Coupled Vlasov and two-fluid codes on GPUs

We present a way to combine Vlasov and two-fluid codes for the simulation of a collisionless plasma in large domains while keeping full information of the velocity distribution in localized areas of interest. This is made possible by solving the full Vlasov equation in one region while the remaining area is treated by a 5-moment two-fluid code. In such a treatment, the main challenge of coupling kinetic and fluid descriptions is the interchange of physically correct boundary conditions between the different plasma models. In contrast to other treatments, we do not rely on any specific form of the distribution function, e.g. a Maxwellian type. Instead, we combine an extrapolation of the distribution function and a correction of the moments based on the fluid data. Thus, throughout the simulation both codes provide the necessary boundary conditions for each other. A speed-up factor of around 20 is achieved by using GPUs for the computationally expensive solution of the Vlasov equation and an overall factor of at least 60 using the coupling strategy combined with the GPU computation. The coupled codes were then tested on the GEM reconnection challenge

A Dynamic Interactive Decision Analysis and Support System (DIDASS). Users Guide (May 1983)

The Interactive Decision Analysis group at IIASA has recently developed an interactive decision support system called DIDASS (dynamic interactive decision analysis and support system). The major advantage of this system over most other computerized approaches to decision problems is that it is interactive, that is, it involves the decision maker in the decision process. It is an attempt to combine the analytical power of the "hard" computer model with the qualitative assessments of the decision maker. DIDASS is an interactive multicriteria programming package based on the reference (aspiration) approach to multicriteria analysis, and is capable of dealing with both linear and nonlinear problems. It has been written in FORTRAN 77, avoiding the use of any operating-system-dependent statements or commands, which means that it can be transferred to almost any computer without difficulty. This guide has been prepared for users both at IIASA and at the many collaborating institutions where DIDASS is now running, and is based on the version of DIDASS available on tape from IIASA

Spontaneous membrane formation and self-encapsulation of active rods in an inhomogeneous motility field

We study the collective dynamics of self-propelled rods in an inhomogeneous motility field. At the interface between two regions of constant but different motility, a smectic rod layer is spontaneously created through aligning interactions between the active rods, reminiscent of an artificial, semi-permeable membrane. This "active membrane" engulfes rods which are locally trapped in low-motility regions and thereby further enhances the trapping efficiency by self-organization, an effect which we call "self-encapsulation". Our results are gained by computer simulations of self-propelled rod models confined on a two-dimensional planar or spherical surface with a stepwise constant motility field, but the phenomenon should be observable in any geometry with sufficiently large spatial inhomogeneity. We also discuss possibilities to verify our predictions of active-membrane formation in experiments of self-propelled colloidal rods and vibrated granular matter

A Reference Point Approach to Nonlinear Macroeconomic Multiobjective Models

Programming-type multisectoral macroeconomic planning models are almost exclusively linear. Also, they often rely on traditional approaches such as sensitivity analysis and aggregated social welfare functions in their treatment of multiple conflicting objectives. In this paper the traditional linear programming framework is extended to handle nonlinear models and combined with an adaptive interactive decision support system to deal with multiple objectives. The decision support system is based on the reference point method. Results obtained from a simplified model of the Hungarian economy provide a numerical illustration of the approach, and an appendix containing an analysis of the shadow prices derived from the linear and nonlinear planning models is also given

OpTiX-II: A Software Environment for MCDM based on Distributed and Parallel Computing

The intention of the paper is to give an introduction to the OpTiX-II Software Environment, which supports the parallel and distributed solution of decision problems which can be represented as mathematical nonlinear programming tasks. First, a brief summary of nonsequential solution concepts for this class of decision problems on multiprocessor systems will be given. The focus of attention will be put on coarse-grained parallelization and its implementation on multi-computer clusters. The conceptual design objectives for the OpTiX-II Software Environment will be presented as well as the implementation on a workstation cluster, a transputer system and a multiprocessor workstation (shared memory). The OpTiX-II system supports the steps from the formulation of decision problems to their solution on networks of (parallel) computers. In order to demonstrate the use of OpTiX-II, the solution of a decision problem from the field of structural design is discussed and some numerical test results are supplied

A Nonlinear Dynamic Interactive Decision Analysis and Support System (DIDASS/N)

The Interactive Decision Analysis group at IIASA has developed a decision analysis and support system, called "DIDASS". Based on the Reference Point Approach for multicriteria analysis, it is an attempt to combine the analytical power of the "hard" computer model with the qualitative assessments of the decision maker. In general, DIDASS is capable of dealing with both linear and nonlinear problems. Theoretical and practical tests for solving nonlinear problems of regional water policies in open-pit mining areas have elucidated the need for an especially designed nonlinear DIDASS version. Following the presentation of the extended nonlinear version, DIDASS/N is described. DIDASS/N has been developed in collaboration between the Interactive Decision Analysis Group and the Regional Water Policies Project at IIASA. DIDASS/N has been written in FORTRAN 77. The use of operating-system-dependent statements or commands has been avoided

Identification of Bare-Airframe Dynamics from Closed-Loop Data Using Multisine Inputs and Frequency Responses

Amethod is presented for computing multiple-input multiple-output frequency responses of bare-airframe dynamics for systems excited using orthogonal phase-optimized multisines and including correlated data arising from control mixing or feedback control. The estimation was posed as the solution to an underdetermined system of linear equations, for which additional information was supplied using interpolation of the frequency responses. A simulation model of the NASA T-2 aircraft having two inputs and two outputs was used to investigate the method in the open-loop configuration and under closed-loop control. The method was also applied to flight test data from the X-56A aeroelastic demonstrator having five inputs and ten outputs and flying under closed-loop control with additional control allocation mixing. Results demonstrated that the proposed method accurately estimates the bare airframe frequency responses in the presence of correlated data from control mixing and feedback control. Results also agreed with estimates obtained using different methods that are less sensitive to correlated inputs

Qualitative Analysis of Nonlinear Systems by the Lotka-Volterra Approach

In this paper, the authors summarize recent results obtained by applying the Lotka-Volterra approach to problems in nonlinear systems analysis. This approach was developed at the Mathematics and Cybernetics Division of the GDR Academy of Sciences (Berlin); various applications have been investigated in collaboration with the System and Decision Sciences Program at IIASA. This paper should also be seen as a contribution to the debate on future directions of research at IIASA, in particular possible research into the evolution of macrosystems

Interactive Decision Analysis in Energy Planning and Policy Assessment

In recent years, there has been considerable fruitful collaboration between the System and Decision Sciences (SDS) Program and the Energy Project at IIASA. This paper gives an overview of this joint work, which involves the use of methodological tools developed in SDS to analyze decision situations based on models constructed in the Energy Project. The paper starts with a study of the use of the earliest version of DIDASS in conjunction with the energy supply model MESSAGE. It then describes how construction of more advanced energy models such as MESSAGE II, SEMA (an Austrian energy model), and GATE (a model of gas trade in Europe) took place in parallel with the development of an interactive multiple-criteria LP-solver (IMM), which represents a first step towards the integration of modeling and optimization processes in the analysis of complex decision situations. We hope that such collaboration will continue to provide a driving force for advances in different areas of IIASA research