近几十年来，技术进步使得可以收集大数据集。在这种情况下，基于模型的群集是一种非常流行的，灵活和可解释的方法，用于在明确定义的统计框架中进行数据探索。大型数据集的增加之一是缺失值更频繁。但是，传统方式（由于丢弃具有缺失的值或估算方法的观察）不是为聚类目的而设计的。此外，它们很少适用于常规情况，虽然在实践中频繁地缺失，但是当缺失取决于未观察到的数据值时，缺失就缺失（mnar）值，而且可能在观察到的数据值上。本文的目标是通过直接在基于模型的聚类算法内嵌入MNAR数据来提出一种新的方法。我们为数据和缺失数据指示器的联合分布进行了选择模型。它对应于数据分布的混合模型和缺失数据机制的一般Mnar模型，其可以取决于底层类（未知）和/或缺失变量本身的值。导出大量有意义的MNAR子模型，对每个子模型研究了参数的可识别性，这通常是任何MNAR提案的关键问题。考虑EM和随机EM算法估计。最后，我们对合成数据的提议子模型进行了实证评估，我们说明了我们的方法对医疗寄存器的方法，创伤者（R）数据集。

Gradient boosting is a prediction method that iteratively combines weak learners to produce a complex and accurate model. From an optimization point of view, the learning procedure of gradient boosting mimics a gradient descent on a functional variable. This paper proposes to build upon the proximal point algorithm, when the empirical risk to minimize is not differentiable, in order to introduce a novel boosting approach, called proximal boosting. It comes with a companion algorithm inspired by [1] and called residual proximal boosting, which is aimed at better controlling the approximation error. Theoretical convergence is proved for these two procedures under different hypotheses on the empirical risk and advantages of leveraging proximal methods for boosting are illustrated by numerical experiments on simulated and real-world data. In particular, we exhibit a favorable comparison over gradient boosting regarding convergence rate and prediction accuracy.

We study the problem of planning under model uncertainty in an online meta-reinforcement learning (RL) setting where an agent is presented with a sequence of related tasks with limited interactions per task. The agent can use its experience in each task and across tasks to estimate both the transition model and the distribution over tasks. We propose an algorithm to meta-learn the underlying structure across tasks, utilize it to plan in each task, and upper-bound the regret of the planning loss. Our bound suggests that the average regret over tasks decreases as the number of tasks increases and as the tasks are more similar. In the classical single-task setting, it is known that the planning horizon should depend on the estimated model's accuracy, that is, on the number of samples within task. We generalize this finding to meta-RL and study this dependence of planning horizons on the number of tasks. Based on our theoretical findings, we derive heuristics for selecting slowly increasing discount factors, and we validate its significance empirically.

Underwater images are altered by the physical characteristics of the medium through which light rays pass before reaching the optical sensor. Scattering and strong wavelength-dependent absorption significantly modify the captured colors depending on the distance of observed elements to the image plane. In this paper, we aim to recover the original colors of the scene as if the water had no effect on them. We propose two novel methods that rely on different sets of inputs. The first assumes that pixel intensities in the restored image are normally distributed within each color channel, leading to an alternative optimization of the well-known \textit{Sea-thru} method which acts on single images and their distance maps. We additionally introduce SUCRe, a new method that further exploits the scene's 3D Structure for Underwater Color Restoration. By following points in multiple images and tracking their intensities at different distances to the sensor we constrain the optimization of the image formation model parameters. When compared to similar existing approaches, SUCRe provides clear improvements in a variety of scenarios ranging from natural light to deep-sea environments. The code for both approaches is publicly available at https://github.com/clementinboittiaux/sucre .

We study representation learning for efficient imitation learning over linear systems. In particular, we consider a setting where learning is split into two phases: (a) a pre-training step where a shared $k$-dimensional representation is learned from $H$ source policies, and (b) a target policy fine-tuning step where the learned representation is used to parameterize the policy class. We find that the imitation gap over trajectories generated by the learned target policy is bounded by $\tilde{O}\left( \frac{k n_x}{HN_{\mathrm{shared}}} + \frac{k n_u}{N_{\mathrm{target}}}\right)$, where $n_x > k$ is the state dimension, $n_u$ is the input dimension, $N_{\mathrm{shared}}$ denotes the total amount of data collected for each policy during representation learning, and $N_{\mathrm{target}}$ is the amount of target task data. This result formalizes the intuition that aggregating data across related tasks to learn a representation can significantly improve the sample efficiency of learning a target task. The trends suggested by this bound are corroborated in simulation.

Forecasting the state of vegetation in response to climate and weather events is a major challenge. Its implementation will prove crucial in predicting crop yield, forest damage, or more generally the impact on ecosystems services relevant for socio-economic functioning, which if absent can lead to humanitarian disasters. Vegetation status depends on weather and environmental conditions that modulate complex ecological processes taking place at several timescales. Interactions between vegetation and different environmental drivers express responses at instantaneous but also time-lagged effects, often showing an emerging spatial context at landscape and regional scales. We formulate the land surface forecasting task as a strongly guided video prediction task where the objective is to forecast the vegetation developing at very fine resolution using topography and weather variables to guide the prediction. We use a Convolutional LSTM (ConvLSTM) architecture to address this task and predict changes in the vegetation state in Africa using Sentinel-2 satellite NDVI, having ERA5 weather reanalysis, SMAP satellite measurements, and topography (DEM of SRTMv4.1) as variables to guide the prediction. Ours results highlight how ConvLSTM models can not only forecast the seasonal evolution of NDVI at high resolution, but also the differential impacts of weather anomalies over the baselines. The model is able to predict different vegetation types, even those with very high NDVI variability during target length, which is promising to support anticipatory actions in the context of drought-related disasters.

Partially observable Markov decision processes (POMDPs) provide a flexible representation for real-world decision and control problems. However, POMDPs are notoriously difficult to solve, especially when the state and observation spaces are continuous or hybrid, which is often the case for physical systems. While recent online sampling-based POMDP algorithms that plan with observation likelihood weighting have shown practical effectiveness, a general theory characterizing the approximation error of the particle filtering techniques that these algorithms use has not previously been proposed. Our main contribution is bounding the error between any POMDP and its corresponding finite sample particle belief MDP (PB-MDP) approximation. This fundamental bridge between PB-MDPs and POMDPs allows us to adapt any sampling-based MDP algorithm to a POMDP by solving the corresponding particle belief MDP, thereby extending the convergence guarantees of the MDP algorithm to the POMDP. Practically, this is implemented by using the particle filter belief transition model as the generative model for the MDP solver. While this requires access to the observation density model from the POMDP, it only increases the transition sampling complexity of the MDP solver by a factor of $\mathcal{O}(C)$, where $C$ is the number of particles. Thus, when combined with sparse sampling MDP algorithms, this approach can yield algorithms for POMDPs that have no direct theoretical dependence on the size of the state and observation spaces. In addition to our theoretical contribution, we perform five numerical experiments on benchmark POMDPs to demonstrate that a simple MDP algorithm adapted using PB-MDP approximation, Sparse-PFT, achieves performance competitive with other leading continuous observation POMDP solvers.

地震数据中的噪声来自许多来源，并且正在不断发展。使用监督的深度学习程序来降级地震数据集通常会导致性能差：这是由于缺乏无噪声的现场数据来充当训练目标以及合成数据集和现场数据集之间特性的巨大差异。自我监督，盲点网络通常通过直接在原始嘈杂的数据上训练来克服这些限制。但是，这样的网络通常依赖于随机噪声假设，并且在存在最小相关的噪声的情况下，它们的降解能力迅速降低。从盲点延伸到盲面可以有效地沿特定方向抑制连贯的噪声，但不能适应噪声的不断变化的特性。为了抢占网络预测信号并减少其学习噪声属性的机会的能力，我们在以自欺欺人的方式进行微调的方式，在节俭生成的合成数据集上对网络进行初始监督的培训。感兴趣的数据集。考虑到峰值信噪比的变化以及观察到的噪声量减少和信号泄漏的体积，我们说明了从监督的基础训练中的权重来初始化自我监督网络的明显好处。通过在字段数据集上进行的测试进一步支持，在该数据集中进行了微调网络在信号保存和降低噪声之间达到最佳平衡。最后，使用不切实际的，节俭生成的合成数据集用于监督的基础培训包括许多好处：需要最少的先验地质知识，大大降低了数据集生成的计算成本，并减少了重新训练的要求。网络应记录条件更改，仅举几例。

我们研究Claire（一种差异性多形状，多-GPU图像注册算法和软件）的性能 - 在具有数十亿素素的大规模生物医学成像应用中。在这样的分辨率下，大多数用于差异图像注册的软件包非常昂贵。结果，从业人员首先要大量删除原始图像，然后使用现有工具进行注册。我们的主要贡献是对降采样对注册性能的影响的广泛分析。我们通过将用Claire获得的全分辨率注册与合成和现实成像数据集的低分辨率注册进行比较，研究了这种影响。我们的结果表明，完全分辨率的注册可以产生卓越的注册质量 - 但并非总是如此。例如，将合成图像从$ 1024^3 $减少到$ 256^3 $将骰子系数从92％降低到79％。但是，对于嘈杂或低对比度的高分辨率图像，差异不太明显。克莱尔不仅允许我们在几秒钟内注册临床相关大小的图像，而且还可以在合理的时间内以前所未有的分辨率注册图像。考虑的最高分辨率是$ 2816 \ times3016 \ times1162 $的清晰图像。据我们所知，这是有关此类决议中图像注册质量的首次研究。

文档级信息提取（IE）任务最近开始使用端到端的神经网络技术对其句子级别的IE同行进行认真重新审视。但是，对方法的评估在许多维度上受到限制。特别是，Precision/Recell/F1分数通常报道，几乎没有关于模型造成的错误范围的见解。我们基于Kummerfeld和Klein（2013）的工作，为基于转换的框架提出了用于文档级事件和（N- ARY）关系提取的自动化错误分析的框架。我们采用我们的框架来比较来自三个域的数据集上的两种最先进的文档级模板填充方法；然后，为了衡量IE自30年前成立以来的进展，与MUC-4（1992）评估的四个系统相比。