With the attention mechanism, transformers achieve significant empirical successes. Despite the intuitive understanding that transformers perform relational inference over long sequences to produce desirable representations, we lack a rigorous theory on how the attention mechanism achieves it. In particular, several intriguing questions remain open: (a) What makes a desirable representation? (b) How does the attention mechanism infer the desirable representation within the forward pass? (c) How does a pretraining procedure learn to infer the desirable representation through the backward pass? We observe that, as is the case in BERT and ViT, input tokens are often exchangeable since they already include positional encodings. The notion of exchangeability induces a latent variable model that is invariant to input sizes, which enables our theoretical analysis. - To answer (a) on representation, we establish the existence of a sufficient and minimal representation of input tokens. In particular, such a representation instantiates the posterior distribution of the latent variable given input tokens, which plays a central role in predicting output labels and solving downstream tasks. - To answer (b) on inference, we prove that attention with the desired parameter infers the latent posterior up to an approximation error, which is decreasing in input sizes. In detail, we quantify how attention approximates the conditional mean of the value given the key, which characterizes how it performs relational inference over long sequences. - To answer (c) on learning, we prove that both supervised and self-supervised objectives allow empirical risk minimization to learn the desired parameter up to a generalization error, which is independent of input sizes. Particularly, in the self-supervised setting, we identify a condition number that is pivotal to solving downstream tasks.

The ability to create realistic, animatable and relightable head avatars from casual video sequences would open up wide ranging applications in communication and entertainment. Current methods either build on explicit 3D morphable meshes (3DMM) or exploit neural implicit representations. The former are limited by fixed topology, while the latter are non-trivial to deform and inefficient to render. Furthermore, existing approaches entangle lighting in the color estimation, thus they are limited in re-rendering the avatar in new environments. In contrast, we propose PointAvatar, a deformable point-based representation that disentangles the source color into intrinsic albedo and normal-dependent shading. We demonstrate that PointAvatar bridges the gap between existing mesh- and implicit representations, combining high-quality geometry and appearance with topological flexibility, ease of deformation and rendering efficiency. We show that our method is able to generate animatable 3D avatars using monocular videos from multiple sources including hand-held smartphones, laptop webcams and internet videos, achieving state-of-the-art quality in challenging cases where previous methods fail, e.g., thin hair strands, while being significantly more efficient in training than competing methods.

The goal of multimodal abstractive summarization (MAS) is to produce a concise summary given the multimodal data (text and vision). Existing studies on MAS mainly focus on how to effectively use the extracted visual features, having achieved impressive success on the high-resource English dataset. However, less attention has been paid to the quality of the visual features to the summary, which may limit the model performance especially in the low- and zero-resource scenarios. In this paper, we propose to improve the summary quality through summary-oriented visual features. To this end, we devise two auxiliary tasks including \emph{vision to summary task} and \emph{masked image modeling task}. Together with the main summarization task, we optimize the MAS model via the training objectives of all these tasks. By these means, the MAS model can be enhanced by capturing the summary-oriented visual features, thereby yielding more accurate summaries. Experiments on 44 languages, covering mid-high-, low-, and zero-resource scenarios, verify the effectiveness and superiority of the proposed approach, which achieves state-of-the-art performance under all scenarios.

Neural Radiance Fields (NeRF) methods have proved effective as compact, high-quality and versatile representations for 3D scenes, and enable downstream tasks such as editing, retrieval, navigation, etc. Various neural architectures are vying for the core structure of NeRF, including the plain Multi-Layer Perceptron (MLP), sparse tensors, low-rank tensors, hashtables and their compositions. Each of these representations has its particular set of trade-offs. For example, the hashtable-based representations admit faster training and rendering but their lack of clear geometric meaning hampers downstream tasks like spatial-relation-aware editing. In this paper, we propose Progressive Volume Distillation (PVD), a systematic distillation method that allows any-to-any conversions between different architectures, including MLP, sparse or low-rank tensors, hashtables and their compositions. PVD consequently empowers downstream applications to optimally adapt the neural representations for the task at hand in a post hoc fashion. The conversions are fast, as distillation is progressively performed on different levels of volume representations, from shallower to deeper. We also employ special treatment of density to deal with its specific numerical instability problem. Empirical evidence is presented to validate our method on the NeRF-Synthetic, LLFF and TanksAndTemples datasets. For example, with PVD, an MLP-based NeRF model can be distilled from a hashtable-based Instant-NGP model at a 10X~20X faster speed than being trained the original NeRF from scratch, while achieving a superior level of synthesis quality. Code is available at https://github.com/megvii-research/AAAI2023-PVD.

Video super-resolution is one of the most popular tasks on mobile devices, being widely used for an automatic improvement of low-bitrate and low-resolution video streams. While numerous solutions have been proposed for this problem, they are usually quite computationally demanding, demonstrating low FPS rates and power efficiency on mobile devices. In this Mobile AI challenge, we address this problem and propose the participants to design an end-to-end real-time video super-resolution solution for mobile NPUs optimized for low energy consumption. The participants were provided with the REDS training dataset containing video sequences for a 4X video upscaling task. The runtime and power efficiency of all models was evaluated on the powerful MediaTek Dimensity 9000 platform with a dedicated AI processing unit capable of accelerating floating-point and quantized neural networks. All proposed solutions are fully compatible with the above NPU, demonstrating an up to 500 FPS rate and 0.2 [Watt / 30 FPS] power consumption. A detailed description of all models developed in the challenge is provided in this paper.

现有的二进制神经网络（BNN）主要在具有二进制功能的局部卷积上运作。但是，这种简单的位操作缺乏建模上下文依赖性的能力，这对于学习视觉模型中的歧视性深度表示至关重要。在这项工作中，我们通过介绍二进制神经模块的新设计来解决这个问题，这使BNN能够学习有效的上下文依赖性。首先，我们建议二进制多层感知器（MLP）块作为二进制卷积块的替代方案，以直接建模上下文依赖性。短距离和远程特征依赖性均由二进制MLP建模，其中前者提供局部电感偏置，后者在二元卷积中有限的接受场有限。其次，为了提高具有上下文依赖性的二进制模型的鲁棒性，我们计算上下文动态嵌入，以确定一般二进制卷积块中的二进化阈值。用我们的二进制MLP块和改进的二进制卷积，我们用明确的上下文依赖性建模构建了BNN，称为BCDNET。在标准Imagenet-1K分类基准上，BCDNET可实现72.3％的TOP-1准确性，并且优于领先的二进制方法的差距很大。尤其是，提出的BCDNET超过了最新的ReactNet-A，具有相似操作的2.9％TOP-1准确性。我们的代码可从https://github.com/sense-gvt/bcdn获得

归纳链路预测（ILP）是考虑到新兴知识图（kgs）中未见实体的联系，考虑到KGS的发展性质。一个更具挑战性的场景是，新兴的kg仅由看不见的实体组成，被称为已断开新兴kgs（DEKGS）。 DEKGS的现有研究仅专注于预测封闭链接，即预测新兴KG内部的联系。到目前为止，先前的工作尚未对将进化信息从原始KG到DEKG进行进化信息。为了填补空白，我们提出了一个名为DEKG-ILP的新型模型（由以下两个组成部分组成的dekg-ilp（断开新兴知识图形的归纳链路预测）。 （1）模块CLRM（基于对比的关系特定特征特征建模）是为了提取基于全球关系的语义特征而开发的，它们在原始KGS和DEKGS之间以新颖的采样策略共享。 （2）提出了模块GSM（基于GNN的子图建模），以提取围绕KGS中每个链接的局部子图拓扑信息。在几个基准数据集上进行的广泛实验表明，与最新方法相比，DEKG-ILP具有明显的性能改进，用于封闭和桥接链路预测。源代码可在线获得。

在过去的几十年中，出现了一种趋势，指出在可移动，可编程和可转换机制中利用结构不稳定性。受钢制发夹的启发，我们将面板组件与可靠的结构相结合，并使用半刚性塑料板建造合规的拍打机构，并将其安装在束缚的气动软机器人鱼和无螺旋螺旋式的电动机驱动器上，以展示它的前所未有的优势。设计规则是根据理论和验证提出的。观察到与参考相比，气动鱼的游泳速度提高了两倍，对Untether Fish的进一步研究表明，对于不固定的兼容的游泳运动员，可损坏的速度为2.03 BL/S（43.6 cm/s），优于先前报告的最快的，其幅度为194％。这项工作可能预示着下一代符合下一代机器人技术的结构革命。

基于循证或数据驱动的动态治疗方案对于个性化医学至关重要，这可以受益于离线增强学习（RL）。尽管可以在医疗机构之间获得大量医疗保健数据，但由于隐私限制，它们被禁止共享。此外，异质性存在于不同的站点。结果，需要联合的离线RL算法，并且有望解决这些问题。在本文中，我们提出了一个多站点的马尔可夫决策过程模型，该模型允许跨站点的均质和异质效应。提出的模型使对站点级特征的分析成为可能。我们设计了具有样本复杂性的离线RL的第一个联合政策优化算法。所提出的算法是通信效率和隐私性的，它仅需要通过交换摘要统计信息进行一轮通信交互。我们为所提出的算法提供理论保证，而没有足够的动作覆盖率，在这种情况下，学到的策略的次优率与速率相当，就好像数据没有分布一样。广泛的模拟证明了拟议算法的有效性。该方法应用于多个站点中的败血症数据集，以说明其在临床环境中的使用。

近年来，神经网络授权的演员 - 评论家（AC）算法具有重大的经验成功。然而，AC算法的大多数现有的理论支持集中于线性函数近似或线性化神经网络的情况，其中特征表示在整个训练中都是固定的。这种限制未能捕获神经AC中的表示学习的关键方面，这在实际问题中是关键的。在这项工作中，我们采取了一种含义的基于特征神经交流的演变和融合的视角。具体而言，我们考虑一个AC的版本，其中Actor和批评者由过度分辨率的双层神经网络表示，并以两时间测定的学习速率更新。批评评论批评者通过时间差异（TD）学习使用较大的步骤，而演员通过近端策略优化（PPO）更新，具有较小的步骤。在连续时间和无限宽度限制性方案中，当时间尺度适当分开时，我们证明了神经通讯以Sublinear率找到全球最佳政策。此外，我们证明了批评网络引起的特征表示允许在初始概念的邻域内发展。