10,781 research outputs found

    Symbolic Simulation of Dataflow Synchronous Programs with Timers

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    International audienceThe synchronous language Lustre and its descendants have long been used to program and model discrete controllers. Recent work shows how to mix discrete and continuous elements in a Lustre-like language called Zélus. The resulting hybrid programs are deterministic and can be simulated with a numerical solver. In this article, we focus on a subset of hybrid programs where continuous behaviors are expressed using timers, nondeterministic guards, and invariants, as in Timed Safety Automata. We propose a source-to-source compilation pass to generate discrete code that, coupled with standard operations on Difference-Bound Matrices, produces symbolic traces that each represent a set of concrete traces

    Computer Mediated Communication and the Connection between Virtual Utopias and Actual Realities

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    People have generally been very ambivalent about the potential future roles of new technologies (and the internet specifically) and their possible effects on human society. Indeed, there has been a tendency for polarization between attitudes or perceptions of naive enthusiasm and cynical resistance towards the use of computers and computer networks, and for such related concepts as ‘the information superhighway’ and ‘cyberspace’. The projection of such ambivalent perceptions into naively utopian (or even ironically dystopian) images and narratives might be seen as the latest and uniquely global permutation of a basic function of human culture - that is, to imagine ‘a better future’ or represent ‘an ideal past’. This paper will consider the extent to which the kinds of virtual utopias made possible by computer-mediated communications are\ud ‘connected’ to the actual individual and social realities of human participants. In other words, how important might it be to recognise a distinction between the use of virtual utopias (and utopian representations in any culture) as merely escapist, self-indulgent fantasy on one hand, and\ud as a useful, transformative media for reinventing the human condition on the other? Whether we live in a Panoptic or democratic Net ten years from now depends, in no small measure, on what you and I know and do now. Howard Rheingold, Afterword to The Virtual Community (1994, p. 310

    A Method to Identify and Analyze Biological Programs through Automated Reasoning.

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    Predictive biology is elusive because rigorous, data-constrained, mechanistic models of complex biological systems are difficult to derive and validate. Current approaches tend to construct and examine static interaction network models, which are descriptively rich but often lack explanatory and predictive power, or dynamic models that can be simulated to reproduce known behavior. However, in such approaches implicit assumptions are introduced as typically only one mechanism is considered, and exhaustively investigating all scenarios is impractical using simulation. To address these limitations, we present a methodology based on automated formal reasoning, which permits the synthesis and analysis of the complete set of logical models consistent with experimental observations. We test hypotheses against all candidate models, and remove the need for simulation by characterizing and simultaneously analyzing all mechanistic explanations of observed behavior. Our methodology transforms knowledge of complex biological processes from sets of possible interactions and experimental observations to precise, predictive biological programs governing cell function

    Exploiting the Temporal Logic Hierarchy and the Non-Confluence Property for Efficient LTL Synthesis

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    The classic approaches to synthesize a reactive system from a linear temporal logic (LTL) specification first translate the given LTL formula to an equivalent omega-automaton and then compute a winning strategy for the corresponding omega-regular game. To this end, the obtained omega-automata have to be (pseudo)-determinized where typically a variant of Safra's determinization procedure is used. In this paper, we show that this determinization step can be significantly improved for tool implementations by replacing Safra's determinization by simpler determinization procedures. In particular, we exploit (1) the temporal logic hierarchy that corresponds to the well-known automata hierarchy consisting of safety, liveness, Buechi, and co-Buechi automata as well as their boolean closures, (2) the non-confluence property of omega-automata that result from certain translations of LTL formulas, and (3) symbolic implementations of determinization procedures for the Rabin-Scott and the Miyano-Hayashi breakpoint construction. In particular, we present convincing experimental results that demonstrate the practical applicability of our new synthesis procedure
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