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The Maximum Satisfiability (MAXSAT) problem is an optimization version of the Satisfiability problem (SAT) in which one is given a CNF formula with $n$ variables and needs to find the maximum number of simultaneously satisfiable clauses. The recent works of Xiao [IJCAI 2022], Xu et al. [IJCAI 2019], Alferov and Bliznets [AAAI 2021] achieved significant progress in proving new upper bounds on the worst-case computational complexity of MAXSAT. All three works reduce general MAXSAT to a special case of MAXSAT where each variable appears a small number of times. So, it is important to design fast algorithms for $(n,k)$-MAXSAT to construct an efficient exact algorithm for MAXSAT. $(n,k)$-MAXSAT is a special case of MAXSAT where each variable appears at most $k$ times in the input formula. 
For the $(n,3)$-MAXSAT problem, we design a $O^*(1.1749^n)$ algorithm improving on the previous record running time of $O^*(1.191^n)$ (Belova and Bliznets [TCS 2020]). For the $(n,4)$-MAXSAT problem, we construct a $O^*(1.3803^n)$ algorithm improving on the previous best running time of $O^*(1.4254^n)$ (Alferov and Bliznets [AAAI - 2021]). Using the results, we develop a $O^*(1.0911^L)$ algorithm for the MAXSAT where $L$ is a length of the input formula which improves $O^*(1.0927^L)$ algorithm by Alferov and Bliznets [AAAI - 2021].

AAAI 2023

Improved Algorithms for Maximum Satisfiability and Its Special Cases

exact exponential algorithms

maxsat

optimization

The purpose of the AAAI conference series is to promote research in Artificial Intelligence (AI) and foster scientific exchange between researchers, practitioners, scientists, students, and engineers across the entirety of AI and its affiliated disciplines. AAAI-23 is the Thirty-Seventh AAAI Conference on Artificial Intelligence. The theme of this conference is to create collaborative bridges within and beyond AI. Like previous AAAI conferences, AAAI-23 will feature technical paper presentations, special tracks, invited speakers, workshops, tutorials, poster sessions, senior member presentations, competitions, and exhibit programs, and two new activities: a Bridge Program and a Lab Program. Many of these activities are tailored to the theme of bridges and all are selected according to the highest standards, with additional programs for students and young researchers. 
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The purpose of the AAAI conference series is to promote research in Artificial Intelligence (AI) and foster scientific exchange between researchers, practitioners, scientists, students, and engineers across the entirety of AI and its affiliated disciplines.

poster

Structure learning is a core problem in AI central to the fields of neuro-symbolic AI and statistical relational learning. It consists in automatically learning a logical theory from data. The basis for structure learning is mining repeating patterns in the data, known as structural motifs. Finding these patterns reduces the exponential search space and therefore guides the learning of formulas. Despite the importance of motif learning, it is still not well understood. We present the first principled approach for mining structural motifs in lifted graphical models, 
languages that blend first-order logic with probabilistic models,  which uses a stochastic process to measure the similarity of entities in the data. 

Our first contribution is an algorithm, which depends on two intuitive hyperparameters: one controlling the uncertainty in the entity similarity measure, and one controlling the softness of the resulting rules. Our second contribution is a preprocessing step where we perform hierarchical clustering on the data to reduce the search space to the most relevant data. Our third contribution is to introduce an O(n ln(n)) (in the size of the entities in the data) algorithm for clustering structurally-related data. We evaluate our approach using standard benchmarks and show that we outperform state-of-the-art structure learning approaches by up to 6% in terms of accuracy and up to 80% in terms of runtime.

Principled and Efficient Motif Finding for Structure Learning in Lifted Graphical Models

Traffic classification is a critical task in network security and management since it allows for the monitoring and analyzing of metadata in the network. Recent research has demonstrated the effectiveness of the deep learning-based traffic classification method. However, the following limitations remain: (1) the traffic representation is simply generated from raw packet bytes, resulting in the absence of important information; (2) the model structure of directly applying deep learning algorithms does not take traffic characteristics into account; and (3) scenario-specific classifier training usually requires a labor-intensive and time-consuming process to label data. In this paper, we introduce a masked autoencoder (MAE) based traffic transformer with multi-level flow representation to tackle these problems. To model raw traffic data, we design a formatted traffic representation matrix with hierarchical flow information. After that, we develop an efficient Traffic Transformer, in which packet-level and flow-level attention mechanisms implement more efficient feature extraction with lower complexity. At last, we utilize MAE paradigm to pre-train our classifier with a large amount of unlabeled data, and perform fine-tuning with a few labeled data for a series of traffic classification tasks. Experiment findings reveal that our method outperforms state-of-the-art methods on five real-world traffic datasets by a large margin. The code is available at https://github.com/NSSL-SJTU/YaTC.

Yet Another Traffic Classifier: A Masked Autoencoder Based Traffic Transformer with Multi-Level Flow Representation

Traditional federated learning (FL) algorithms, such as FedAvg, fail to handle non-i.i.d data because they learn a global model by simply averaging biased local models that are trained on non-i.i.d local data, therefore failing to model the global data distribution. 
In this paper, we present a novel Bayesian FL algorithm that successfully handles such a non-i.i.d FL setting by enhancing the local training task with an auxiliary task that explicitly estimates the global data distribution. 
One key challenge in estimating the global data distribution is that the data are partitioned in FL, and therefore the ground-truth global data distribution is inaccessible.
To address this challenge, we propose an expectation-propagation-inspired probabilistic neural network, dubbed federated neural propagation (FedNP), which efficiently estimates the global data distribution given non-i.i.d data partitions. Our algorithm is sampling-free and end-to-end differentiable, can be applied with any conventional FL frameworks and learns richer global data representation.
Experiments on both image classification tasks with synthetic non-i.i.d image data partitions and real-world non-i.i.d speech recognition tasks demonstrate that our framework effectively alleviates the performance deterioration caused by non-i.i.d data.

FedNP: Towards Non-IID Federated Learning via Federated Neural Propagation

Audio-visual speech recognition (AVSR) has gained remarkable success for ameliorating the noise-robustness of speech recognition. Mainstream methods focus on fusing audio and visual inputs to obtain modality-invariant representations. However, such representations are prone to over-reliance on audio modality as it is much easier to recognize than video modality in clean conditions. As a result, the AVSR model underestimates the importance of visual stream in face of noise corruption. To this end, we leverage visual modality-specific representations to provide stable complementary information for the AVSR task. Specifically, we propose a reinforcement learning (RL) based framework called MSRL, where the agent dynamically harmonizes modality-invariant and modality-specific representations in the auto-regressive decoding process. We customize a reward function directly related to task-specific metrics (i.e., word error rate), which encourages the MSRL to effectively explore the optimal integration strategy. Experimental results on the LRS3 dataset show that the proposed method achieves state-of-the-art in both clean and various noisy conditions. Furthermore, we demonstrate the better generality of MSRL system than other baselines when test set contains unseen noises.    

Leveraging Modality-specific Representations for Audio-visual Speech Recognition via Reinforcement Learning

Multi-task learning (MTL) models have demonstrated impressive results in computer vision, natural language processing and recommender systems. However, how MTL balances the optimization of shared parameters has not been explored yet.  In this work, we quantify the dominance of parameter training in MTL and demonstrate that dominance still occurs in existing works and leads to optimization problems using adaptive learning rate methods for optimization. We propose a Task-aware Adaptive Learning Rate method, named AdaTask, to use task-specific accumulative gradients when adjusting the learning rate of each parameter. Specifically, for tasks with a large accumulative gradient of parameters, a small learning rate is required; otherwise, for tasks with a small accumulative gradient, a large learning rate is required. Our approach can be treated as balancing the loss between tasks at parameter level. We demonstrate that task dominance is resolved by our method using our proposed task dominance quantification metric. Comprehensive experiments on synthetic and three real-world datasets show that AdaTask achieves better performance compared with several state-of-the-art MTL approaches.

AdaTask: A Task-aware Adaptive Learning Rate Approach to Multi-task Learning

Bilevel Optimization Programming is used to model complex and conflicting interactions between agents, for example in Robust AI or Privacy preserving AI. Integrating bilevel mathematical programming within deep learning is thus an essential objective for the Machine Learning community. 
Previously proposed approaches only consider single-level programming. In this paper, we extend existing single-level optimization programming approaches and thus propose Differentiating through Bilevel Optimization Programming (BiGrad) for end-to-end learning of models that use Bilevel Programming as a layer. 
BiGrad has wide applicability and can be used in modern machine learning frameworks. BiGrad is applicable to both continuous and combinatorial Bilevel optimization problems. We describe a class of gradient estimators for the combinatorial case which reduces the requirements in terms of computation complexity; for the case of the continuous variable, the gradient computation takes advantage of the push-back approach (i.e. vector-jacobian product) for an efficient implementation. Experiments show that the BiGrad successfully extends existing single-level approaches to Bilevel Programming.

Implicit Bilevel Optimization: Differentiating through Bilevel Optimization Programming

THMA: Tencent HD map AI System for Creating HD Map Annotations

Low-light video enhancement (LLVE) is an important yet challenging task with many applications such as photographing and autonomous driving. Unlike single image low-light enhancement, most LLVE methods utilize temporal information from adjacent frames to restore the color and remove the noise of the target frame. However, these algorithms, based on the framework of multi-frame alignment and enhancement, may produce multi-frame fusion artifacts when encountering extreme low light or fast motion. In this paper, inspired by the low latency and high dynamic range of events, we use synthetic events from multiple frames to guide the enhancement and restoration of low-light videos. Our method contains three stages: 1) event synthesis and enhancement, 2) event and image fusion, and 3) low-light enhancement. In this framework, we design two novel modules (event-image fusion transform and event-guided dual branch) for the second and third stages, respectively. Extensive experiments show that our method outperforms existing low-light video or single image enhancement approaches on both synthetic and real LLVE datasets.

Low-Light Video Enhancement with Synthetic Event Guidance

Existing space-time video super-resolution (ST-VSR) methods fail to achieve high-quality reconstruction since they fail to fully explore the spatial-temporal correlations, long-range components in particular. Although the recurrent structure for ST-VSR adopts bidirectional propagation to aggregate information from the entire video, collecting the temporal information between the past and future via one-stage representations inevitably loses the long-range relations. To alleviate the limitation, this paper proposes an immediate storeand-fetch network to promote long-range correlation learning, where the stored information from the past and future can be refetched to help the representation of the current
frame. Specifically, the proposed network consists of two modules: a backward recurrent module (BRM) and a forward recurrent module (FRM). The former first performs backward inference from future to past, while storing future super-resolution (SR) information for each frame. Following that, the latter performs forward inference from past to future to super-resolve all frames, while storing past SR information for each frame. Since FRM inherits SR information from BRM, therefore, spatial and temporal information from the entire video sequence is immediately stored and fetched, which allows drastic improvement for ST-VSR. Extensive experiments both on ST-VSR and space video super-resolution
(S-VSR) as well as time video super-resolution (T-VSR) have demonstrated the effectiveness of our proposed method over other state-of-the-art methods on public datasets.

Store and Fetch Immediately: Everything Is All You Need for Space-Time Video Super-Resolution

In this paper, we propose Stochastic Knowledge Distillation (SKD) to obtain compact BERT-style language model dubbed SKDBERT. In each distillation iteration, SKD samples a teacher model from a pre-defined teacher team, which consists of multiple teacher models with multi-level capacities, to transfer knowledge into student model in an one-to-one manner. Sampling distribution plays an important role in SKD. We heuristically present three types of sampling distributions to assign appropriate probabilities for multi-level teacher models. SKD has two advantages: 1) it can preserve the diversities of multi-level teacher models via stochastically sampling single teacher model in each distillation iteration, and 2) it can also improve the efficacy of knowledge distillation via multi-level teacher models when large capacity gap exists between the teacher model and the student model. Experimental results on GLUE benchmark show that SKDBERT reduces the size of a BERT$_{\rm BASE}$ model by 40% while retaining 99.5% performances of language understanding and being 100% faster. 

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Principled and Efficient Motif Finding for Structure Learning in Lifted Graphical Models

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