Peter Bunus

Modelica - a general object-oriented language for continuous and discrete-event system modeling and simulation

Modelica is a general equation-based object-oriented language for continuous and discrete-event modeling of physical systems for the purpose of efficient simulation. The language unifies and generalizes previous object-oriented modeling languages. It is bringing about a revolution in this area, based on its ease of use, visual design of models with combination of Lego-like predefined model building blocks, its ability to define model libraries with re-usable components and its support for modeling and simulation of complex applications involving parts from several application domains. In this paper we present the Modelica language with emphasis on its language features and one of the associated simulation environments. Simulation models can be developed in an integrated problem-solving environment by using a graphical editor for connection diagrams. Connections are established just by drawing lines between objects picked from a class library. The principles of object oriented physical systems modeling and the multi-domain capabilities of the language are presented in the paper by several examples.

A simulation and decision framework for selection of numerical solvers in scientific computing

Selecting the right numerical solver or the most appropriate numerical package for a particular simulation problem it is increasingly difficult for users without an extensive mathematical background and deeper knowledge in numerical analysis. In this paper, we propose a model-driven combined decision-simulation framework for automatically selecting a numerical method for a given set of equation system. We also propose a formal paradigm based on domain-specific languages for specification of structural and behavioral aspects of the numerical equation solving process. Starting from a declarative description of the equation system that need to be solved, our system is able to detect the nature of the equations, perform symbolic manipulations of the equations, and transform them into a domain-specific model. We describe the motivation for such a system, its main features, and a prototype environment together with a usage example.

Automated Static Analysis of Equation-Based Components

Mathematical modeling and the simulation of complex physical systems are emerging as key technologies in engineering. The availability of static analyzers and automatic debuggers for detecting structural and numerical inconsistencies in the simulation models is crucial. To address this need, the authors propose a methodology for detecting and repairing overconstrained and underconstrained situations based on graph-theoretical approaches. Components and equations that cause the irregularities are automatically isolated, and meaningful error messages for the user are elaborated. The authors have implemented the AMOEBA (Automatic Modelica Equation-Based Analyzer) environment to support the development and specification of correct equation-based simulation models by applying graph-theoretical approaches and semiautomatic debugging techniques. The implementation architecture and preliminary experiments with a prototype debugger integrated in the symbolic and numeric engine, ModSimPack, of the Modelica language compiler are presented and discussed.

Semi-automatic fault localization and behavior verification for physical system simulation models

Mathematical modeling and simulation of complex physical systems are emerging as key technologies in engineering. Modern approaches to physical system simulation allow users to specify simulation models with the help of equation-based languages. Due to the high-level declarative abstraction of these languages program errors are extremely hard to find. This paper presents an algorithmic semi-automated debugging framework for equation-based modeling languages. We show how program slicing and dicing performed at the intermediate code level combined with assertion checking techniques can automate, to a large extent, the error finding process and behavior verification for physical system simulation models.

A Debugging Scheme for Declarative Equation Based Modeling Languages

This paper concerns the static analysis for debugging purposes of programs written in declarative equation based modeling languages. We first give an introduction to declarative equation based languages and the consequences equation based programming has for debugging. At the same time, we examine the particular debugging problems posed by Modelica, a declarative equation based modeling language. A brief overview of the Modelica language is also given. We also present our view of the issues and solutions based on a proposed framework for debugging declarative equation based languages. Program analysis solutions for program understanding and for static debugging of declarative equation based languages, based on bipartite graph decomposition, are presented in the paper. We also present an efficient way to annotate the underlying equations in order to help the implemented debugger to eliminate the heuristics involved in choosing the right error fixing solution. This also provides means to report the location of an error caught by the static analyzer or by the numeric solver, consistent with the users perception of the source code and simulation model.

The Social Network Classroom

Online social networking is an important part in the everyday life of college students. Despite the increasing popularity of online social networking among students and faculty members, its educational benefits are largely untested. This paper presents our experience in using social networking applications and video content distribution websites as a complement of traditional classroom education. In particular, the solution has been based on effective adaptation, extension and integration of Facebook, Twitter, Blogger YouTube and iTunes services for delivering educational material to students on mobile platforms like iPods and 3 rd generation mobile phones. The goals of the proposed educational platform, described in this paper, are to make the learning experience more engaging, to encourage collaborative work and knowledge sharing among students, and to provide an interactive platform for the educators to reach students and deliver lecture material in a totally new way.

Automated Round-trip Software Engineering in Aspect Weaving Systems

We suggest an approach to automated round-trip software engineering in source-level aspect weaving systems that allows for transparent mapping of manual edits in the woven program back to the appropriate source of origin, which is either the application core or the aspect space

Semantics guided filtering of combinatorial graph transformations in declarative equation-based languages

This paper concerns the use of static analysis for debugging purposes of declarative object-oriented equation-based modeling languages. It proposes a framework where over- and under-constraining situations present in simulation models specified in such languages are detected by combinatorial graph transformations performed on the flattened intermediate code and filtered by the semantic transformation rules derived from the original language. This is powerful enough to statically detect a broad range of errors without having to execute the simulation model. Debuggers associated with simulation environments for such languages can provide efficient error-fixing strategies based on the graph-based representation of the intermediate code. The emphasis, in this paper, is on detecting and debugging over-constraining equations, which are present in some simulation model specifications. The paper discusses various ways in which the approach is extended to allow static global analysis of the original modeling source code.