Christopher Beckham

Robust Guided Diffusion for Offline Black-Box Optimization

Can Chen

Zixuan Liu

Xue (Steve) Liu

Offline black-box optimization aims to maximize a black-box function using an offline dataset of designs and their measured properties. Two … (see more)main approaches have emerged: the forward approach, which learns a mapping from input to its value, thereby acting as a proxy to guide optimization, and the inverse approach, which learns a mapping from value to input for conditional generation. (a) Although proxy-free~(classifier-free) diffusion shows promise in robustly modeling the inverse mapping, it lacks explicit guidance from proxies, essential for generating high-performance samples beyond the training distribution. Therefore, we propose \textit{proxy-enhanced sampling} which utilizes the explicit guidance from a trained proxy to bolster proxy-free diffusion with enhanced sampling control. (b) Yet, the trained proxy is susceptible to out-of-distribution issues. To address this, we devise the module \textit{diffusion-based proxy refinement}, which seamlessly integrates insights from proxy-free diffusion back into the proxy for refinement. To sum up, we propose \textit{\textbf{R}obust \textbf{G}uided \textbf{D}iffusion for Offline Black-box Optimization}~(\textbf{RGD}), combining the advantages of proxy~(explicit guidance) and proxy-free diffusion~(robustness) for effective conditional generation. RGD achieves state-of-the-art results on various design-bench tasks, underscoring its efficacy. Our code is at https://github.com/GGchen1997/RGD.

2024-10-01

ArXiv (preprint)

Exploring validation metrics for offline model-based optimisation with diffusion models

Alexandre Piché

David Vazquez

2024-06-13

TMLR (accepted)

Exploring validation metrics for ofﬂine model-based optimisation

Alexandre Piché

David Vazquez

In ofﬂine model-based optimisation (MBO) we are interested in using machine learning to de-sign candidates that maximise some measure of d… (see more)esirability through an expensive but real-world scoring process. Ofﬂine MBO tries to approximate this expensive scoring function and use that to evaluate generated designs, however evaluation is non-exact because one approximation is being evaluated with another. Instead, we ask ourselves: if we did have the real world scoring function at hand, what cheap-to-compute validation metrics would correlate best with this? Since the real-world scoring function is available for simulated MBO datasets, insights obtained from this can be transferred over to real-world ofﬂine MBO tasks where the real-world scoring function is expensive to compute. To address this, we propose a conceptual evaluation framework that is amenable to measuring extrapolation, and apply this to conditional denoising diffusion models. Empirically, we ﬁnd that two validation metrics – agreement and Frechet distance – correlate quite well with the ground truth. When there is high variability in conditional generation, feedback is required in the form of an approximated version of the real-world scoring function. Furthermore, we ﬁnd that generating high-scoring samples may require heavily weighting the generative model in favour of sample quality, potentially at the cost of sample diversity.

2024-01-01

Trans. Mach. Learn. Res. (published)

dblp.uni-trier.de

Parallel-mentoring for Offline Model-based Optimization

Can Chen

Zixuan Liu

Parallel-mentoring for Offline Model-based Optimization

Can Chen

Zixuan Liu

Xue (Steve) Liu

We study offline model-based optimization to maximize a black-box objective function with a static dataset of designs and scores. These desi… (see more)gns encompass a variety of domains, including materials, robots, DNA sequences, and proteins. A common approach trains a proxy on the static dataset and performs gradient ascent to obtain new designs. However, this often results in poor designs due to the proxy inaccuracies for out-of-distribution designs. Recent studies indicate that (a) gradient ascent with a mean ensemble of proxies generally outperforms simple gradient ascent, and (b) a trained proxy provides weak ranking supervision signals for design selection. Motivated by (a) and (b), we propose

2023-09-21

NeurIPS.cc/2023/Conference (poster)

Conservative objective models are a special kind of contrastive divergence-based energy model

In this work we theoretically show that conservative objective models (COMs) for offline model-based optimisation (MBO) are a special kind o… (see more)f contrastive divergence-based energy model, one where the energy function represents both the unconditional probability of the input and the conditional probability of the reward variable. While the initial formulation only samples modes from its learned distribution, we propose a simple fix that replaces its gradient ascent sampler with a Langevin MCMC sampler. This gives rise to a special probabilistic model where the probability of sampling an input is proportional to its predicted reward. Lastly, we show that better samples can be obtained if the model is decoupled so that the unconditional and conditional probabilities are modelled separately.

2023-04-07

ArXiv (preprint)

Visual Question Answering From Another Perspective: CLEVR Mental Rotation Tests

2023-04-01

Pattern Recognition (published)

Score-based Diffusion Models in Function Space

Jae Hyun Lim

Nikola B. Kovachki

R. Baptista

Kamyar Azizzadenesheli

Jean Kossaifi

Vikram Voleti

Jiaming Song

Karsten Kreis

Jan Kautz

Arash Vahdat

Animashree Anandkumar

2023-02-14

ArXiv (preprint)

Challenges in leveraging GANs for few-shot data augmentation

Issam Hadj Laradji

Pau Rodriguez

David Vazquez

Derek Nowrouzezahrai

2022-01-01

arXiv.org (preprint)

Overcoming challenges in leveraging GANs for few-shot data augmentation

Issam Hadj Laradji

Pau Rodriguez

David Vazquez

Derek Nowrouzezahrai

2022-01-01

CoLLAs (published)

proceedings.mlr.press

Towards good validation metrics for generative models in offline model-based optimisation

Alexandre Piché

David Vazquez

In this work we propose a principled evaluation framework for model-based optimisation to measure how well a generative model can extrapolat… (see more)e. We achieve this by interpreting the training and validation splits as draws from their respective ‘truncated’ ground truth distributions, where examples in the validation set contain scores much larger than those in the training set. Model selection is performed on the validation set for some prescribed validation metric. A major research question however is in determining what validation metric correlates best with the expected value of generated candidates with respect to the ground truth oracle; work towards answering this question can translate to large economic gains since it is expensive to evaluate the ground truth oracle in the real world. We compare various validation metrics for generative adversarial networks using our framework. We also discuss limitations with our framework with respect to existing datasets and how progress can be made to mitigate them. 1

2022-01-01

arXiv.org (preprint)