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 Uncertainty


Refined climatologies of future precipitation over High Mountain Asia using probabilistic ensemble learning

arXiv.org Machine Learning

High Mountain Asia holds the largest concentration of frozen water outside the polar regions, serving as a crucial water source for more than 1.9 billion people. In the face of climate change, precipitation represents the largest source of uncertainty for hydrological modelling in this area. Future precipitation predictions remain challenging due to complex orography, lack of in situ hydrological observations, and limitations in climate model resolution and parametrisation for this region. To address the uncertainty posed by these challenges, climate models are often aggregated into multi-model ensembles. While multi-model ensembles are known to improve the predictive accuracy and analysis of future climate projections, consensus regarding how models are aggregated is lacking. In this study, we propose a probabilistic machine learning framework to systematically combine 13 regional climate models from the Coordinated Regional Downscaling Experiment (CORDEX) over High Mountain Asia. Our approach accounts for seasonal and spatial biases within the models, enabling the prediction of more faithful precipitation distributions. The framework is validated against gridded historical precipitation data and is used to generate projections for the near-future (2036-2065) and far-future (2066-2095) under RCP4.5 and RCP8.5 scenarios.


I-trustworthy Models. A framework for trustworthiness evaluation of probabilistic classifiers

arXiv.org Machine Learning

As probabilistic models continue to permeate various facets of our society and contribute to scientific advancements, it becomes a necessity to go beyond traditional metrics such as predictive accuracy and error rates and assess their trustworthiness. Grounded in the competence-based theory of trust, this work formalizes I-trustworthy framework -- a novel framework for assessing the trustworthiness of probabilistic classifiers for inference tasks by linking local calibration to trustworthiness. To assess I-trustworthiness, we use the local calibration error (LCE) and develop a method of hypothesis-testing. This method utilizes a kernel-based test statistic, Kernel Local Calibration Error (KLCE), to test local calibration of a probabilistic classifier. This study provides theoretical guarantees by offering convergence bounds for an unbiased estimator of KLCE. Additionally, we present a diagnostic tool designed to identify and measure biases in cases of miscalibration. The effectiveness of the proposed test statistic is demonstrated through its application to both simulated and real-world datasets. Finally, LCE of related recalibration methods is studied, and we provide evidence of insufficiency of existing methods to achieve I-trustworthiness.


Review for NeurIPS paper: Gibbs Sampling with People

Neural Information Processing Systems

Weaknesses: Overall, I thought this was a strong paper. The main concerns I had were as follows: (1) Mode-seeking versus showing the distribution: The aggregated results in the first experiment seem to show much more homogeneity than the results for GSP or MCMCP. It seems like one limitation of this approach might be that there is limited exploration of the space, perhaps making it hard to move between modes, and also makes it more difficult to see the full shape of the distribution, which I have often taken to be a goal in work using MCMCP. The movement between optimization and seeking a distribution is discussed to some extent in the paper, but I would be interested in seeing this discussed more (and perhaps whether GP without aggregation is likely to lead to more optimization than MCMCP). In the author response, they have shown additional information suggesting that GSP is more mode-seeking but also does a better job of capturing the distribution.


Review for NeurIPS paper: Gibbs Sampling with People

Neural Information Processing Systems

This paper introduces a new method for eliciting human representations of perceptual concepts, such as what RGB values people think correspond to the color "sunset" or what auditory dimensions (e.g. Rather than eliciting representations via guess-and-check (i.e., start with a dataset and then apply human-generated labels), this method (Gibbs Sampling with People, or GSP) enables inference to go in the other direction (i.e., start with labels, and then identify percepts that match those labels). GSP extends prior work (MCMC with People) to allow eliciting representations of much higher-dimensional stimuli. The reviewers unanimously praised this paper for tackling an important and relevant problem in cognitive science, for its breadth of empirical results, and for its novelty over prior work. R2 stated that the paper is "impressive in scale, scope, and results", R3 stated that it was "very relevant to the NeurIPS community and very novel", and R4 felt there could be "a potentially large impact of this work" with "substantial interest" amongst the NeurIPS community.


Reviews: Adaptive Density Estimation for Generative Models

Neural Information Processing Systems

Summary: The authors propose a hybrid method that combines VAEs with adversarial training and flow based models. In particular, they derive an explicit density function p(x) where the likelihood can be evaluated, the corresponding components p(x z) are more flexible than the standard VAE that utilizes diagonal Gaussians, and the generated samples have better quality than a standard VAE. The basic idea of the proposed model is that the VAE is defined between a latent space and an intermediate representation space, and then, the representation space is connected with the data space through an invertible non-linear flow. In general, I think the paper is quite well written, but on the same time I believe that there is a lot of compressed information, and the consequence is that in some parts it is not even clear what the authors want to say (see Clarity comments). The proposed idea of the paper seems quite interesting, but on the same time I have some doubts (see Quality comments).


Reviews: Adaptive Density Estimation for Generative Models

Neural Information Processing Systems

This paper proposes a new hybrid generative model, combining a maximum-likelihood approach with GANs. The authors are to be commended for their practical and conceptually interesting work. In the final version, the paper would also benefit from a discussion of [1], related work that introduces an alternative maximum likelihood perspective of GANs, and provides Bayesian generalizations.


Scalable Quasi-Bayesian Inference for Instrumental Variable Regression

Neural Information Processing Systems

Recent years have witnessed an upsurge of interest in employing flexible machine learning models for instrumental variable (IV) regression, but the development of uncertainty quantification methodology is still lacking. In this work we present a scalable quasi-Bayesian procedure for IV regression, building upon the recently developed kernelized IV models. Contrary to Bayesian modeling for IV, our approach does not require additional assumptions on the data generating process, and leads to a scalable approximate inference algorithm with time cost comparable to the corresponding point estimation methods. Our algorithm can be further extended to work with neural network models. We analyze the theoretical properties of the proposed quasi-posterior, and demonstrate through empirical evaluation the competitive performance of our method.


Review for NeurIPS paper: Hamiltonian Monte Carlo using an adjoint-differentiated Laplace approximation: Bayesian inference for latent Gaussian models and beyond

Neural Information Processing Systems

Weaknesses: My main questions regarding the paper: 1) When computing the Laplace approximation, this still requires calculation of the Hessian, which I believe is with respect to the latent (theta). This is referred to as W in Algorithm 1. Would it be possible to comment further on the kind of trade-off between implementing full-HMC, versus the overhead of calculating the Hessian. I think this is the issue you are referring to in the second paragraph of the discussion section, whereby you mention higher-order automatic differentiation. I assume you stick to analytical Hessians (e.g. For example "Semi-Separable Hamiltonian Monte Carlo for Inference in Bayesian Hierarchical Models" by Zhang and Sutton jointly sample over hyperparameters and parameters to overcome similar funnel-like behaviours to that of the Gaussian latent variable models that you explore.


Reviews: Dichotomize and Generalize: PAC-Bayesian Binary Activated Deep Neural Networks

Neural Information Processing Systems

One contribution is a new approach for training neural networks with binary activations. The second contribution is PAC-Bayesian generalization bounds for binary activated neural networks that, when used as the training objective, come very close to test accuracy (i.e. The gap between the training and test performance is also much smaller. I think this is very promising for training more robust networks. The method actually recovers variational Bayesian learning when the coefficient C is fixed, but in contrast to it, this coefficient is learned in a principled way.


A New Approach for Knowledge Generation Using Active Inference

arXiv.org Artificial Intelligence

There are various models proposed on how knowledge is generated in the human brain including the semantic networks model. Although this model has been widely studied and even computational models are presented, but, due to various limits and inefficiencies in the generation of different types of knowledge, its application is limited to semantic knowledge because of has been formed according to semantic memory and declarative knowledge and has many limits in explaining various procedural and conditional knowledge. Given the importance of providing an appropriate model for knowledge generation, especially in the areas of improving human cognitive functions or building intelligent machines, improving existing models in knowledge generation or providing more comprehensive models is of great importance. In the current study, based on the free energy principle of the brain, is the researchers proposed a model for generating three types of declarative, procedural, and conditional knowledge. While explaining different types of knowledge, this model is capable to compute and generate concepts from stimuli based on probabilistic mathematics and the action-perception process (active inference). The proposed model is unsupervised learning that can update itself using a combination of different stimuli as a generative model can generate new concepts of unsupervised received stimuli. In this model, the active inference process is used in the generation of procedural and conditional knowledge and the perception process is used to generate declarative knowledge.