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1. Trace-Guided Inductive Synthesis of Recursive Functional Programs

   https://doi.org/10.1145/3591255  

   Yuan, Yongwei; Radhakrishna, Arjun; Samanta, Roopsha (June 2023, Proceedings of the ACM on Programming Languages)

   We propose a novel trace-guided approach to tackle the challenges of ambiguity and generalization in synthesis of recursive functional programs from input-output examples. Our approach augments the search space of programs with recursion traces consisting of recursive subcalls of the programs. Our method is based on a new version space algebra (VSA) for succinct representation and efficient manipulation of pairs of recursion traces and programs that are consistent with each other. We have implemented this approach in a tool called SyRup and evaluated it on benchmarks from prior work. Our evaluation demonstrates that SyRup not only requires fewer examples to achieve a certain success rate than existing synthesizers, but is also less sensitive to the quality of the examples. 

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2. Cache automaton

   https://doi.org/10.1145/3123939.3123986  

   Subramaniyan, Arun; Wang, Jingcheng; Balasubramanian, Ezhil R.; Blaauw, David; Sylvester, Dennis; Das, Reetuparna (October 2017, MICRO-50 '17 Proceedings of the 50th Annual IEEE/ACM International Symposium on Microarchitecture)

   Finite State Automata are widely used to accelerate pattern matching in many emerging application domains like DNA sequencing and XML parsing. Conventional CPUs and compute-centric accelerators are bottlenecked by memory bandwidth and irregular memory access patterns in automata processing. We present Cache Automaton, which repurposes last-level cache for automata processing, and a compiler that automates the process of mapping large real world Non-Deterministic Finite Automata (NFAs) to the proposed architecture. Cache Automaton extends a conventional last-level cache architecture with components to accelerate two phases in NFA processing: state-match and state-transition. State-matching is made efficient using a sense-amplifier cycling technique that exploits spatial locality in symbol matches. State-transition is made efficient using a new compact switch architecture. By overlapping these two phases for adjacent symbols we realize an efficient pipelined design. We evaluate two designs, one optimized for performance and the other optimized for space, across a set of 20 diverse benchmarks. The performance optimized design provides a speedup of 15× over DRAM-based Micron's Automata Processor and 3840× speedup over processing in a conventional x86 CPU. The proposed design utilizes on an average 1.2MB of cache space across benchmarks, while consuming 2.3nJ of energy per input symbol. Our space optimized design can reduce the cache utilization to 0.72MB, while still providing a speedup of 9× over AP. 

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3. Alternating Good-for-MDPs Automata

   https://doi.org/10.1007/978-3-031-19992-9_19  

   Hahn, Ernst Moritz; Perez, Mateo; Schewe, Sven; Somenzi, Fabio; Trivedi, Ashutosh; Wojtczak, Dominik (October 2022, International Symposium on Automated Technology for Verification and Analysis (ATVA 2022))

   Bouajjani, A.; Holík, L.; Wu, Z. (Ed.)

   When omega-regular objectives were first proposed in model-free reinforcement learning (RL) for controlling MDPs, deterministic Rabin automata were used in an attempt to provide a direct translation from their transitions to scalar values. While these translations failed, it has turned out that it is possible to repair them by using good-for-MDPs (GFM) Buechi automata instead. These are nondeterministic Buechi automata with a restricted type of nondeterminism, albeit not as restricted as in good-for-games automata. Indeed, deterministic Rabin automata have a pretty straightforward translation to such GFM automata, which is bi-linear in the number of states and pairs. Interestingly, the same cannot be said for deterministic Streett automata: a translation to nondeterministic Rabin or Buechi automata comes at an exponential cost, even without requiring the target automaton to be good-for-MDPs. Do we have to pay more than that to obtain a good-for-MDPs automaton? The surprising answer is that we have to pay significantly less when we instead expand the good-for-MDPs property to alternating automata: like the nondeterministic GFM automata obtained from deterministic Rabin automata, the alternating good-for-MDPs automata we produce from deterministic Streett automata are bi-linear in the size of the deterministic automaton and its index. They can therefore be exponentially more succinct than the minimal nondeterministic Buechi automaton. 

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4. Deciding Differential Privacy of Online Algorithms with Multiple Variables

   https://doi.org/10.1145/3576915.3623170  

   Chadha, Rohit; Sistla, A Prasad; Viswanathan, Mahesh; Bhusal, Bishnu (November 2023, ACM CCS '23: Proceedings of the 2023 ACM SIGSAC Conference on Computer and Communications Security)

   We consider the problem of checking the differential privacy of online randomized algorithms that process a stream of inputs and produce outputs corresponding to each input. This paper generalizes an automaton model called DiP automata [10] to describe such algorithms by allowing multiple real-valued storage variables. A DiP automaton is a parametric automaton whose behavior depends on the privacy budget ∈. An automaton A will be said to be differentially private if, for some D, the automaton is D∈-differentially private for all values of ∈ > 0. We identify a precise characterization of the class of all differentially private DiP automata. We show that the problem of determining if a given DiP automaton belongs to this class is PSPACE-complete. Our PSPACE algorithm also computes a value for D when the given automaton is differentially private. The algorithm has been implemented, and experiments demonstrating its effectiveness are presented. 

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5. An Impossibility Result in Automata-Theoretic Reinforcement Learning.

   https://doi.org/10.1007/978-3-031-19992-9_3  

   Hahn, Ernst Moritz; Perez, Mateo; Schewe, Sven; Somenzi, Fabio; Trivedi, Ashutosh; Wojtczak, Dominik (October 2022, International Symposium on Automated Technology for Verification and Analysis (ATVA 2022))

   Bouajjani, A.; Holík, L.; Wu, Z. (Ed.)

   The expanding role of reinforcement learning (RL) in safety-critical system design has promoted omega-automata as a way to express learning requirements—often non-Markovian—with greater ease of expression and interpretation than scalar reward signals. When 𝜔-automata were first proposed in model-free RL, deterministic Rabin acceptance conditions were used in an attempt to provide a direct translation from omega-automata to finite state “reward” machines defined over the same automaton structure (a memoryless reward translation). While these initial attempts to provide faithful, memoryless reward translations for Rabin acceptance conditions remained unsuccessful, translations were discovered for other acceptance conditions such as suitable, limit-deterministic Buechi acceptance or more generally, good-for-MDP Buechi acceptance conditions. Yet, the question “whether a memoryless translation of Rabin conditions to scalar rewards exists” remained unresolved. This paper presents an impossibility result implying that any attempt to use Rabin automata directly (without extra memory) for model-free RL is bound to fail. To establish this result, we show a link between a class of automata enabling memoryless reward translation to closure properties of its accepting and rejecting infinity sets, and to the insight that both the property and its complement need to allow for positional strategies for such an approach to work. We believe that such impossibility results will provide foundations for the application of RL to safety-critical systems. 

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