Wolfram Luther

Validated Modeling of Mechanical Systems with SmartMOBILE: Improvement of Performance by ValEncIA-IVP

Computer simulations of real life processes can generate erroneous results, in many cases due to the use of finite precision arithmetic. To ensure correctness of the results obtained with the help of a computer, various kinds of validating arithmetic and algorithms were developed. Their purpose is to provide bounds in which the exact result is guaranteed to be contained. Verified modeling of kinematics and dynamics of multibody systems is a challenging application field for such methods, largely because of possible overestimation of the guaranteed bounds, leading to meaningless results. In this paper, we discuss approaches to validated modeling of multibody systems and present a template-based tool SmartMOBILE , which features the possibility to choose an appropriate kind of arithmetic according to the modeling task. We consider different strategies for obtaining tight state enclosures in SmartMOBILE including improvements in the underlying data types (Taylor models), modeling elements (rotation error reduction), and focus on enhancement through the choice of initial value problem solvers ( ValEncIA-IVP ).

Modeling educational software for people with disabilities: theory and practice

Interactive multimedia learning systems are not suitable for people with disabilities. They tend to propose interfaces which are not accessible for learners with vision or auditory disabilities. Modeling techniques are necessary to map real world experiences to virtual worlds by using 3D auditory representations of objects for blind people and visual representations for deaf people. In this paper we describe common aspects and differences in the process of modeling the real world for applications involving tests and evaluations of cognitive tasks with people with reduced visual or auditory cues. To validate our concepts, we examine two existing systems using them as examples: AudioDoom and Whisper. AudioDoom allows blind children to explore and interact with virtual worlds created with spatial sound. Whisper implements a workplace to help people with impaired auditory abilities to recognize speech errors. The new common model considers not only the representation of the real world as proposed by the system but also the modeling of the learners knowledge about the virtual world. This can be used by the tutoring system to enable the learner to receive relevant feedback. Finally, we analyze the most important characteristics in developing systems by comparing and evaluating them and proposing some recommendations and guidelines.

Interface creation and redesign techniques in collaborative learning scenarios

User interfaces are redesigned for various purposes, like adapting interfaces or meeting new requirements during software creation processes. In the context of learning systems, the aim of interface redesign is to let the student creates his or her own interface corresponding to the abstract concept to be learned, which is reflected in the interface designed. In this article we present an approach to interface redesign in a cooperative learning scenario for cryptographic protocols. We describe an iterative workflow using two different pieces of software for the creation and redesign of interfaces and distributed simulation and evaluate this approach.

Numerical validation in current hardware architectures

From 06.01. to 11.01.2008, the Dagstuhl Seminar 08021 Numerical Validation in Current Hardware Architectures was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The rst section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.

Comparison of distance measures for historical spelling variants

This paper describes the comparison of selected distance measures in their applicability for supporting retrieval of historical spelling variants (hsv). The interdisciplinary project Rule-based search in text databases with nonstandard orthography develops a fuzzy full-text search engine for historical text documents. This engine should provide easier text access for experts as well as interested amateurs. The FlexMetric framework enhances the distance measure algorithm found to be most efficient according to the results of the evaluation. This measure can be used for multiple applications, including searching, post-ranking, transformation and even reflection about one’s own language.

Reliable Distance and Intersection Computation Using Finite Precision Geometry

In this paper we discuss reliable methods in the field of finite precision geometry. We begin with a brief survey of geometric computing and approaches generally used in dealing with accuracy and robustness problems in finite precision geometry. Moreover, two reliable geometric algorithms based on these approaches are presented. The first one is a new distance algorithm for objects modeled in a common octree. The results are exact and include good bounds on all subdivision levels. Using smoother enclosures on the highest level, a link is provided to well-known algorithms for convex and non-convex objects.

Modeling of H.264 high definition video traffic using discrete-time semi-Markov processes

Semi-Markov processes (SMPs) are widely used to model various types of data traffic in communication networks. Also, efficient and reliable analysis techniques are available. In this paper, we consider several present methods of deriving the parameters of a discrete-time semi-Markov process from given H.264 video traces in order to model the original traffic adequately. We take the distribution of frame sizes and the autocorrelation of both the original trace and the resulting SMP model into account as key quality indicators. We propose a new evolutionary optimization approach using genetic programming, which is able to significantly improve the accuracy of semi-Markov models of video traces and, at the same time, requires a smaller number of states.

Polynomial Factorization for Servers with Semi-Markovian Workload: Performance and Numerical Aspects of a Verified Solution Technique

Abstract We investigate polynomial factorization as a classical analysis method for servers with semi-Markov arrival and service processes. The modeling approach is directly applicable to queueing systems and servers in production lines and telecommunication networks, where the flexibility in adaptation to autocorrelated processes is essential. Although the method offers a compact form of the solution with favourable computation time complexity enabling to consider large state spaces and system equations of high degree, numerical stability is not guaranteed for this approach. Therefore we apply interval arithmetic in order to get verified results for the workload distributions, or otherwise to indicate that the precision of the computation has to be improved. The paper gives an overview of numerical and performance aspects of factorization in comparison to alternative methods.

Customization of user interfaces to reduce errors and enhance user acceptance

Customization is assumed to reduce error and increase user acceptance in the human-machine relation. Reconfiguration gives the operator the option to customize a user interface according to his or her own preferences. An experimental study with 72 computer science students using a simulated process control task was conducted. The reconfiguration group (RG) interactively reconfigured their user interfaces and used the reconfigured user interface in the subsequent test whereas the control group (CG) used a default user interface. Results showed significantly lower error rates and higher acceptance of the RG compared to the CG while there were no significant differences between the groups regarding situation awareness and mental workload. Reconfiguration seems to be promising and therefore warrants further exploration.

Document Management in a Computer-Integrated Classroom

This paper reports on a work in-progress scenario of a computer-integrated classroom (CiC) with a focus on document management and document sharing. Following a brief introduction on the topic of distributed (distance) and non-distributed (face-to-face) learning, the systems functionalities and architecture are being described, as well as the file structure to be found in the document archive. The system uses a unique type of XML document that can be created and edited by the FreeStyler application. The paper then concludes with a short description about the future work on the project.