Operator Overloading Research Articles

Algorithm 984

A toolbox called ADiGator is described for algorithmically differentiating mathematical functions in MATLAB. ADiGator performs source transformation via operator overloading using forward mode algorithmic differentiation and produces a file that can be evaluated to obtain the derivative of the original function at a numeric value of the input. A convenient by-product of the file generation is the sparsity pattern of the derivative function. Moreover, because both the input and output to the algorithm are source codes, the algorithm may be applied recursively to generate derivatives of any order. A key component of the algorithm is its ability to statically exploit derivative sparsity at the MATLAB operation level to improve runtime performance. The algorithm is applied to four different classes of example problems and is shown to produce runtime efficient derivative code. Due to the static nature of the approach, the algorithm is well suited and intended for use with problems requiring many repeated derivative computations.

Virtual Base Class, Overloading and Overriding Design Pattern in Object Oriented Programming With C++

The objective of this research paper is to discuss prime concept of inheritance in object oriented programming. Inheritance play major role in design pattern of modern programming concept. In this research paper I explained about inheritance and reusability concepts of oops. Since object oriented concepts has been introduced in modern days technology it will be assist to creation of reusable software. Inheritance and polymorphism play vital role for code reusability. OOPs have evolved to improve the quality of the programs. I also discuss about the relationship between function overloading, operator overloading and run-time polymorphism. Key focus of this research paper is to discuss new approach of inheritance mechanism which helps to solve encapsulation issues. Through virtual base class concept we explore the relationship and setup connection between code reusability and inheritance. Paper explained virtual base class, early binding and late binding concepts using coding demonstration.

Exploring the thermal limit of GaN power devices under extreme overload conditions

The performance of normally-off Gallium-Nitride (GaN) High-Electron-Mobility-Transistors (HEMTs) under extended short circuit operation is investigated. A thermal limit is found in the aluminium metallization, where at temperatures around 600°C a protrusion of the gate metal through the Inter-Level Dielectric (ILD) may form, short-circuiting gate and source metallization and thus resulting in a permanently-off failure state. The present work shows how this particular failure mode can be induced by extreme overload operation, and presents a Finite Element (FE) model which agrees with the experimental observations and gives insights in the mechanical stress-state developing in the device. The deeper thermo-mechanical understanding of the degradation mechanism suggests directions in order to improve the device's robustness.

Velocity and Torque Limit Profile Optimization of Electric Vehicle Including Limited Overload

This paper proposes a multiobjective optimization methodology for speed and torque trajectories of a light electric vehicle (LEV) traveling on a predefined route. The procedure introduced accounts for speed constraints and various elevation profiles and involves determination of the overload operation tolerances. The proposed technique facilitates the detection of alternative tradeoffs between energy and time savings for a predefined racing circuit. The method is based on the segmentation of the itinerary and involves a two-step procedure. In a first step, speed optimization is performed by tolerating substantial overloading, while in a second step, the torque overload limits per segment are optimized as well. Simulations based on a LEV dynamic model and experiments on racing circuit illustrated significant savings for both trip duration and energy consumption with respect to the classic constant-speed control technique.

Sensitivity Analysis for Building Energy Simulation Model Calibration via Algorithmic Differentiation

High-fidelity building energy simulation models are software tools that are built on the well-established physical laws of thermal/hygric processes to model heating, cooling, lighting, ventilation, and energy use of buildings. They are highly nonlinear systems that involve a large number of subroutine calls and submodel switches during execution. To calibrate a building energy simulation model with good quality, parameter sensitivity analysis is well advocated, since it aims to identify those parameters in a specific building that hold more influence on the building thermal performance than others to facilitate shortening the lengthy cycle of model calibration procedures. Since simulation models are given in a large piece of source codes and encapsulate a series of submodels, the prevailing sensitivity analysis is mostly built within the framework of Monte Carlo simulation and statistics-based random sampling methods. It is computationally intensive. We propose to perform such analysis via a differential sensitivity analysis method that relies on the estimation of derivatives. A key technical challenge is that the high nonlinearity of the model prohibits any analytical differentiation, while numerical differentiation is too sensitive to step size and suffers from a truncation error. We, hence, propose to adopt an algorithmic differentiation method, which exploits the operator overload feature of object-oriented programs, to obtain accurate and robust numerical estimations of derivatives in an automated and computationally efficient way.

Torque and thermal characteristics analysis of a fluid damping based multi-degree-of-freedom motor

This paper presents a novel fluid damping based hybrid drive multi-degrees-of-freedom permanent magnet motor. The structure and working principle of the motor is introduced. The torque features are analyzed using both finite element method and analytical method. Based on the thermal safety and thermal stability in the practical design of this motor, the thermal characteristics with heat sources are calculated and simulated. By using FEA software to model the heating status when the motor works under rated operation and high overload current conditions, the temperature contours within the motor structure can be obtained. The fluid and modal analysis are also conducted with numerical simulation. The research results validate the reasonable structure design of this motor and can be the reference of structure optimization and performance improvement indicators for this kind of motors.

Designing expression templates with concepts

SummaryConcepts are likely to be introduced in a future C++ standard. They can be used for constraining template parameters, which enables checking requirements on template parameters sooner in the compilation process, and thus providing more intelligible error messages to the user. They can also be used in the specialization of templates, thus leading to a better control over the selection of the most appropriate version of a template for a given instantiation. This latter aspect offers new possibilities in the design of template libraries, as it enhances the specialization mechanism of templates, and set it up as a solid alternative to inheritance when static binding can replace dynamic binding. This article addresses the design of expression templates (i.e., templates that represent expressions and are usually built through operator overloading) that are useful to develop an embedded domain specific language (EDSL), and can speed up the evaluation of an expression by delaying the evaluation of intermediate operations to avoid unnecessary temporary objects. We propose to use concept‐based template specialization to parse expression templates in order to ease the design of an EDSL. This approach is a static variant of the well‐known visitor design pattern that replaces the overridden methods in the double dispatch of the original design pattern by template specializations based on concepts. An example of EDSL for linear programming developed with our solution demonstrates that a concept‐based design helps producing concise and reliable code. Copyright © 2017 John Wiley & Sons, Ltd.

POT Model of Operation Vehicle Load under Toll-by-weight Mode

The phenomenon of overload operation of Expressway vehicles is particularly serious in China recently. Research on the extreme value of the vehicle load and its development trend is an urgent problem in the design of toll-by-weight mode. On the basis of statistical analysis of a highway WIM data under toll-by-weight mode in Guangdong Province, the vehicle load according to the models of the gross vehicle weight of the statistical analysis by the extreme value analysis theory to establish the pot model, gross vehicle weight distribution in the tail of the distribution function is obtained, and scientifically predict future arbitrary reproduce that may arise during the period of vehicle load value. Results show that the high speed sections of large tonnage vehicles is not accidental, in the future may also appear more large tonnage vehicle load and to pose a serious threat to the safe operation of the bridges and roads. Finally, based on the research results, the toll-by-weight standards proposed improvement suggestions and comments. It provided a useful reference for effectively control ling overloading vehicle loads.

An approach to computing discrete adjoints for MPI-parallelized models applied to Ice Sheet System Model 4.11

Abstract. Within the framework of sea-level rise projections, there is a strong need for hindcast validation of the evolution of polar ice sheets in a way that tightly matches observational records (from radar, gravity, and altimetry observations mainly). However, the computational requirements for making hindcast reconstructions possible are severe and rely mainly on the evaluation of the adjoint state of transient ice-flow models. Here, we look at the computation of adjoints in the context of the NASA/JPL/UCI Ice Sheet System Model (ISSM), written in C++ and designed for parallel execution with MPI. We present the adaptations required in the way the software is designed and written, but also generic adaptations in the tools facilitating the adjoint computations. We concentrate on the use of operator overloading coupled with the AdjoinableMPI library to achieve the adjoint computation of the ISSM. We present a comprehensive approach to (1) carry out type changing through the ISSM, hence facilitating operator overloading, (2) bind to external solvers such as MUMPS and GSL-LU, and (3) handle MPI-based parallelism to scale the capability. We demonstrate the success of the approach by computing sensitivities of hindcast metrics such as the misfit to observed records of surface altimetry on the northeastern Greenland Ice Stream, or the misfit to observed records of surface velocities on Upernavik Glacier, central West Greenland. We also provide metrics for the scalability of the approach, and the expected performance. This approach has the potential to enable a new generation of hindcast-validated projections that make full use of the wealth of datasets currently being collected, or already collected, in Greenland and Antarctica.

Transient two-phase CFD simulation of overload operating conditions and load rejection in a prototype sized Francis turbine

An increasing shift in operating conditions of hydropower turbines towards peak load operations comes with the necessity for numerical methods to account for such operations. This requires modifications to state-of-the-art CFD simulations. In the first part of this paper a 1D hydroacoustic model to represent the pressure oscillations in the penstock was introduced and coupled with a commercial CFD solver. Based on previous studies, various changes in cavitation and turbulence modeling were done to influence the behavior of a cavitating vortex rope typically occurring at high load conditions of a Francis turbine. In the second part, mesh motion was added to this model to simulate a load rejection starting from full load conditions. It was shown that additional extensions to the 3D CFD model are compulsory to model specific operating conditions as well as transient operations. Thus, accordance with measurement data at overload operation was improved and only small deviations remained. For the load rejection the maximum overspeed was well captured and the comparison of guide vane torques with model test measurements showed a sufficient agreement. With the gained insights, occurring effects which influence the performance and the life-time can be detected and conclusions for the hydraulic design as well as the operating mode can be drawn. Upcoming studies will focus on evaluating the flow field in detail and on reducing the remaining deviations by further extending the mathematical model.

Theory-based Models of Attention in Visual Workspaces

ABSTRACTTo minimize the risk of operator distraction or overload, system designers must tailor the arrangement of display channels in a visual workspace to the operator’s attentional abilities. Toward this end, computational models that embody the theoretical principles of attention control can inform the designer’s choices and narrow the space of potential display layouts for consideration. Wickens’ SEEV model incorporates four mechanisms of attentional guidance—stimulus salience, effort, expectancy, and information value—along with a probabilistic choice mechanism to predict the steady-state distribution of attention over multiple information channels. An extension of the model also predicts the speed and probability with which participants notice critical signals in a dynamic workspace. Empirical tests in single- and multi-task supervisory monitoring environments confirm that the models predict performance well, capturing the influence of various top-down and bottom-up attentional control mechanisms. Results suggest that the models can serve as theory-motivated tools to guide and assess the design of multi-channel visual workspaces.

A Source Transformation via Operator Overloading Method for the Automatic Differentiation of Mathematical Functions in MATLAB

A source transformation via operator overloading method is presented for computing derivatives of mathematical functions defined by MATLAB computer programs. The transformed derivative code that results from the method of this article computes a sparse representation of the derivative of the function defined in the original code. As in all source transformation automatic differentiation techniques, an important feature of the method is that any flow control in the original function code is preserved in the derivative code. Furthermore, the resulting derivative code relies solely upon the native MATLAB library. The method is useful in applications where it is required to repeatedly evaluate the derivative of the original function. The approach is demonstrated on several examples and is found to be highly efficient when compared to well-known MATLAB automatic differentiation programs.

Optimized higher-order automatic differentiation for the Faddeeva function

Considerable research efforts have been directed at implementing the Faddeeva function w(z) and its derivatives with respect to z, but these did not consider the key computing issue of a possible dependence of z on some variable t. The general case is to differentiate the compound function w(z(t))=w∘z(t) with respect to t by applying the chain rule for a first order derivative, or Faà di Bruno’s formula for higher-order ones. Higher-order automatic differentiation (HOAD) is an efficient and accurate technique for derivative calculation along scientific computing codes. Although codes are available for w(z), a special symbolic HOAD is required to compute accurate higher-order derivatives for w∘z(t) in an efficient manner. A thorough evaluation is carried out considering a nontrivial case study in optics to support this assertion. Program summaryProgram title: HOAD_MathFunCatalogue identifier: AFAG_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AFAG_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: yesNo. of lines in distributed program, including test data, etc.: 4737No. of bytes in distributed program, including test data, etc.: 103450Distribution format: tar.gzProgramming language: Fortran 90.Computer: Non-specific.Operating system: Non-specific.RAM: 1 megabyteClassification: 4.12.External routines: Algorithm 680 [8], Mathematical functions (included)Nature of problem:General optimized higher-order automatic differentiation of mathematical functions. Complex refractive index as a case study.Solution method:Higher-order differentiation for the general second order ordinary equation defining the mathematical functions. Optimized operator overloading recurrence formula.Unusual features:Automatic differentiation, Quadratic complexity.Running time:1 second.

Modelling Inlet Flow In Draft Tube For Different Regimes Of Hydroturbine Operation

One of the main sources of powerful pressure pulsations in the fluid flow parts of the hydroturbine at partial load or overload operation regimes is the precessing vortex rope forming due to high residual swirl of the flow downstream the hydroturbine wheel. Numerical simulation and experiments have been performed in order to study the influence of inlet flow conditions in the draft tube on level of the flow pulsations. Numerical calculations have shown that it is possible to reproduce velocity distributions at the draft tube inlet corresponding to different operation regimes of the real hydroturbines using a combination of two blade grids – rotor and stator. Experimental verification of numerical calculations was performed using an aerodynamic test rig and method of 3-d printing for fabrication of the blade grids and draft tube model. Velocity field measurements at entrance of the draft tube conical part making use of an laser-Doppler anemometer and level of the pressure pulsations using acoustic probes have allowed to define correlation between the velocity distribution type and amplitude-frequency characteristics of the flow pulsations which generated by the precessing rope.

Capitalizing on live variables: new algorithms for efficient Hessian computation via automatic differentiation

We revisit an algorithm [called Edge Pushing (EP)] for computing Hessians using Automatic Differentiation (AD) recently proposed by Gower and Mello (Optim Methods Softw 27(2): 233–249, 2012). Here we give a new, simpler derivation for the EP algorithm based on the notion of live variables from data-flow analysis in compiler theory and redesign the algorithm with close attention to general applicability and performance. We call this algorithm Livarh and develop an extension of Livarh that incorporates preaccumulation to further reduce execution time—the resulting algorithm is called Livarhacc. We engineer robust implementations for both algorithms Livarh and Livarhacc within ADOL-C, a widely-used operator overloading based AD software tool. Rigorous complexity analyses for the algorithms are provided, and the performance of the algorithms is evaluated using a mesh optimization application and several kinds of synthetic functions as testbeds. The results show that the new algorithms outperform state-of-the-art sparse methods (based on sparsity pattern detection, coloring, compressed matrix evaluation, and recovery) in some cases by orders of magnitude. We have made our implementation available online as open-source software and it will be included in a future release of ADOL-C.

Failure Analysis of a Striking Bar

This paper describes the failure investigation of a tubular shaft that is part of a hammer drill assembly. The failure investigation was particularly challenging as the fracture surfaces were completely damaged during service subsequent to the failure process. However, careful examination of the component and its assembly revealed many clues that pointed to the root causes of failure. The basic failure mode was identified as torsional fatigue failure in combination with high bending stresses. The failure was determined to be originated on the inside diameter of the tubular shaft. The root causes were determined to be operational overload in the presence of rough machining marks on the bore surface and higher than necessary operating torque required to overcome the dry adhesive friction in the system. The preventative measures recommended were manyfold including improving surface finish on the bore diameter, reducing dry sliding friction, decreasing the overall level of dynamic loads by appropriate design changes, and adding a surface strengthening heat treatment.

Source Transformation of C++ Codes for Compatibility with Operator Overloading

In C++, new features and semantics can be added to an existing software package without sweeping code changes by introducing a user-defined type using operator overloading. This approach is used, for example, to add capabilities such as algorithmic differentiation. However, the introduction of operator overloading can cause a multitude of compilation errors. In a previous paper, we identified code constructs that cause a violation of the C++ language standard after a type change, and a tool called OO-Lint based on the Clang compiler that identifies these code constructs with lint-like messages. In this paper, we present an extension of this work that automatically transforms such problematic code constructs in order to make an existing code base compatible with a semantic augmentation through operator overloading. We applied our tool to the CFD software OpenFOAM and detected and transformed 23 instances of problematic code constructs in 160,000 lines of code. A significant amount of these root causes are included up to 425 times in other files causing a tremendous compiler error amplification. In addition, we show the significance of our work with a case study of the evolution of the ice flow modeling software ISSM, comparing a recent version which was manually type changed with a legacy version. The recent version shows no signs of problematic code constructs. In contrast, our tool detected and transformed a remarkable amount of issues in the legacy version that previously had to be manually located and fixed.

Synthesis of electric drives realizing limit operating regimes in terms of operation speed and overload capacity

A special class of machine electric drives, which have an increased range of variation of the load torque and speeds with harsh and extreme operating conditions, are considered. It is shown that expansion of these parameters without increasing the rated power of the electric drive provides a significantly improved quality of technological regimes without increasing the cost of the electric drive. The strategy of the synthesis (design) of electrotechnical complexes is formulated providing the limit characteristics and consisting of the following stages: synthesis of a generic mathematical model, determination of the limit capacity of the object of control, parameter optimization of the electrotechnical complex in order to provide the limit characteristics, selection of simplified mathematical models of an electric drive, synthesis of the structures and the control system, and the search for the phase path of motion of the electric drive–working body system realizing the extreme operating regime. A determination of the possibilities of each stage is given.

The efficiency of geophysical adjoint codes generated by automatic differentiation tools

The accuracy of numerical models that describe complex physical or chemical processes depends on the choice of model parameters. Estimating an optimal set of parameters by optimization algorithms requires knowledge of the sensitivity of the process of interest to model parameters. Typically the sensitivity computation involves differentiation of the model, which can be performed by applying algorithmic differentiation (AD) tools to the underlying numerical code. However, existing AD tools differ substantially in design, legibility and computational efficiency. In this study we show that, for geophysical data assimilation problems of varying complexity, the performance of adjoint codes generated by the existing AD tools (i) Open_AD, (ii) Tapenade, (iii) NAGWare and (iv) Transformation of Algorithms in Fortran (TAF) can be vastly different. Based on simple test problems, we evaluate the efficiency of each AD tool with respect to computational speed, accuracy of the adjoint, the efficiency of memory usage, and the capability of each AD tool to handle modern FORTRAN 90–95 elements such as structures and pointers, which are new elements that either combine groups of variables or provide aliases to memory addresses, respectively. We show that, while operator overloading tools are the only ones suitable for modern codes written in object-oriented programming languages, their computational efficiency lags behind source transformation by orders of magnitude, rendering the application of these modern tools to practical assimilation problems prohibitive. In contrast, the application of source transformation tools appears to be the most efficient choice, allowing handling even large geophysical data assimilation problems. However, they can only be applied to numerical models written in earlier generations of programming languages. Our study indicates that applying existing AD tools to realistic geophysical problems faces limitations that urgently need to be solved to allow the continuous use of AD tools for solving geophysical problems on modern computer architectures.

Experimental and Fluid Structure Interaction analysis of a morphing wind turbine rotor

Active control of blade pitch for wind turbines is known to increase efficiency, especially for part and over-load operation. An unfortunate consequence of this practice is added upfront and maintenance costs, making these schemes economically viable only in large scale applications. This study investigates a novel concept for wind turbine design, in which the blade is purposefully built of a flexible material which can passively adapt its geometry according to local wind conditions. This design concept therefore acts as a low cost, simplistic passive pitch control mechanism. Using a finite-volume fluid–structure interaction solver, the aeroelastic response of such a turbine is analyzed and compared to experimental data collected from wind tunnel tests as part of this project. The results indicate that the flexible rotor is markedly superior to a geometrically identical rigid one in terms of the size of its operational envelope as well as average and maximal torque production. Using post-processing tools, the performance improvements are attributed to passive deflection of the airfoil, which act to delay blade stall and drastically change surface pressure distribution to improve turbine performance.