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In introductory programming courses, it is challenging for instructors to provide debugging feedback on students' incorrect programs. Some recent tools automatically offer program repair feedback by identifying any differences between incorrect and correct programs, but suffer from issues related to scalability, accuracy, and cross-language portability. This paper presents FAPR -- our novel approach that suggests repairs based on program differences in a fast and accurate manner. FAPR is different from current tools in three aspects. First, it encodes syntactic information into token sequences to enable high-speed comparison between incorrect and correct programs. Second, to accurately extract program differences, FAPR adopts a novel matching algorithm that maximizes token-level matches and minimizes statement-level differences. Third, FAPR relies on testing instead of static/dynamic analysis to validate and refine candidate repairs, so it eliminates the language dependency or high runtime overhead incurred by complex program analysis. We implemented FAPR to suggest repairs for both C and C++ programs; our experience shows the great cross-language portability of FAPR. More importantly, we empirically compared FAPR with a state-of-the-art tool Clara. FAPR suggested repairs for over 95.5% of incorrect solutions. We sampled 250 repairs among FAPR's suggestions, and found 89.6% of the samples to be minimal and correct. FAPR outperformed Clara by suggesting repairs for more cases, creating smaller repairs, producing higher-quality fixes, and causing lower runtime overheads. Our results imply that FAPR can potentially help instructors or TAs to effectively locate bugs in incorrect code, and to provide debugging hints/guidelines based on those generated repairs., Comment: 12 pages, 5 figures for main text; 3 pages, 5 figures for appendix

Emerging technologies such as digital twins and 6th Generation mobile networks (6G) have accelerated the realization of edge intelligence in Industrial Internet of Things (IIoT). The integration of digital twin and 6G bridges the physical system with digital space and enables robust instant wireless connectivity. With increasing concerns on data privacy, federated learning has been regarded as a promising solution for deploying distributed data processing and learning in wireless networks. However, unreliable communication channels, limited resources, and lack of trust among users, hinder the effective application of federated learning in IIoT. In this paper, we introduce the Digital Twin Wireless Networks (DTWN) by incorporating digital twins into wireless networks, to migrate real-time data processing and computation to the edge plane. Then, we propose a blockchain empowered federated learning framework running in the DTWN for collaborative computing, which improves the reliability and security of the system, and enhances data privacy. Moreover, to balance the learning accuracy and time cost of the proposed scheme, we formulate an optimization problem for edge association by jointly considering digital twin association, training data batch size, and bandwidth allocation. We exploit multi-agent reinforcement learning to find an optimal solution to the problem. Numerical results on real-world dataset show that the proposed scheme yields improved efficiency and reduced cost compared to benchmark learning method.

Deep reinforcement learning (RL) has achieved outstanding results in recent years, which has led a dramatic increase in the number of methods and applications. Recent works are exploring learning beyond single-agent scenarios and considering multi-agent scenarios. However, they are faced with lots of challenges and are seeking for help from traditional game-theoretic algorithms, which, in turn, show bright application promise combined with modern algorithms and boosting computing power. In this survey, we first introduce basic concepts and algorithms in single agent RL and multi-agent systems; then, we summarize the related algorithms from three aspects. Solution concepts from game theory give inspiration to algorithms which try to evaluate the agents or find better solutions in multi-agent systems. Fictitious self-play becomes popular and has a great impact on the algorithm of multi-agent reinforcement learning. Counterfactual regret minimization is an important tool to solve games with incomplete information, and has shown great strength when combined with deep learning., Comment: 14 pages, review. Reorganizing the expressions in part of introduction and background