Tighter, Neater, Safer C and C++

Report published in the Proceedings of the National Conference on "Education and Research in the Information Society", Plovdiv, May, 2016Constructs are presented for alternative — tighter, neater and arguably less vulnerable — expression of frequently occurring patterns in C and C++ programming. We find them useful in several ways, both in teaching and in participating in programming competitions. Working programmers can also benefit from such or similar constructs.Association for the Development of the Information Society, Institute of Mathematics and Informatics Bulgarian Academy of Sciences, Plovdiv University "Paisii Hilendarski

Spiral Walk Exposed

Report published in the Proceedings of the National Conference on "Education and Research in the Information Society", Plovdiv, May, 2015Traversing a matrix along a spiral is a popular small programming problem, but one which is often solved incorrectly, or only partially, or in an ill-structured way. To benefit teaching and learning good programming style, we considered worthy to present the construction of several solutions to this problem in an expository manner. Some related combinatorial problems are also discussed. Hopefully, the text can be useful to high and higher school teachers and students, as well as to practicing programmers.Association for the Development of the Information Society, Institute of Mathematics and Informatics Bulgarian Academy of Sciences, Plovdiv University "Paisii Hilendarski

Chiral sedimentation of extended objects in viscous media

We study theoretically the chirality of a generic rigid object's sedimentation in a fluid under gravity in the low Reynolds number regime. We represent the object as a collection of small Stokes spheres or stokeslets, and the gravitational force as a constant point force applied at an arbitrary point of the object. For a generic configuration of stokeslets and forcing point, the motion takes a simple form in the nearly free draining limit where the stokeslet radius is arbitrarily small. In this case, the internal hydrodynamic interactions between stokeslets are weak, and the object follows a helical path while rotating at a constant angular velocity $\omega$ about a fixed axis. This $\omega$ is independent of initial orientation, and thus constitutes a chiral response for the object. Even though there can be no such chiral response in the absence of hydrodynamic interactions between the stokeslets, the angular velocity obtains a fixed, nonzero limit as the stokeslet radius approaches zero. We characterize empirically how $\omega$ depends on the placement of the stokeslets, concentrating on three-stokeslet objects with the external force applied far from the stokeslets. Objects with the largest $\omega$ are aligned along the forcing direction. In this case, the limiting $\omega$ varies as the inverse square of the minimum distance between stokeslets. We illustrate the prevalence of this robust chiral motion with experiments on small macroscopic objects of arbitrary shape.Comment: 35 pages, 10 figures; Section VII.A redone and other edits made for clarity. Accepted by Phys. Rev.

3D Brownian Diffusion of Submicron-Sized Particle Clusters

We report on the translation and rotation of particle clusters made through the combination of spherical building blocks. These clusters present ideal model systems to study the motion of objects with complex shape. Because they could be separated into fractions of well-defined configurations on a sufficient scale and their overall dimensions were below 300 nm, the translational and rotational diffusion coefficients of particle duplets, triplets and tetrahedrons could be determined by a combination of polarized dynamic light scattering (DLS) and depolarized dynamic light scattering (DDLS). The use of colloidal clusters for DDLS experiments overcomes the limitation of earlier experiments on the diffusion of complex objects near surfaces because the true 3D diffusion can be studied. When the exact geometry of the complex assemblies is known, different hydrodynamic models for calculating the diffusion coefficient for objects with complex shapes could be applied. Because hydrodynamic friction must be restricted to the cluster surface the so-called shell model, in which the surface is represented as a shell of small friction elements, was most suitable to describe the dynamics. A quantitative comparison of the predictions from theoretical modeling with the results obtained by DDLS showed an excellent agreement between experiment and theory

Trees and Graphs: Simple, General, Abstract, and Efficient

Report published in the Proceedings of the National Conference on "Education and Research in the Information Society", Plovdiv, May, 2019The representations of trees and graphs in general, as known from most textbooks on data structures and algorithms or similar sources, are in various ways deficient and outdated. We offer a straightforward approach, based on the notions of set and map, which is at once abstract, general, and efficient, and thus beneficial to the theory, practice, and teaching of programming.Association for the Development of the Information Societ

The Role of the Language in Teaching Introductory Programming

Report published in the Proceedings of the National Conference on "Education and Research in the Information Society", Plovdiv, June, 2017Based on a present-day view of teaching programming, desirable features are formulated for a language suitable for teaching introductory programming. On the examples of programs solving several very simple problems, a comparative evaluation is done of the languages Java and Ruby in this respect. The significance of visualization in programming education is outlined, and a suitable solution for graphical visualization is pointed at.Association for the Development of the Information Society, Institute of Mathematics and Informatics Bulgarian Academy of Sciences, Plovdiv University "Paisii Hilendarski

Език за композиционно програмиране: Обосновка и конструкция

Бойко Бл. Банчев - Представена е обосновка и описание на език за програмиране в композиционен стил за опитни и учебни цели. Под “композиционен” имаме предвид функционален стил на програмиране, при който пресмятането е йерархия от композиции и прилагания на функции. Един от данновите типове на езика е този на геометричните фигури, които могат да бъдат получавани чрез прости правила за съотнасяне и така също образуват йерархични композиции. Езикът е силно повлиян от GeomLab, но по редица свойства се различава от него значително. Статията разглежда основните черти на езика; подробното му описание и фигурноконструктивните му възможности ще бъдат представени в съпътстваща публикация.A rationale and description of a language for exploratory and educational programming in a compositional style is presented. By ‘compositional’ a functional programming style is meant where the computation is a hierarchy of function compositions and applications. One of the datatypes of the language is that of the geometrical figures that can be obtained by simple rules of spatial correlation, thus, too, forming hierarchical compositions. The language is strongly influenced by GeomLab, but differs from it substantially in many respects. The paper discusses the main features of the language; the detailed description along with the picture construction facilities will be presented in an accompanying publication. *2000 Mathematics Subject Classification: 68N15, 68N18

Programming as Metacalculation

Report published in the Proceedings of the National Conference on "Education in the Information Society", Plovdiv, May, 2013Elements of an approach to teaching programming in school are described, based on the functional paradigm and harmonically blending programming, calculation, and algebra. We believe that it ensures a smooth introduction to programming, free of contrived concepts and constructs, and also fosters the teaching of a wider and deeper mathematics in school.Association for the Development of the Information Society, Institute of Mathematics and Informatics Bulgarian Academy of Science