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Alternatives in Implementing Noncommutative Grobner Basis Systems
No full textAlternatives in implementing systems for computing Grobner bases in path algebras (noncommutative polynomial rings) are considered and compared. Adapted forms of the standard variations to the Buchberger's algorithm (for commutative polynomial rings) are discussed, as is a pattern matching approach that finds the divisors and common multiples among the leading terms of a set of polynomials. Results from preliminary experimentation with a prototype system are used to compare the different configurations of two variations (triple elimination and basis reduction). Eight problem instances split between two classes of problems (one over free algebras, the other over mesh algebras) are used to compare the configurations. An informal analysis suggests that order plays a larger role in determining the execution time for a problem instance that the algorithm. However, by comparing configurations for each of the admissible orders, some observations can be made about the algorithms
Independent Verification and Validation: A Missing Link in Simulation Methodology?
No full textIndependent verification and validation (IV&V) is a powerful tool that can be used to mitigate the increasing complexities associated with an ever-expanding set of modeling and simulation problems. In this paper we discuss the use of independent V&V within the modeling and simulation community. Literature reviews and conversations with experienced technical managers serve as a basis for our conjecture that (a) validation is the major focus of most modeling and simulation efforts, (b) verification plays only a secondary role, and (c) independent V&V is, for all practical purposes, being ignored. In an effort to raise the awareness of the benefits and applicability of independent V&V within the modeling and simulation community, we describe in a step-by-step fashion the application of independent V&V to one particular life cycle model of a simulation study
Effect of Elevated Mass Center on the Global Stability of a Solid Supported by Elastica Columns
No full textRecently we advocated a new stability index, the global critical load, for very elastic structures. This index is extremely useful for flexible structures under large disturbances such as earthquakes. The present note determines this index for a two-dimensional rigid solid supported by two flexible columns. Using the nonlinear elastica equations the buckling and postbuckling problem is solved by a homotopy nonlinear system solver. The present results show the bifurcation curve is quite sensitive to the elevated mass center. The global buckling load is drastically reduced although the critical buckling load of linear stability analysis is the same. An explanation is given through the study of a solid supported by one column
Reducing the Mean Time to Remove Faults Through Early Fault Detection, An Experiment in Independent Verification and Validation
No full textThis paper presents the results of a study investigating the extent to which Independent Verification and Validation (IV&V) impacts early fault detection, and consequently, the mean time to remove faults. Two separate development groups, one with an IV&V team, are tasked to produce a software system from the same set of requirements. For each development phase, fault detection and removal data are recorded. An analysis of that data reveals that the group having the IV&V contingent: (a) detected errors earlier in the software development process, and (b) on the average, required substantially less time to remove those faults
Probability-One Homotopy Algorithms for Robust Controller Analysis and Synthesis with Fixed-Structure Multipliers
No full textTo enable the development of M-K (i.e., multiplier-controller) iteration schemes that do not require (suboptimal) curve fitting, mixed structured singular value analysis tests that allow the structure of the multipliers to a priori be specified, have been developed. These tests have recently been formulated as linear matrix inequality (LMI) feasibility problems. The least conservative of these tests always results in unstable multipliers and hence requires a stable coprime factorization of the multiplier before the control synthesis phase of the M-K iteration. This paper first reviews the LMI formulations of robustness analysis. It then develops alternative formulations that directly synthesize the stable factorizations and are based on the existence of positive definite solutions to certain Riccati equations. These problems, unlike the LMI problems, are not convex. The feasibility problem is approached by posing an associated optimization problem that cannot be solved using standard descent methods. Hence, we develop probability-one homotopy algorithms to find a solution. These results easily extend to provide computationally tractable algorithms for fixed-architecture, robust control design, which appear to have some advantages over the bilinear matrix inequality (BMI) approaches resulting from extensions of the LMI framework for robustness analysis
History in the Computer Science Curriculum
No full textIFIP Working Group 9.7 (History of Computing) is charged with not only encouraging the preservation of computer artifacts, the recording of the memoirs of pioneers, and the analysis of the downstream impact of computer innovations, but also on the development of educational modules on the history of computing. This paper presents an initial report on the study of the history of computing and informatics and preliminary proposals for the inclusion of aspects of the history of computing and informatics in the curriculum of university and college students
Progress Towards a World-Wide Code of Conduct
No full textIn this paper, the work of the International Federation for Information Processing (IFIP) Task Force on Ethics is described and the recommendations presented to the General Assembly are reviewed. While a common code of ethics or conduct has not been recommended for consideration by the member societies of IFIP, a set of guidelines for the establishment and evaluation of codes has been produced and procedures for the assistance of code development have been established within IFIP. This paper proposes that the data collected by the Task Force and the proposed guidelines can be used as a tool for the study of codes of practice providing a teachable, learnable educational module in courses related to the ethics of computing and computation, and looks at the next steps in bringing ethical awareness to the IT community
Some Experiments on the Sorting by Reversals Method
No full textSorting by reversals is the problem of finding the minimum number of reversals required to sort a permutation pi. The problem is significant with respect to the study of genome rearrangements and phylogeny reconstruction. This paper presents a programming framework for performing experiments on the problem. Several conjectures concerning optimal sorting sequences are tested using this framework
Time Dependent Rate-Based Modeling for Trace Data
No full textThis paper introduces a novel technique to construct an empirical model fitting time-varying (transient) trace data. The trace is a categorical or numerical time-series. The modeling technique described in this paper first builds a Mass Evolution Graph (MEG) from the trace data. Linear regression is then used to construct a time-dependent probability mass function (pmf) for each state in the trace data
Massively Parallel Simulations with Application to Queueing Networks
No full textThis paper investigates two parallel simulation methodologies, multiple replication and parallel regenerative simulation. Problems of applying these methodologies to massively parallel simulations are identified. Two approaches (MR-PI and PR) are proposed to overcome some of these problems. The MR-PI approach, based on multiple replication simulation, uses a pilot simulation to reduce the initial transient bias by starting the simulation from a state that is representative of the steady-state conditions. The PR approach allows approximate regeneration by using substate matching for models that do no regenerate frequently. Empirical results suggest that the proposed approaches can produce very accurate results