A second look at overloading

We study a minimal extension of the Hindley/Milner system that supports overloading and polymorphic records. We show that the type system is sound with respect to a standard untyped compositional semantics. We also show that every typable term in this system has a principal type and give an algorithm to reconstruct that type

A second look at overloading

We study a minimal extension of the Hindley/Milner system that supports overloading and polymorphic records. We show that the type system is sound with respect to a standard untyped compositional semantics. We also show that every typable term in this system has a principal type and give an algorithm to reconstruct that type

The measurement of the influence of the adhesion loss on the dynamic load of the drive reaction rod on the roller rig

The dynamic behaviour and dynamic phenomena in traction drives of railway vehicle has been studied for decades. Generally, in these days the motivation for this research is to look for answers related with service problems, which has been risen, e.g. an overloading of mechanical components as wheelsets or an intention to improve control systems of traction drives of railway vehicles. This problematic has also motivated the research at the Faculty of Mechanical Engineering at the Czech Technical University (CTU) in Prague. Nowadays it is also usual, that the main research tool has been a simulation based on a mathematical model of a railway vehicle or its specific components, as testing on real vehicles is very demanding regarding costs. However, there is an alternative – a roller rig. At the CTU in Prague there has been modernized the second roller rig for purposes of measurement regarding the torsion dynamics research, to support PhD students for their theses and possibly to extend the education for students oriented on the railway vehicle’s design. This contribution brings results of measurements just from the problematics of torsion oscillations and dynamics. Specifically, further presented measurements are on the loss of the adhesion in the contact of the wheelset and rollers, as the substitution for the railway, its impact on the reaction rod overloading and study of the axle load influence on the transition phenomena

The C++0x "Concepts" Effort

C++0x is the working title for the revision of the ISO standard of the C++ programming language that was originally planned for release in 2009 but that was delayed to 2011. The largest language extension in C++0x was "concepts", that is, a collection of features for constraining template parameters. In September of 2008, the C++ standards committee voted the concepts extension into C++0x, but then in July of 2009, the committee voted the concepts extension back out of C++0x. This article is my account of the technical challenges and debates within the "concepts" effort in the years 2003 to 2009. To provide some background, the article also describes the design space for constrained parametric polymorphism, or what is colloquially know as constrained generics. While this article is meant to be generally accessible, the writing is aimed toward readers with background in functional programming and programming language theory. This article grew out of a lecture at the Spring School on Generic and Indexed Programming at the University of Oxford, March 2010

From ACT-ONE to Miranda, a Translation Experiment

It is now almost universally acknowledged that the data language ACT-ONE associated with the formal description technique LOTOS is inappropriate for the purpose of OSI formal description. In response to this the LOTOS restandardisation activity plans to replace ACT-ONE with a functional language. Thus, compatibility between ACT-ONE and the replacement data language becomes an issue. In response to this, we present an experimental investigation of backward compatibility between ACT-ONE and the new LOTOS data language. Specifically, we investigate translating ACT-ONE data types into the functional language Miranda. Miranda has been chosen as it is a widely used functional programming language and it is close in form to the anticipated new data language. This work serves as a ``verification of concept'' for translating ACT-ONE to the E-LOTOS data language. It identifies the bounds on embedding ACT-ONE in a functional data language. In particular, it indicates what can be translated and what cannot be translated. In addition, the paper reveals pertinent issues which can inform the E-LOTOS work. For example, which constructs are needed in E-LOTOS in order to support the class of data type specifications typically made in the LOTOS setting? We conclude with a number of specific recommendations for the E-LOTOS data language

Monte Carlo evaluation of sensitivities in computational finance

In computational finance, Monte Carlo simulation is used to compute the correct prices for financial options. More important, however, is the ability to compute the so-called "Greeks'', the first and second order derivatives of the prices with respect to input parameters such as the current asset price, interest rate and level of volatility.\ud \ud This paper discusses the three main approaches to computing Greeks: finite difference, likelihood ratio method (LRM) and pathwise sensitivity calculation. The last of these has an adjoint implementation with a computational cost which is independent of the number of first derivatives to be calculated. We explain how the practical development of adjoint codes is greatly assisted by using Algorithmic Differentiation, and in particular discuss the performance achieved by the FADBAD++ software package which is based on templates and operator overloading within C++.\ud \ud The pathwise approach is not applicable when the financial payoff function is not differentiable, and even when the payoff is differentiable, the use of scripting in real-world implementations means it can be very difficult in practice to evaluate the derivative of very complex financial products. A new idea is presented to address these limitations by combining the adjoint pathwise approach for the stochastic path evolution with LRM for the payoff evaluation

Arcturus user's guide

This document describes the Arcturus programming environment, a first realization of an advanced programming environment based on the programming language Ada. It is the first environment that supplies interactive, "statement (or declaration) at a time" execution of Ada program fragments

Expression Templates Revisited: A Performance Analysis of the Current ET Methodology

In the last decade, Expression Templates (ET) have gained a reputation as an efficient performance optimization tool for C++ codes. This reputation builds on several ET-based linear algebra frameworks focused on combining both elegant and high-performance C++ code. However, on closer examination the assumption that ETs are a performance optimization technique cannot be maintained. In this paper we demonstrate and explain the inability of current ET-based frameworks to deliver high performance for dense and sparse linear algebra operations, and introduce a new "smart" ET implementation that truly allows the combination of high performance code with the elegance and maintainability of a domain-specific language.Comment: 16 pages, 7 figure