Search

International audience; Power flow refers to the injection of power on the lines of an electrical grid, so that all the injections at the nodes form a consistent flow within the network. Optimality, in this setting, is usually intended as the minimization of the cost of generating power. Current can either be direct or alternating: while the former yields approximate linear programming formulations, the latter yields formulations of a much more interesting sort: namely, nonconvex nonlinear programs in complex numbers. In this technical survey, we derive formulation variants and relaxations of the alternating current optimal power flow problem.

Summary The use of registrations is useful in shortening Mizar proofs [1], [2], both in terms of formalization time and article space. The proposed system of classes for complex numbers aims to facilitate proofs involving basic arithmetical operations and order checking. It seems likely that the use of self-explanatory adjectives could also improve legibility of these proofs, which would be an important achievement [3]. Additionally, some potentially useful definitions, following those defined for real numbers, are introduced.

This paper describes a research that took place in a University in Rio Grande do Sul, with the aim at verifying levels of comprehension on Complex Numbers in Engineering scholars. The choice of that specific content is justified since complex numbers are the knowledge foundation for the analysis of alternating current circuits, practiced in Engineering courses. In a specific way, this investigation sought to identify and analyze errors committed by the scholars in basic mathematical operations, as addition, subtraction, multiplication and division with complex numbers. The research had a qualitative nature, being characterized as a multiple and holistic case study, whose instrument was a mixed questionnaire and whose analysis method used was Error Analysis. It is concluded that only a few scholars understand basic concepts and are able to operate with complex numbers. That was verified mainly and almost exclusively when considering addition and subtraction operations though. Even academics who had studied complex numbers in previous courses found it difficult to solve multiplication and division operations, and most have not solved these operations. Therefore, seeking to assist engineering professors and academics, a learning object is being created with the purpose of filling these learning gaps. That material aims to provide prior knowledge for the analysis of alternating current circuits and, thus, to help qualifying the processes of teaching and learning in Engineering., Este artigo apresenta um trabalho de pesquisa que se propôs a verificar o nível de compreensão sobre números complexos em acadêmicos de Engenharia de uma Instituição de Ensino Superior do Rio Grande do Sul. Justifica-se a escolha do conteúdo matemático uma vez que números complexos configuram um conhecimento base para a análise de circuitos elétricos em corrente alternada, praticada em cursos de Engenharia. Em específico, esta investigação buscou identificar e analisar os erros cometidos pelos acadêmicos em operações de matemática básica, como adição, subtração, multiplicação e divisão com números complexos. De cunho qualitativo, a pesquisa caracteriza-se como um estudo de caso múltiplo e holístico, cujos dados, produzidos por um questionário misto, foram analisados a partir de proposições da Análise de Erros. Conclui-se que são poucos os acadêmicos que compreendem conceitos e operações básicas com números complexos, tendo sido constatado certo domínio apenas nas operações de adição e subtração. Mesmo havendo, entre os acadêmicos, participantes que estudaram números complexos no Ensino Superior, a maioria deles apresentou dificuldades ou não resolveu as operações de multiplicação e divisão. Diante disso, em busca de auxiliar acadêmicos de Engenharia e seus professores, está sendo criado um objeto de aprendizagem como recurso de apoio para recuperar as lacunas de conhecimento em números complexos. Esse material tem enfoque na análise de circuitos elétricos em corrente alternada, colaborando para qualificar os processos de ensino e de aprendizagem em Engenharia.

International audience; In its raw form, micro-Doppler radar data takes the form of a complex time-series, which can be seen as multiple realizations of a Gaussian process. As such, a complex covariance matrix constitutes a viable and synthetic representation of such data. In this paper, we introduce a neural network on Hermitian Positive Definite (HPD) matrices, that is complex-valued Symmetric Positive Definite (SPD) matrices, or complex covariance matrices. We validate this new architecture on synthetic data, comparing against previous similar methods.

This paper proposes a framework for a new quantum computation based on the Feynman's path integral. The Feynman's path integral has been studied in quantum physics, however, the computational machinery may be used in universal computations. The light path design will be done in a light geometric automaton. As examples, we will present the primality test of an integer (for the deterministic case of light particle) and the stable marriage problem (for the probabilistic case of light wave).

A common problem when analyzing models, such as mathematical modeling of a biological process, is to determine if the unknown parameters of the model can be determined from given input-output data. Identifiable models are models such that the unknown parameters can be determined to have a finite number of values given input-output data. The total number of such values over the complex numbers is called the identifiability degree of the model. Unidentifiable models are models such that the unknown parameters can have an infinite number of values given input-output data. For unidentifiable models, a set of identifiable functions of the parameters are sought so that the model can be reparametrized in terms of these functions yielding an identifiable model. In this work, we use numerical algebraic geometry to determine if a model given by polynomial or rational ordinary differential equations is identifiable or unidentifiable. For identifiable models, we present a novel approach to compute the identifiability degree. For unidentifiable models, we present a novel numerical differential algebra technique aimed at computing a set of algebraically independent identifiable functions. Several examples are used to demonstrate the new techniques.

Copyright © 2013 David G. Glynn. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited., Topology and geometry should be very closely related mathematical subjects dealing with space. However, they deal with different aspects, the first with properties preserved under deformations, and the second with more linear or rigid aspects, properties invariant under translations, rotations, or projections. The present paper shows a way to go between them in an unexpected way that uses graphs on orientable surfaces, which already have widespread applications. In this way infinitely many geometrical properties are found, starting with the most basic such as the bundle and Pappus theorems. An interesting philosophical consequence is that the most general geometry over noncommutative skewfields such as Hamilton's quaternions corresponds to planar graphs, while graphs on surfaces of higher genus are related to geometry over commutative fields such as the real or complex numbers.

n line with the latest positions of Gottlob Frege, this article puts forward the hypothesis that the cognitive bases of mathematics are geometric in nature. Starting from the geometry axioms of the Elements of Euclid, we introduce a geometric theory of proportions along the lines of the one introduced by Grassmann in Ausdehnungslehre in 1844. Assuming as axioms, the cognitive contents of the theorems of Pappus and Desargues, through their configurations, in an Euclidean plane a natural field structure can be identified that reveals the purely geometric nature of complex numbers. Reasoning based on figures is becoming a growing interdisciplinary field in logic, philosophy and cognitive sciences, and is also of considerable interest in the field of education, moreover, recently, it has been emphasized that the mutual assistance that geometry and complex numbers give is poorly pointed out in teaching and that a unitary vision of geometrical aspects and calculation can be clarifying..

An adapted orthonormal frame (f"1,f"2,f"3) on a space curve r(t), where f"1=r^'/|r^'| is the curve tangent, is rotation-minimizing if its angular velocity satisfies @w@?f"1=0, i.e., the normal-plane vectors f"2,f"3 exhibit no instantaneous rotation about f"1. The simplest space curves with rational rotation-minimizing frames (RRMF curves) form a subset of the quintic spatial Pythagorean-hodograph (PH) curves, identified by certain non-linear constraints on the curve coefficients. Such curves are useful in motion planning, swept surface constructions, computer animation, robotics, and related fields. The condition that identifies the RRMF quintics as a subset of the spatial PH quintics requires a rational expression in four quadratic polynomials u(t),v(t),p(t),q(t) and their derivatives to be reducible to an analogous expression in just two polynomials a(t),b(t). This condition has been analyzed, thus far, in the case where a(t),b(t) are also quadratic, the corresponding solutions being called Class I RRMF quintics. The present study extends these prior results to provide a complete categorization of all possible PH quintic solutions to the RRMF condition. A family of Class II RRMF quintics is thereby newly identified, that correspond to the case where a(t),b(t) are linear. Modulo scaling/rotation transformations, Class II curves have five degrees of freedom, as with the Class I curves. Although Class II curves have rational RMFs that are only of degree 6-as compared to degree 8 for Class I curves-their algebraic characterization is more involved than for the latter. Computed examples are used to illustrate the construction and properties of this new class of RRMF quintics. A novel approach for generating RRMF quintics, based on the sum-of-four-squares decomposition of positive real polynomials, is also introduced and briefly discussed.

One of the most widely-used techniques for ligand-based virtual screening is similarity searching. This study adopted the concepts of quantum mechanics to present as state-of-the-art similarity method of molecules inspired from quantum theory. The representation of molecular compounds in mathematical quantum space plays a vital role in the development of quantum-based similarity approach. One of the key concepts of quantum theory is the use of complex numbers. Hence, this study proposed three various techniques to embed and to re-represent the molecular compounds to correspond with complex numbers format. The quantum-based similarity method that developed in this study depending on complex pure Hilbert space of molecules called Standard Quantum-Based (SQB). The recall of retrieved active molecules were at top 1% and top 5%, and significant test is used to evaluate our proposed methods. The MDL drug data report (MDDR), maximum unbiased validation (MUV) and Directory of Useful Decoys (DUD) data sets were used for experiments and were represented by 2D fingerprints. Simulated virtual screening experiment show that the effectiveness of SQB method was significantly increased due to the role of representational power of molecular compounds in complex numbers forms compared to Tanimoto benchmark similarity measure.

A study of how Swedish students understand the concept of complex numbers was performed. A questionnaire was issued reflecting the student view of own perception. Obtained answers show a variety of concept images describing how students adopt the concept of complex numbers. These concept images are classified into four categories in order to clarify the learning situation. Furthermore, this study also revealed a variety of misconceptions regarding this concept, and most of the misconceptions were also possible to refer to the classification system. In addition, results from an identification test show that students have difficulties discerning the basic property of complex numbers, i.e. that any number is a complex number.

This paper presents geometrical foundation for a systematic treatment of three main (elliptic, parabolic and hyperbolic) types of analytic function theories based on the representation theory of SL(2,R) group. We describe here geometries of corresponding domains. The principal role is played by Clifford algebras of matching types. In this paper we also generalise the Fillmore-Springer-Cnops construction which describes cycles as points in the extended space. This allows to consider many algebraic and geometric invariants of cycles within the Erlangen program approach. For an easy-reading introduction see arXiv:math/0607387. An outline of the whole approach is given in arXiv:1006.2115., Comment: AMS-LaTeX, 47 p, 80 PS graphics in 19 figures; v2: minor corrections v3: a substantial revision; v4 & v5: small improvements; v6: revised sections on lengths, infinitesimal cycles, parabolic Cayley transform; v7, v8 & v9: numerous minor improvements and updates; v10: the final version published in SIGMA; v11: the reference to Schwerdtfeger's book is added

Given the success of categorical approaches to quantum theory, it is interesting to consider why the complex numbers are special from a categorical perspective. We describe natural categorical conditions under which the scalars of a monoidal †-category gain many of the features of the complex numbers. Central to our approach are †-limits, certain types of limits which are compatible with the †-functor; we explore their properties and prove an existence theorem for them. Our main theorem is that in a nontrivial monoidal †-category with finite †-limits and simple tensor unit, and in which the self-adjoint scalars satisfy a completeness condition, the scalars are valued in the complex numbers, and scalar involution is exactly complex conjugation.

Trace-orthogonality is an important property of linear space-time codes that has emerged relatively recently. In this work we propose a quite general procedure for the generation of such codes for any number of transmit antennas and uses of the channel. Simulations suggest that the use of rectangular encoding matrices, in place of square ones, could be beneficial to the coding gain. Moreover we are able to guarantee full-diversity of the proposed codes when information symbols are carved from the quadratic field Q(j). Since the components of any complex number can be approximated with arbitrary precision by rational numbers, our scheme could be used to guarantee full-diversity for any conceivable complex constellation.

A reduct of a first-order structure is another structure on the same set with perhaps fewer definable predicates. We consider reducts of the complex field which are proper (not essentially the whole field) but nontrivial in a sense to be made precise in the paper. Our main result lists seven kinds of reducts. The list is complete in the sense that every reduct is a finite cover of one of these. We also investigate when two items on our list can be the same, in a couple of natural senses.

A polynomial Pythagorean-hodograph (PH) curve r(t)=(x"1(t),...,x"n(t)) in R^n is characterized by the property that its derivative components satisfy the Pythagorean condition x"1^'^2(t)+...+x"n^'^2(t)=@s^2(t) for some polynomial @s(t), ensuring that the arc length s(t)=@!@s(t)dt is simply a polynomial in the curve parameter t. PH curves have thus far been extensively studied in R^2 and R^3, by means of the complex-number and the quaternion or Hopf map representations, and the basic theory and algorithms for their practical construction and analysis are currently well-developed. However, the case of PH curves in R^n for n>3 remains largely unexplored, due to difficulties with the characterization of Pythagorean (n+1)-tuples when n>3. Invoking recent results from number theory, we characterize the structure of PH curves in dimensions n=5 and n=9, and investigate some of their properties.

In connection with the proof of his celebrated “2.4-Theorem”, Freiman proved that if α 1 , … , α N are real numbers such that each interval [ u , u + 1 / 2 ) contains at most n of the α j mod 1, then | ∑ j = 1 N exp ( 2 π i α j ) | ⩽ 2 n − N . Freiman's result was extended by Moran and Pollington, and recently by Lev. This paper contains further extensions.

Complex numbers are an obligatory content of mathematics education. However, almost without exception, in all degrees of education their application is restricted to geometrical interpretation of the complex number and solving algebraic equations. It is well known that opportunities for mathematics teaching integration, offered by specific content topics, are not fully utilized, especially in higher degrees of education. In this paper, we will present program content that can significantly improve integration of teaching, and improve the training of future mathematics teachers. Needles to say, we can achieve the last with the introduction of a new teaching course Geometry of complex numbers , as well as with the study of the mentioned content within the existing courses in elementary mathematics found at the majority of faculties that prepare mathematics teachers.