Learning Graphical Models
Towards Automated Causal Discovery: a case study on 5G telecommunication data
Biza, Konstantina, Ntroumpogiannis, Antonios, Triantafillou, Sofia, Tsamardinos, Ioannis
Causal Discovery is a field of machine learning and statistics aiming to induce causal knowledge from data [29, 47]. There is a large corpus of algorithms and methodologies in the field, spanning tasks like learning causal models, estimating causal effects, and determining optimal interventions. While there are several public libraries of algorithms for these tasks, combining the algorithms and applying them to any given problem is a challenging endeavor that requires extensive knowledge of the methods and a deep understanding of the theory to interpret results. In this paper, we introduce the concept of Automated Causal Discovery (AutoCD) (not to be confused with Automated Causal Inference [14, 26]; see Section 3), defined as the effort to fully automate the application of causal discovery and causal reasoning. AutoCD's goals should be to deliver not just the optimal causal model that fits the data, but all information, answers to queries, visualizations, interpretations, and explanations that a human expert analyst would.
Framing in the Presence of Supporting Data: A Case Study in U.S. Economic News
Leto, Alexandria, Pickens, Elliot, Needell, Coen D., Rothschild, David, Pacheco, Maria Leonor
The mainstream media has much leeway in what it chooses to cover and how it covers it. These choices have real-world consequences on what people know and their subsequent behaviors. However, the lack of objective measures to evaluate editorial choices makes research in this area particularly difficult. In this paper, we argue that there are newsworthy topics where objective measures exist in the form of supporting data and propose a computational framework to analyze editorial choices in this setup. We focus on the economy because the reporting of economic indicators presents us with a relatively easy way to determine both the selection and framing of various publications. Their values provide a ground truth of how the economy is doing relative to how the publications choose to cover it. To do this, we define frame prediction as a set of interdependent tasks. At the article level, we learn to identify the reported stance towards the general state of the economy. Then, for every numerical quantity reported in the article, we learn to identify whether it corresponds to an economic indicator and whether it is being reported in a positive or negative way. To perform our analysis, we track six American publishers and each article that appeared in the top 10 slots of their landing page between 2015 and 2023.
SHM-Traffic: DRL and Transfer learning based UAV Control for Structural Health Monitoring of Bridges with Traffic
Gadiraju, Divija Swetha, Azam, Saeed Eftekhar, Khazanchi, Deepak
This work focuses on using advanced techniques for structural health monitoring (SHM) for bridges with Traffic. We propose an approach using deep reinforcement learning (DRL)-based control for Unmanned Aerial Vehicle (UAV). Our approach conducts a concrete bridge deck survey while traffic is ongoing and detects cracks. The UAV performs the crack detection, and the location of cracks is initially unknown. We use two edge detection techniques. First, we use canny edge detection for crack detection. We also use a Convolutional Neural Network (CNN) for crack detection and compare it with canny edge detection. Transfer learning is applied using CNN with pre-trained weights obtained from a crack image dataset. This enables the model to adapt and improve its performance in identifying and localizing cracks. Proximal Policy Optimization (PPO) is applied for UAV control and bridge surveys. The experimentation across various scenarios is performed to evaluate the performance of the proposed methodology. Key metrics such as task completion time and reward convergence are observed to gauge the effectiveness of the approach. We observe that the Canny edge detector offers up to 40\% lower task completion time, while the CNN excels in up to 12\% better damage detection and 1.8 times better rewards.
Stacking Factorizing Partitioned Expressions in Hybrid Bayesian Network Models
Lin, Peng, Neil, Martin, Fenton, Norman
Hybrid Bayesian networks (HBN) contain complex conditional probabilistic distributions (CPD) specified as partitioned expressions over discrete and continuous variables. The size of these CPDs grows exponentially with the number of parent nodes when using discrete inference, resulting in significant inefficiency. Normally, an effective way to reduce the CPD size is to use a binary factorization (BF) algorithm to decompose the statistical or arithmetic functions in the CPD by factorizing the number of connected parent nodes to sets of size two. However, the BF algorithm was not designed to handle partitioned expressions. Hence, we propose a new algorithm called stacking factorization (SF) to decompose the partitioned expressions. The SF algorithm creates intermediate nodes to incrementally reconstruct the densities in the original partitioned expression, allowing no more than two continuous parent nodes to be connected to each child node in the resulting HBN. SF can be either used independently or combined with the BF algorithm. We show that the SF+BF algorithm significantly reduces the CPD size and contributes to lowering the tree-width of a model, thus improving efficiency.
Large-Scale Actionless Video Pre-Training via Discrete Diffusion for Efficient Policy Learning
He, Haoran, Bai, Chenjia, Pan, Ling, Zhang, Weinan, Zhao, Bin, Li, Xuelong
Learning a generalist embodied agent capable of completing multiple tasks poses challenges, primarily stemming from the scarcity of action-labeled robotic datasets. In contrast, a vast amount of human videos exist, capturing intricate tasks and interactions with the physical world. Promising prospects arise for utilizing actionless human videos for pre-training and transferring the knowledge to facilitate robot policy learning through limited robot demonstrations. In this paper, we introduce a novel framework that leverages a unified discrete diffusion to combine generative pre-training on human videos and policy fine-tuning on a small number of action-labeled robot videos. We start by compressing both human and robot videos into unified video tokens. In the pre-training stage, we employ a discrete diffusion model with a mask-and-replace diffusion strategy to predict future video tokens in the latent space. In the fine-tuning stage, we harness the imagined future videos to guide low-level action learning trained on a limited set of robot data. Experiments demonstrate that our method generates high-fidelity future videos for planning and enhances the fine-tuned policies compared to previous state-of-the-art approaches with superior generalization ability. Our project website is available at https://video-diff.github.io/.
Kinematically Constrained Human-like Bimanual Robot-to-Human Handovers
Göksu, Yasemin, Correia, Antonio De Almeida, Prasad, Vignesh, Kshirsagar, Alap, Koert, Dorothea, Peters, Jan, Chalvatzaki, Georgia
Bimanual handovers are crucial for transferring large, deformable or delicate objects. This paper proposes a framework for generating kinematically constrained human-like bimanual robot motions to ensure seamless and natural robot-to-human object handovers. We use a Hidden Semi-Markov Model (HSMM) to reactively generate suitable response trajectories for a robot based on the observed human partner's motion. The trajectories are adapted with task space constraints to ensure accurate handovers. Results from a pilot study show that our approach is perceived as more human--like compared to a baseline Inverse Kinematics approach.
Nonlinear Bayesian optimal experimental design using logarithmic Sobolev inequalities
Li, Fengyi, Belhadji, Ayoub, Marzouk, Youssef
The optimal experimental design (OED) problem arises in numerous settings, with applications ranging from combustion kinetics Huan & Marzouk (2013), sensor placement for weather prediction Krause et al. (2008), containment source identification Attia et al. (2018), to pharmaceutical trials Djuris et al. (2024). A commonly addressed version of the OED problem centers on the fundamental question of selecting an optimal subset of k observations from a total pool of n possible candidates, with the goal of learning the parameters of a statistical model for the observations. In the Bayesian framework, these parameters are endowed with a prior distribution to represent our state of knowledge before seeing the data. A posterior distribution on the parameters is obtained by conditioning on the observations. A commonly used experimental design criterion is then the mutual information (MI) between the parameters and the selected observations or, equivalently, the expected information gain from prior to posterior, which should be maximized.
On the Curses of Future and History in Future-dependent Value Functions for Off-policy Evaluation
We study off-policy evaluation (OPE) in partially observable environments with complex observations, with the goal of developing estimators whose guarantee avoids exponential dependence on the horizon. While such estimators exist for MDPs and POMDPs can be converted to history-based MDPs, their estimation errors depend on the state-density ratio for MDPs which becomes history ratios after conversion, an exponential object. Recently, Uehara et al. (2022) proposed future-dependent value functions as a promising framework to address this issue, where the guarantee for memoryless policies depends on the density ratio over the latent state space. However, it also depends on the boundedness of the future-dependent value function and other related quantities, which we show could be exponential-in-length and thus erasing the advantage of the method. In this paper, we discover novel coverage assumptions tailored to the structure of POMDPs, such as outcome coverage and belief coverage. These assumptions not only enable polynomial bounds on the aforementioned quantities, but also lead to the discovery of new algorithms with complementary properties.
Rao-Blackwellising Bayesian Causal Inference
Toth, Christian, Knoll, Christian, Pernkopf, Franz, Peharz, Robert
Bayesian causal inference, i.e., inferring a posterior over causal models for the use in downstream causal reasoning tasks, poses a hard computational inference problem that is little explored in literature. In this work, we combine techniques from order-based MCMC structure learning with recent advances in gradient-based graph learning into an effective Bayesian causal inference framework. Specifically, we decompose the problem of inferring the causal structure into (i) inferring a topological order over variables and (ii) inferring the parent sets for each variable. When limiting the number of parents per variable, we can exactly marginalise over the parent sets in polynomial time. We further use Gaussian processes to model the unknown causal mechanisms, which also allows their exact marginalisation. This introduces a Rao-Blackwellization scheme, where all components are eliminated from the model, except for the causal order, for which we learn a distribution via gradient-based optimisation. The combination of Rao-Blackwellization with our sequential inference procedure for causal orders yields state-of-the-art on linear and non-linear additive noise benchmarks with scale-free and Erdos-Renyi graph structures.
How Transformers Learn Causal Structure with Gradient Descent
Nichani, Eshaan, Damian, Alex, Lee, Jason D.
The incredible success of transformers on sequence modeling tasks can be largely attributed to the self-attention mechanism, which allows information to be transferred between different parts of a sequence. Self-attention allows transformers to encode causal structure which makes them particularly suitable for sequence modeling. However, the process by which transformers learn such causal structure via gradient-based training algorithms remains poorly understood. To better understand this process, we introduce an in-context learning task that requires learning latent causal structure. We prove that gradient descent on a simplified two-layer transformer learns to solve this task by encoding the latent causal graph in the first attention layer. The key insight of our proof is that the gradient of the attention matrix encodes the mutual information between tokens. As a consequence of the data processing inequality, the largest entries of this gradient correspond to edges in the latent causal graph. As a special case, when the sequences are generated from in-context Markov chains, we prove that transformers learn an induction head (Olsson et al., 2022). We confirm our theoretical findings by showing that transformers trained on our in-context learning task are able to recover a wide variety of causal structures.