient Ascent
2.31%±0.31
1.46%±0.29
0.14%±0.04
COMs
3.14%±0.41
0.43%±0.11
1.33%±0.24
BDI
2.42%±0.37
1.33%±0.21
0.37%±0.08
CbAS
4.49%±0.63
1.86%±0.29
1.85%±0.31
MINs
3.71%±0.67
1.51%±0.43
1.21%±0.23
REINFORCE
3.50%±0.56
0.32%±0.08
1.26%±0.25
Table 1: Real-world physical design tasks. Values are mean percentage improvement (%) over the baseline design ± std over 5 runs. Bold : best.
Method
TF Bind 8
TF Bind 10
D’Kitty
Ant
Avg. Rank
D (best)
0.439
0.467
0.884
0.565
–
Gradient Ascent
0.854±0.029
0.575±0.039
0.937±0.014
0.749±0.034
10.38
COMs
0.949±0.018
0.598±0.034
0.935±0.013
0.863±0.021
6.75
BDI
0.969±0.012
0.609±0.026
0.931±0.014
0.717±0.032
7.00
CbAS
0.918±0.027
0.607±0.032
0.908±0.017
0.672±0.035
11.25
MINs
0.923±0.026
0.625±0.033
0.917±0.017
0.806±0.030
8.50
Table 2: Design-Bench tasks. 100th-percentile normalized score ± std over 5 runs. The row D (best) reports the best design present in the offline dataset for each task. Scores above D (best) therefore indicate improvement beyond the best offline example under the evaluation protocol used for that column. Avg. Rank is the mean ordinal rank across all four tasks ( ↓ lower is better). Bold : best per column.
Appendix figures & tables14 assets
Supplementary material from the paper’s appendix.
Appendix
Hyperparameter
ICF
DC
Hidden dimension H
1024
1024
Residual blocks L
6
6
Dropout
0.1
0.1
CFG dropout pdrop
0.1
0.1
EMA decay β
0.9999
0.9999
Learning rate
5×10−5
5×10−5
Appendix
Table 3: Training hyperparameters for the diffusion proposer.
Table 5: Training hyperparameters for the surrogate evaluator Sϕ .
Hyperparameter
Value
Optimized variable
Initial latent/noise vector z (same dimension as x )
Fixed conditioning target
c=1.0
Optimizer
Adam
Learning rate
1×10−2
Optimization steps
100
DDIM inference steps
50
Appendix
Table 6: D2C inference-time hyperparameters for Design-Bench. These settings are shared across TF Bind 8, TF Bind 10, Ant Morphology, and D'Kitty Morphology unless noted otherwise.
Task
w=0
w=0.5
w=1
w=2
w=3
w=5
w=7
DC
2.30%±0.45
6.56%±0.72
7.81%±0.74
8.98%±0.75
8.90%±0.73
8.79%±0.71
8.58%±0.69
ICF Top
0.00%±0.00
5.12%±0.67
8.17%±0.81
10.06%±0.88
3.85%±0.54
1.20%±0.29
0.00%±0.00
Appendix
Table 7: Ablation on the guidance scale w . Values are mean percentage improvement (%) over the baseline design ± std over 5 runs.
Selection rule
w=1
w=2
w=3
w=4
Full selection rule
8.27%
11.20%
4.14%
3.59%
Geometric-only rule
6.14%
9.44%
4.01%
3.15%
Appendix
Table 8: Surrogate-only selection of the guidance scale w on 100 held-out ICF Top samples. Values are the mean surrogate-predicted yield gain (%) of the candidate selected per sample; no oracle evaluation is used. Bold : best per row.
Task
J=10
J=20
J=30
J=40
J=50
J=75
J=100
DC
7.90%±0.71
8.66%±0.72
8.92%±0.69
8.98%±0.75
8.97%±0.81
8.97%±0.73
8.94%±0.73
ICF Top
0.56%±0.18
1.64%±0.31
3.46%±0.49
5.38%±0.62
6.82%±0.74
8.94%±0.85
10.06%±0.88
Appendix
Table 9: Ablation on the number of optimization steps J . Values are mean percentage improvement (%) over the baseline design ± std over 5 runs.
Task
η=10−1
η=5×10−2
η=2×10−2
η=10−2
η=10−3
DC
8.22%±0.72
8.85%±0.74
8.98%±0.75
8.72%±0.74
7.66%±0.70
ICF Top
2.34%±0.42
5.33%±0.65
9.07%±0.85
9.05%±0.85
10.06%±0.88
Appendix
Table 10: Ablation on the optimization learning rate η . Values are mean percentage improvement (%) over the baseline design ± std over 5 runs.
Task
T=10
T=25
T=50
DC
8.84%±0.73
8.98%±0.75
8.97%±0.74
ICF Top
9.90%±0.86
10.06%±0.88
10.05%±0.87
Appendix
Table 11: Ablation on the number of DDIM inference steps T . Values are mean percentage improvement (%) over the baseline design ± std over 5 runs.
Task
All
Number of optimizable inputs
DC
8.98%±0.75
5.14%±0.61 ( do=1 )
5.67%±0.64 ( do=2 )
5.89%±0.65 ( do=4 )
7.97%±0.72 ( do=6 )
ICF
10.06%±0.88
4.02%±0.56 ( do=1 )
7.97%±0.79 ( do=4 )
8.74%±0.83 ( do=9 )
8.97%±0.85 ( do=15 )
Appendix
Table 12: Ablation on the number of optimizable conditioning inputs do . Values are mean percentage improvement (%) over the baseline design ± std over 5 runs.
Optimized variable
ICF Top
DC
Latent noise xT
7.56%±0.76
3.62%±0.26
Conditioning copt (D2C)
10.06%±0.88
8.98%±0.75
Appendix
Table 13: Conditioning optimization versus latent-noise optimization on the real-world tasks. Values are mean percentage improvement (%) over the baseline design ± std over 5 runs. Bold : best.
Method
ICF Standard
ICF Top
DC
BDI
27.40±1.28
18.24±1.11
6.00±0.24
Brute Force
32.97±1.36
31.26±1.41
64.50±2.58
CbAS
31.84±1.17
18.52±0.83
39.23±1.61
D2C (Ours)
81.23±2.86
75.12±2.78
100.00±0
CMA-ES
29.97±1.19
19.59±0.97
42.21±1.59
COMs
25.82±0.97
9.12±0.24
40.13±1.80
Appendix
Table 14: Constraint-satisfying improvement rate (%) on the real-world tasks. Values are mean constraint-satisfying improvement rate ± std over 5 runs, where the metric is the percentage of evaluation samples for which the final selected design achieves nonzero gain relative to the baseline (equivalently, at least one valid improving candidate is found). Higher is better.
Task
1×3
5×3
10×3
20×1
20×2
20×3
20×5
ICF Top
0.86%±0.24
4.59%±0.58
6.50%±0.72
5.72%±0.69
8.99%±0.85
9.64%±0.86
10.06%±0.88
DC
4.21%±0.57
7.82%±0.74
8.66%±0.69
8.41%±0.64
8.83%±0.72
8.91%±0.74
8.98%±0.75
Appendix
Table 15: Ablation on the candidate budget Nz×Nλ . Values are mean ± standard deviation over 5 seeds. Configurations are labeled by their Nz×Nλ values.
Method
ICF Top
DC
BDI
2.5
2.9
Brute Force
23.2
35.7
CbAS
14.2
17.5
CMA-ES
35.6
43.7
COMs
18.3
32.9
DDOM
2.3
3.6
Appendix
Table 16: Computation time (seconds per sample) for each method. Lower is better.
College of Computer Science and Technology, National University of Defense Technology, Changsha 410073, China · Bioinformatics Center of AMMS, Beijing 100080, China