Sofiène Tahar

Concordia University Montreal, Montréal, Quebec, Canada

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Publications (283)60.63 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Image processing and computer vision applications are usually complex in terms of the large amount of processed data and high computation loads. To cope with this, optimization techniques and high-performance hardware platforms are required. Since these applications present many opportunities for parallelism, heterogeneous parallel platforms (HPPs) are an interesting choice, offering a good balance between high computation capabilities and flexibility to handle a large spectrum of application features. Applications such as image filtering and edge detection make extensive use of finite difference method to solve partial derivative equations, which computational pattern is called stencil computation. Stencil computations are known as memory-bound, so that reducing high-latency memory access becomes the biggest challenge to reach high performance. In this paper, we present our methodology as a basis of a performance tuning framework to optimize the implementation of multiple stencil computations on HPPs. Results show that our approach outperforms SDK-based methodologies, improving performance. Moreover, using the proposed approach, the developer has the ability of investigating efficiently the performance of the stencil computations before implementing actual code on the target platforms.
    No preview · Article · Nov 2015 · The Journal of Supercomputing
  • Sidi Mohamed Beillahi · Umair Siddique · Sofiène Tahar
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    ABSTRACT: Power electronics is an active area of research which has widespread applications in safety and cost critical domains such as power grids, biomedical devices and avionics systems. The complexity of power electronic systems is rapidly reaching a point where it will become difficult to verify the correctness and robustness of underlying designs. In this paper, we propose to use a recent formalization of signal-flow-graphs in higher-order-logic for the formal analysis of power electronic converters, which are the foremost components of modern power electronic systems. In particular, we demonstrate the necessary steps to formally reason about the critical properties (e.g., efficiency, stability and resonance) of power electronic converters by using their corresponding signal-flowgraph based high-level models. In order to demonstrate the utilization of the proposed infrastructure, we present the formal analysis of a couple of widely used power converters, namely a pulse width modulation push-pull DC-DC converter and a 1-boost cell DC-DC converter.
    No preview · Chapter · Nov 2015
  • Henda Aridhi · Mohamed H. Zaki · Sofiène Tahar
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    ABSTRACT: The reduction of the computational cost of statistical circuit analysis, such as Monte Carlo (MC) simulation, is a challenging problem. In this paper, we propose to build macromodels capable of reproducing the statistical behavior of all repeated MC simulations in a single simulation run. The parameter space is sampled similarly to the MC method and the resulting nonlinear models are reduced simultaneously to a small macromodel using nonlinear model order reduction method based on projection, perturbation theory and linearization techniques. We demonstrate the effectiveness of the proposed method for three applications: a current mirror, an operational transconductance amplifier, and a three inverter chain under the effect of current factor and threshold voltage variations. Our experimental results show that our method provides a speedup in the range 100–500 over 1000 samples of MC simulation.
    No preview · Article · Jul 2015 · Analog Integrated Circuits and Signal Processing
  • Tarek Mhamdi · Osman Hasan · Sofiène Tahar
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    ABSTRACT: Anonymity and confidentiality protocols constitute crucial parts in many network applications as they ensure anonymous communications between entities in a network or provide security in insecure communication channels. Evaluating the properties of these protocols is therefore of paramount importance, especially in the case of safety-critical applications. However, traditional analysis techniques, like simulation, cannot ascertain accurate analysis in this domain. We propose to overcome this limitation by conducting an information leakage analysis of anonymity and cryptographic protocols within the trusted kernel of a higher-order-logic theorem prover. For this purpose, we first introduce two novel measures of information leakage, namely the information leakage degree and the conditional information leakage degree and then present a higher-order-logic formalization of information measures and the underlying required theories of measure, probability and information. For illustration purposes, we use the proposed framework to evaluate the security properties of the one-time pad encryption system as well as the properties of an anonymity-based single MIX. We show how this formal analysis allowed us to find a counter-example for a theorem that was reported in the literature to describe the leakage properties of this single MIX.
    No preview · Article · Jun 2015 · Formal Methods in System Design
  • U. Siddique · O. Hasan · S. Tahar
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    ABSTRACT: The prominent advantages of photonics are high bandwidth, low power and the possibility of better electromagnetic interference immunity. As a result, photonics technology is increasingly used in ubiquitous applications such as telecommunication, medicine, avionics and robotics. One of the main critical requirements is to verify the corresponding functional properties of these systems. In this perspective, we identify the most widely used modeling techniques (e.g., transfer matrices, difference equations and block diagrams) for the modeling and analysis of photonic components. Considering the safety and cost critical nature of the application domain, we discuss the potential of using formal methods as a complementary analysis approach. In particular, we propose a framework to formally specify and verify the critical properties of complex photonic systems within the sound core of a higher-order-logic theorem prover. For illustration purposes, we present the formal specification of a microring resonator based photonic filter along with the verification of some important design properties such as spectral power and filtering rejection ratio.
    No preview · Article · Jun 2015
  • Umair Siddique · Osman Hasan · Sofiène Tahar
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    ABSTRACT: Fractional calculus is a generalization of classical theories of integration and differentiation to arbitrary order (i.e., real or complex numbers). In the last two decades, this new mathematical modeling approach has been widely used to analyze a wide class of physical systems in various fields of science and engineering. In this paper, we describe an ongoing project which aims at formalizing the basic theories of fractional calculus in the HOL Light theorem prover. Mainly, we present the motivation and application of such formalization efforts, a roadmap to achieve our goals, current status of the project and future milestones.
    No preview · Article · May 2015
  • Osman Hasan · Waqar Ahmed · Sofiène Tahar · Mohamed Salah Hamdi
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    ABSTRACT: Reliability Block Diagrams (RBDs) allow us to model the failure relationships of complex systems and their sub-components and are extensively used for system reliability, availability, dependability and maintainability analyses of many engineering systems. Traditionally, Reliability Block Diagrams (RBD) are analyzed using paper-and-pencil proofs or computer simulations. Recently, formal techniques, including Petri Nets and higher-order-logic theorem proving, have been used for their analysis as well. In this paper, we provide a concise survey of these available RBD analysis techniques and compare them based on their accuracy, user friendliness and computational requirements.
    No preview · Article · Mar 2015 · AIP Conference Proceedings
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    ABSTRACT: This paper presents an adaptive state of charge (SOC) and state of health (SOH) estimation technique for lithium-ion batteries. The adaptive strategy estimates online parameters of the battery model using a Lyapunov-based adaptation law. Therefore, the adaptive observer stability is guaranteed by Lyapunov's direct method. Since no a priori knowledge of battery parameters is required, accurate estimation is still achieved, although parameters change due to aging or other factors. Unlike other estimation strategies, only battery terminal voltage and current measurements are required. Simulation and experimental results highlight the high SOC and SOH accuracy estimation of the proposed technique.
    No preview · Article · Mar 2015 · IEEE Transactions on Industrial Electronics
  • U. Siddique · S. Tahar
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    ABSTRACT: The verification of optical systems is an important issue due to their safety and financial critical nature (e.g., laser surgeries and space telescopes). Theorem proving offers an attractive solution to overcome the accuracy and soundness problems of traditional approaches like paper-and-pencil based proofs and computer simulation. However, existing formalizations of optics theories do not provide the facility to analyze optical imaging systems which describe the behavior of light ray within the system. In this paper, we present the ray optics formalization of cardinal points which are the most fundamental requirement to model imaging properties of optical systems. We also present the verification of cardinal points for a general system consisting of any number of optical components. For illustration purposes, we present the formal analysis of a thick lens.
    No preview · Article · Feb 2015
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    ABSTRACT: Fast Health Interoperable Resources (FHIR) is the recently proposed standard from HL7. Its distinguishing features include the user friendly implementation, support of built-in terminologies and for widely-used web standards. Given the safety-critical nature of FHIR, the rigorous analysis of e-health systems using the FHIR is a dire need since they are prone to failures. As a first step towards this direction, we propose to use probabilistic model checking, i.e., a formal probabilistic analysis approach, to assess the reliability of a typical e-health system used in hospitals based on the FHIR standard. In particular, we use the PRISM model checker to analyze the Markov Decision Process (MDP) and Continuous Time Markov Chain (CTMC) models to assess the failure probabilities of the overall system.
    No preview · Article · Jan 2015

  • No preview · Conference Paper · Jan 2015
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    ABSTRACT: This chapter proposes a complementary formal-based solution to the verification of analog and mixed-signal (AMS) designs. The authors use symbolic computation to model and verify AMS designs through the application of induction-based model checking. They also propose the use of higher order logic theorem proving to formally verify continuous models of analog circuits. To test and validate the proposed approaches, they developed prototype implementations in Mathematica and HOL and target analog and mixed-signal systems such as delta-sigma modulators.
    No preview · Article · Jan 2015

  • No preview · Conference Paper · Jan 2015
  • Henda Aridhi · Mohamed H. Zaki · Sofiene Tahar

    No preview · Article · Jan 2015 · IEEE Transactions on Very Large Scale Integration (VLSI) Systems
  • Sohaib Ahmad · Osman Hasan · Umair Siddique · Sofiéne Tahar
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    ABSTRACT: The behavioral characterization of biological organisms is a fundamental requirement for both the understanding of the physiological properties and potential drug designs. One of the most widely used approaches in this domain is molecular pathways, which offers a systematic way to represent and analyze complex biological systems. Traditionally, such pathways are analyzed using paper-and-pencil based proofs and simulations. However, these methods cannot ascertain accurate analysis, which is a serious drawback for safety-critical applications (e.g., analysis of cancer cells and cerebral malarial network). In order to overcome these limitations, we recently proposed to formally reason about molecular pathways within the sound core of a theorem prover. As a first step towards this direction, we formally expressed three logical operators and four inference rules of Zsyntax , which is a deduction language for molecular pathways. In the current paper, we extend this formalization by verifying a couple of behavioral properties of Zsyntax based deduction using the HOL4 theorem prover. This verification not only ensures the correctness of our formalization of Zsyntax but also facilitates its usage for the formal reasoning about molecular pathways. For illustration purposes, we formally analyze a molecular reaction of the glycolytic pathway leading from D-Glucose to Fructose-1,6-bisphosphate.
    No preview · Chapter · Jan 2015
  • O. Hasan · S. Tahar
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    ABSTRACT: Scientists and engineers often have to deal with systems that exhibit random or unpredictable elements and must effectively evaluate probabilities in each situation. Computer simulations, while the traditional tool used to solve such problems, are limited in the scale and complexity of the problems they can solve. Formalized Probability Theory and Applications Using Theorem Proving discusses some of the limitations inherent in computer systems when applied to problems of probabilistic analysis, and presents a novel solution to these limitations, combining higher-order logic with computer-based theorem proving. Combining practical application with theoretical discussion, this book is an important reference tool for mathematicians, scientists, engineers, and researchers in all STEM fields.
    No preview · Article · Jan 2015
  • Vincent Aravantinos · Sofiene Tahar
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    ABSTRACT: Reducing the distance between informal and formal proofs in interactive theorem proving is a long-standing matter. An approach to this general topic is to increase automation in theorem provers: indeed, automation turns many small formal steps into one big step. In spite of the usual automation methods, there are still many situations where the user has to provide some information manually, whereas this information could be derived from the context. In this paper, we characterize some very common use cases where such situations happen, and identify some general patterns behind them. We then provide solutions to deal with these situations automatically, which we implemented as HOL Light and HOL4 tactics. We find these tactics to be extremely useful in practice, both for their automation and for the feedback they provide to the user.
    No preview · Conference Paper · Aug 2014
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    ABSTRACT: Quantum computers are promising to efficiently solve hard computational problems, especially NP problems. In this paper, we propose to tackle the formal verification of quantum circuits using theorem proving. In particular, we focus on the verification of quantum computing based on coherent light, which is typically light produced by laser sources. We formally verify the behavior of the quantum flip gate in HOL Light: we prove that it can flip a zero-quantum-bit to a one-quantum-bit and vice versa. To this aim, we model two optical devices: the beam splitter and the phase conjugating mirror and prove relevant properties about them. Then by cascading the two elements and utilizing these properties, the complete model of the flip gate is formally verified. This requires the formalization of some fundamental mathematics like exponentiation of linear transformations.
    No preview · Article · Jul 2014
  • Umair Siddique · Mohamed Yousri Mahmoud · Sofiène Tahar
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    ABSTRACT: System analysis based on difference or recurrence equations is the most fundamental technique to analyze biological, electronic, control and signal processing systems. Z-transform is one of the most popular tool to solve such difference equations. In this paper, we present the formalization of Z-transform to extend the formal linear system analysis capabilities using theorem proving. In particular, we use differential, transcendental and topological theories of multivariate calculus to formally define Z-transform in higher-order logic and reason about the correctness of its properties, such as linearity, time shifting and scaling in z-domain. To illustrate the practical effectiveness of the proposed formalization, we present the formal analysis of an infinite impulse response (IIR) digital signal processing filter.
    No preview · Article · Jul 2014
  • Umair Siddique · Sofiène Tahar
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    ABSTRACT: Recently, optics technology has emerged as a promising solution by resolving critical bottlenecks in conventional electronic systems. Its application domain spans over diverse fields ranging from laser surgeries to space telescopes. In this paper, we describe an ongoing project which aims at building a theorem proving based framework for the formal reasoning about geometrical optics, an essential theory required in the design and analysis of optical systems. Mainly, we present the motivation of our work, a road-map to achieve our goals, current status of the project and future milestones.
    No preview · Article · Jul 2014

Publication Stats

2k Citations
60.63 Total Impact Points

Institutions

  • 1970-2015
    • Concordia University Montreal
      • Department of Electrical and Computer Engineering
      Montréal, Quebec, Canada
  • 1996-2007
    • Université de Montréal
      • Department of Computer Science and Operations Research
      Montréal, Quebec, Canada
  • 2001
    • Middlesex University, UK
      • Department of Computer Science
      London, ENG, United Kingdom