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Use of linear regression and correlation matrix in the evaluation of CERES3 (Maize)
Item type: Journal Article • Journal: South African Journal of Plant and Soil • Authors: A.S. du Toit --- , South Africa J. Booysen --- , South Africa J.J. Human --- UOVS, Department of Agronomy, South AfricaA historical data set (soil water content, growth, phenology and yield) consisting of six cultivars and three planting dates was used to evaluate the CERES3 crop growth model. Linear regression and correlation matrix were used to identify algorithms in the... -
A new line search technique
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: T.A. Adewale F.M. AderibigbeIn this paper the problem of line search, an important step in most multidimensional optimization algorithms, is considered. If conjugate gradient descent is to be used in producing a descent sequence for a given functional f on a Hilbert space... -
Generalized Derivations of Associative Algebras
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Hiroaki Komatsu Atsushi NakajimaIn their paper [6], Leger and Luks introduced the notion of a generalized derivation in nonassociative algebras and got several results for generalized derivations of Lie algebras. This generalized derivation is closely related to Breˇsar's and the second author's generalized... -
(Φ, M)–extensions of near-rings
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Mark FaragIn this paper, we define and study a generalization of matrix, polynomial, and group near-rings. New results on ideal essentiality and lying over are obtained. -
Self-orthogonal codes from some Bush-type Hadamard matrices
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Dean Crnković --- Department of Mathematics, Croatia B.G. Rodrigues --- School of Mathematical Sciences, South AfricaBy means of a construction method outlined by Harada and Tonchev, we determine some non-binary self-orthogonal codes obtained from the row span of orbit matrices of Bush-type Hadamard matrices that admit a fixed-point-free and fixed-block-free automorphism of prime order. We... -
Development of fishery indicators for local management initiatives — a case study for Plettenberg Bay, South Africa
Item type: Journal Article • Journal: African Journal of Marine Science • Authors: MKS Smith CM King WHH Sauer PD CowleyIn attempts to achieve sustainability, ecosystem-based approaches to fisheries management are becoming increasingly applicable. Indicators to assess the success of management measures are an important component of this approach. Data from a recreational linefishery are used to develop and propose... -
Pairings of Sheaves of A-Modules
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Anastasios Mallios PatriceP. NtumbaIt is proved that for any free A-modules F and ε of finite rank on some C-algebraized space (X,A) a degenerate A-bilinear morphism Φ : F × ε → A induces a non-degenerate A-bilinear morphism Φ : F/ε ⊥ ×... -
Structural matrix algebras related to finite distributive lattices
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: E. Akkurt --- Gebze Institute of Technology, Turkey M. Akkurt --- Gebze Institute of Technology, Turkey G.P. Barker --- University of Missouri, Kansas City, USAIn this paper, we investigate the relation between a structural matrix algebra and the lattice properties of its lattice of invariant subspaces, and reprove known results in a fresh and an explanatory way. Moreover, we also prove the theorem which... -
Effects of the market factor on portfolio diversification: the case of market crashes
Item type: Journal Article • Journal: Investment Analysts Journal • Authors: Cheoljun Eom --- School of Business, Korea Jong Won Park --- College of Business Administration, Korea Yong H. Kim --- Carl H. Lindner College of Business, USA Taisei Kaizoji --- Graduate School of Arts and Sciences, JapanThis paper investigates empirically the effects of the market factor on the degree of portfolio diversification extracted from Markowitz's mean-variance (MV) model to explore an alternative method for improving the practical usefulness of the model. It controls for various properties... -
Putting the squeeze on the sample covariance matrix for portfolio construction
Item type: Journal Article • Journal: Investment Analysts Journal • Authors: Brian Munro --- Cadiz Asset Management, The Terraces, South Africa David Bradfield --- Department of Statistical Sciences, South AfricaPortfolio construction plays a critical role in adding performance to a fund. Central to portfolio construction are the two primary inputs: the vector of forecast returns and the covariance matrix. Our focus is on the covariance matrix. With guidance from... -
Eigenprojections and functions of a square matrix
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Christoph Hamburger --- University of Bonn, GermanyWe present polynomials for the eigenprojections or Frobenius covariants of a matrix A ∈ C n ×n . They allow for a computation of a function of A by a generalization of the Sylvester formula. -
Eelgrass beds and bare substrata – sparid and mugilid composition in contrasting littoral estuarine habitats
Item type: Journal Article • Journal: African Journal of Marine Science • Authors: M Pollard --- Department of Zoology and Entomology, South Africa AN Hodgson --- Department of Zoology and Entomology, South Africa HM Kok --- Port Elizabeth Museum, South Africa AK Whitfield --- South African Institute for Aquatic Biodiversity (SAIAB), South AfricaSeagrass beds serve as nursery grounds for many fish species and often play an important role in the juvenile stages of economically and recreationally important fishes. The eelgrass Zostera capensis is the dominant submerged macrophyte in permanently open South African... -
Avian guild assemblages in forest fragments around Budongo Forest Reserve, western Uganda
Item type: Journal Article • Journal: Ostrich: Journal of African Ornithology • Authors: Moreen Uwimbabazi --- Department of Forest Biology and Ecosystems Management, Uganda Amy E Eycott --- Institute of Biology, Norway Fred Babweteera --- Royal Zoological Society of Scotland, UK Eric Sande --- Department of Biological Sciences, Uganda Richard J Telford --- Institute of Biology, Norway Vigdis Vandvik --- Institute of Biology, NorwayRemnant forest fragments provide an opportunity for conservation in fragmented landscapes but some patches are more useful than others. Forest fragments around Budongo Forest Reserve, an Important Bird Area in western Uganda, were surveyed to explore the effects of different... -
Functionally graded metal matrix composite by centrifugal casting technique mathematical correlation
Item type: Journal Article • Journal: African Journal of Science, Technology, Innovation and Development • Authors: Williams S. Ebhota --- Discipline of Mechanical Engineering, South Africa Freddie L. Inambao --- Discipline of Mechanical Engineering, South AfricaThe functionally graded materials (FGMs) solidification process has complicated movement phenomena of fluid, solute and heat. These phenomena control the segregation of particles in a molten matrix, interactions of particles with a solidification front and the integration of particles in... -
Survival estimates for the greater crested tern Thalasseus bergii in southern Africa
Item type: Journal Article • Journal: African Journal of Marine Science • Authors: A Payo-Payo --- Group of Ecology and Animal Demography (GEDA), Spain A Sanz-Aguilar --- Group of Ecology and Animal Demography (GEDA), Spain D Gaglio --- Percy FitzPatrick Institute of African Ornithology, DST-NRF Centre of Excellence, South Africa RB Sherley --- Environment and Sustainability Institute, University of Exeter, United Kingdom TR Cook --- Percy FitzPatrick Institute of African Ornithology, DST-NRF Centre of Excellence, South Africa R Altwegg --- Statistics in Ecology, Environment and Conservation, Department of Statistical Sciences, and African Climate and Development Initiative, South Africa PG Ryan --- Percy FitzPatrick Institute of African Ornithology, DST-NRF Centre of Excellence, South AfricaThe nominate race of the greater crested tern Thalasseus bergii breeds only along the coast of the Benguela region (west coast) of southern Africa, where its population is increasing, in contrast to other species of breeding seabirds in the region... -
A novel approach for the identification of critical nodes and transmission lines for mitigating voltage instability in power networks
Item type: Journal Article • Journal: African Journal of Science, Technology, Innovation and Development • Authors: Akintunde Samson Alayande --- Department of Electrical and Electronic Engineering Science, South Africa Nnamdi Nwulu --- Department of Electrical and Electronic Engineering Science, South AfricaVoltage collapse is a major issue combating the effectiveness and optimal operation of modern power systems in recent times. This is a great threat to the security and reliability of modern power systems and, in recent times, it has been... -
Absolute matrix summability via almost increasing sequence
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Hikmet Seyhan Özarslan --- , Turkey Bagdagul Kartal --- ,In the present paper, a new theorem concerning absolute matrix summability factors, which generalizes a theorem on the summability factors of infinite series, has been proved by using almost increasing sequence and matrix transformation. -
Complex network to enhance characterization analysis in modelling product development process
Item type: Journal Article • Journal: African Journal of Science, Technology, Innovation and Development • Authors: Fateh Bencherif --- , Algeria Leila Hayet Mouss --- , AlgeriaNowadays, successful and innovative product development is highly correlated with the company's success and reason for existence. A development process is a major factor influencing cost, timing and quality of product development. It requires additional attention to decisions made about... -
The population dynamics of four grass species in relation to burning in the KwaZulu-Natal Drakensberg
Item type: Journal Article • Journal: African Journal of Range & Forage Science • Authors: Colin S Everson --- , South Africa Terry M Everson --- , South Africa Craig D Morris --- , South AfricaMarked tillers of Heteropogon contortus, Trachypogon spicatus, Tristachya leucothrix and Harpochloa falx were sampled regularly over a two-year period in Highland Sourveld burnt annually in winter and biennially in spring. Parameters recorded were height of shoot apex, tiller mass, number... -
Factor structure in Raven’s Progressive Matrices Plus in sub-Saharan Africa – Benin and Djibouti
Item type: Journal Article • Journal: Journal of Psychology in Africa • Authors: David Becker --- , Germany Gerhard Meisenberg --- , United Kingdom Edward Dutton --- , Poland Salaheldin Farah Bakhiet --- , Saudi Arabia Osman Ahmed Mohamed Humad --- , Saudi Arabia Hamissou Arouna Abdoulaye --- , Saudi Arabia Salaheldin Abdelrahman Elrasheed Seed Ahmed --- , SudanA recent meta-analysis identified factor structures in IQ-test results from non-western nations similar to those found in samples from western countries, with mostly strong loadings on a general factor. In this study, we identified the factor structure on Raven’s Standard... -
How does (C)CAPM digest anomalies?
Item type: Journal Article • Journal: Investment Analysts Journal • Authors: Qi Shi --- , ChinaIn a pioneering effort, we re-evaluate the performance of (C)CAPM (joint CAPM and consumption CAPM) in digesting a large number of anomalies. Our key contribution illustrates that the performance of (C)CAPM appears to be quite sensitive to the choice of... -
Lie triple centralizers on generalized matrix algebras
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Behrooz Fadaee --- University of Kurdistan, Iran Hoger Ghahramani --- University of Kurdistan, Iran Wu Jing --- Fayetteville State University, USAIn this article, we introduce the notion of Lie triple centralizer as follows. Let be an algebra, and be a linear mapping. We say that ϕ is a Lie triple centralizer whenever for all . Then we characterize the general... -
Further investigations on the two variables second Appell hypergeometric matrix function
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Mohamed Abdalla --- College of Science, King Khalid University, Saudi Arabia Hala Abd-Elmageed --- South Valley University, Egypt Mahmoud Abul-Ez --- Sohag University, Egypt Mohra Zayed --- College of Science, King Khalid University, Saudi ArabiaOver the last two decades, special matrix functions have become a major area of study for mathematicians and physicists. The famous four Appell hypergeometric matrix functions have received considerable attention by many authors from different points of view. The present... -
The weight distribution of hulls of binary codes from incidence matrices of complete graphs
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Khumbo Kumwenda --- Mzuzu University, Malawi Caleb Namondwe --- Mzuzu University, MalawiWe characterise the weights of all codewords of the hull of the binary code spanned by rows of an incidence matrix Bn of the complete graph Kn for n ≥ 4 and n even. Among others, we show that every... -
On a functional identity involving inverses on matrix rings
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Nadeem Ahmad Dar --- Government HSS, India Wu Jing --- Fayetteville State University, USALet be a division ring which is not a field with characteristic different from 2 and 3, and with n > 1. The purpose of this paper is to characterize additive maps f,g : satisfying the functional identity f(X) +... -
A generalization of the group inverse
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: D.E. Ferreyra --- Universidad Nacional de Río Cuarto, Argentina Saroj B. Malik --- Ambedkar University, IndiaFrom the point of view of generalizations, the core inverse of a matrix has received a lot of attention of researchers in this area resulting in many generalizations of the core inverse, like core-EP, DMP, BT, WC and so on... -
Numerical radius inequalities for the off-diagonal parts of 2 × 2 operator matrices
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Aicha Ammar --- Mustapha Stambouli University, Algeria Abdelkader Frakis --- Mustapha Stambouli University, Algeria Fuad Kittaneh --- The University of Jordan, JordanWe give some new bounds for the numerical radii of the off-diagonal parts of 2 × 2 operator matrices. A refinement of the triangle inequality for the operator norm is also given. -
On the eigenvalues of Laplacian ABC-matrix of graphs
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Bilal Ahmad Rather --- United Arab Emirates University, UAE Hilal A. Ganie --- , India Xueliang Li --- Nankai University, ChinaFor a simple graph G, the ABC-index is a degree based topological index and is defined as -
Some questions on partially ordered rings – a survey
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Jingjing Ma --- University of Houston-Clear Lake, USAThis survey provides a brief overview and new developments on some questions in the area of partially ordered and lattice-ordered rings and algebras. -
Which shrinkage is better? Portfolio selection with a cleaned random matrix
Item type: Journal Article • Journal: Investment Analysts Journal • Authors: Young C. Joo --- Shanghai University, China Sung Y. Park --- Chung-Ang University, KoreaCovariance matrix estimation is of great importance in formulating a portfolio. The sample covariance matrix, the most frequently used estimator, is well known to be unstable due to the estimation error, when the sample size is small. A shrinkage approach... -
Diversity and abundance of avifauna in the Suba Forest area, central Ethiopia
Item type: Journal Article • Journal: Ostrich: Journal of African Ornithology • Authors: Gemechis B Mosisa --- Haramaya University, Ethiopia Nega Tassie --- Bahir Dar University, Ethiopia Sintayehu W Dejene --- Haramaya University, EthiopiaBirds are one of the best-described taxa, but detailed knowledge about most bird species in Ethiopia remains rare, which hinders the development and evaluation of conservation strategies in the region. In this study, we estimated bird species diversity and abundance... -
On binary matrix properties
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Michael Hoefnagel --- Stellenbosch University, South Africa Pierre-Alain Jacqmin --- Université catholique de Louvain, Belgium Zurab Janelidze --- Stellenbosch University, South Africa Emil van der Walt --- Stellenbosch University, South AfricaThe so-called matrix properties of finitely complete categories are a special type of exactness properties that can be encoded as extended matrices of integers. The relation of entailment of matrix properties gives an interesting preorder on the set of such... -
Upper bounds for the numerical radii of powers of Hilbert space operators
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Mohammed Al-Dolat --- Jordan University of Science and Technology, Jordan Fuad Kittaneh --- The University of Jordan, JordanWe present several upper bounds for the numerical radii of 2 × 2 operator matrices. We employ these bounds to improve on some known numerical radius inequalities for powers of Hilbert space operators. In particular, we show that if T... -
On the skew eigenvalues of joined union of oriented graphs and applications
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Hilal A. Ganie --- , India Archana Ingole --- , India Ujwala Deshmukh --- , IndiaLet be an oriented graph with n vertices and m arcs having underlying graph G. The skew matrix of oriented graph , denoted by is a (−1, 0, 1)- skew symmetric matrix. The skew eigenvalues of are the eigenvalues of... -
The (B, C)-core inverse of rectangular matrices
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Huihui Zhu --- Hefei University of Technology, China Daihan Xu --- Hefei University of Technology, China Pedro Patrício --- Universidade do Minho, Portugal Dijana Mosić --- University of Niš, SerbiaLet A be an m × n complex matrix and let B, C be n × m complex matrices. The main purpose of this article is to derive several new properties of the (B, C)-core inverse. Also, we introduce and... -
Complementary bounds for the numerical and spectral radii
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Fuad Kittaneh --- The University of Jordan, Jordan Hamid Reza Moradi --- Islamic Azad University, Iran Mohammad Sababheh --- Princess Sumaya University for Technology, JordanLet denote the C* –algebra of all bounded linear operators on a Hilbert space . Among other results, we show that if are nonzero, then -
Interpolating inequalities for unitarily invariant norms and numerical radii of matrices
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Ahmad Al-Natoor --- Isra University, Jordan Omar Hirzallah --- The Hashemite University, Jordan Fuad Kittaneh --- The University of Jordan, JordanIn this paper, which is a continuation of our works in [9] and [10], we prove several interpolating inequalities for norms and numerical radii of matrices. Special cases of our results present refinements of some known inequalities. Among other results,... -
Adaptive Beta Shrinkage estimation of covariance matrices
Item type: Journal Article • Journal: Investment Analysts Journal • Authors: Henri Staal --- Department of Statistics and Actuarial Science, Stellenbosch University, South Africa Emlyn Flint --- Peresec, South AfricaAccurate estimation of the covariance matrix is essential for mean-variance portfolio optimisation, yet the sample covariance matrix is a notoriously noisy estimate, especially in high dimensions. Contemporary shrinkage methods attempt to mitigate this noise but often retain significant estimation error... -
Bounds on the spread and trace norm of the adjacency matrix of a graph
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Bilal Ahmad Rather --- Shandong University of Technology, China Hilal A. Ganie --- Government Degree College Uri, India M. Imran --- Prince Mohammad Bin Fahd University, Saudi ArabiaThe trace norm of the adjacency matrix A(G) of a graph G is the sum of absolute values of the eigenvalues of A(G) and it is well-known in the literature under the name energy (graph energy) of G. The spread... -
An efficient hybrid transform algorithm for image compression using a matrix rank-based optimization approach
Item type: Journal Article • Journal: African Journal of Science, Technology, Innovation and Development • Authors: D. Linett Sophia --- Erode Sengunthar Engineering College, India S. Kavitha --- Nandha Engineering College, IndiaThe digital images play a major part in variety of fields such medical, satellite, remote sensing, etc. Advancements in information technology have resulted in a huge number of digital images to be stored and transmitted. Since the demand for storage... -
Berezin number inequalities for 2 × 2 operator matrices and applications
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Messaoud Guesba --- El Oued University, Algeria Fuad Kittaneh --- The University of Jordan, JordanIn this paper, we present new bounds for the Berezin numbers of 2 × 2 operator matrices, which improve and generalize the existing bounds. Some other related results are also presented. -
The Frank graph
Item type: Journal Article • Journal: Quaestiones Mathematicae • Authors: Efruz Özlem Mersin --- Aksaray University, Turkey Ayşe Dilek Maden --- Selcuk University, Turkey Mustafa Bahşi --- Aksaray University, TurkeyThis paper introduces the Frank graph, a special weighted digraph with self-loops whose adjacency matrix corresponds to the Frank matrix, a special Max matrix. We derive bounds for the spectral radius and energy of the graph and illustrate these results...