Stability results for Jungck-type iterative processes in convex metric spaces

In this paper, we obtain some stability results in complete convex metric spaces for nonselfmappings satisfying certain general contractivity condition. We prove our results for Jungck-Mann and Jungck-Ishikawa iterations. Our results extend several stability results in the literature.     

On the efficiency index of one-point iterative processes

In this paper, we analyze the index of efficiency of one-point iterative processes, which are in practice the most used methods to solve a nonlinear equation. We obtain the best situation for one-point iterative processes with cubic convergence: Chebyshev’s method, Halley’s method, the super-Halley method and many others classical iterative methods with order of convergence three. By means of a construction of particular multipoint iterations, we get to improve the best situation obtained for one-point methods. Moreover, these type of multipoint iterations, can be considered as quasi-one-point iterations, since they only depend on one initial approximation. Numerical examples are given and the computed results support this theory. Partly supported by the Ministry of Education and Science (MTM 2005-03091) and the University of La Rioja (ATUR-05/43).     

On convexity of hypersurfaces in the hyperbolic space

In the Hyperbolic space \({\mathbb{H}^n}\) (n ≥ 3) there are uncountably many topological types of convex hypersurfaces. When is a locally convex hypersurface in \({\mathbb{H}^n}\) globally convex, that is, when does it bound a convex set? We prove that any locally convex proper embedding of an (n ? 1)-dimensional connected manifold is the boundary of a convex set whenever the complement of (n ? 1)-flats of the resulting hypersurface is connected.     

High order iterative methods for approximating square roots

Given any natural numberm 2, we describe an iteration functiong _m (x) having the property that for any initial iterate \sqrt \alpha $$ " align="middle" border="0"> , the sequence of fixed-point iterationx _k +1 =g _m (x _k ) converges monotonically to having anm-th order rate of convergence. Form = 2 and 3,g _m (x) coincides with Newton's and Halley's iteration functions, respectively, as applied top(x) =x ² – .This research is supported in part by the National Science Foundation under Grant No. CCR-9208371.     

A new class of asynchronous iterative algorithms with order intervals

This paper deals with a new class of parallel asynchronous iterative algorithms for the solution of nonlinear systems of equations. The main feature of the new class of methods presented here is the possibility of flexible communication between processors. In particular partial updates can be exchanged. Approximation of the associated fixed point mapping is also considered. A detailed convergence study is presented. A connection with the Schwarz alternating method is made for the solution of nonlinear boundary value problems. Computational results on a shared memory multiprocessor IBM 3090 are briefly presented.

     

Convexifactors,generalized convexity and vector optimization

In this article we study a recently introduced notion of non-smooth analysis, namely convexifactors. We study some properties of the convexifactors and introduce two new chain rules. A new notion of non-smooth pseudoconvex function is introduced and its properties are studied in terms of convexifactors. We also present some optimality conditions for vector minimization in terms of convexifactors.     

On some families of multi-point iterative methods for solving nonlinear equations

Some semi-discrete analogous of well known one-point family of iterative methods for solving nonlinear scalar equations dependent on an arbitrary constant are proposed. The new families give multi-point iterative processes with the same or higher order of convergence. The convergence analysis and numerical examples are presented.     

A novel cubically convergent iterative method for computing complex roots of nonlinear equations

A fast and simple iterative method with cubic convergent is proposed for the determination of the real and complex roots of any function F(x) = 0. The idea is based upon passing a defined function G(x) tangent to F(x) at an arbitrary starting point. Choosing G(x) in the form of x^k or k^x, where k is obtained for the best correlation with the function F(x), gives an added freedom, which in contrast to all existing methods, accelerates the convergence. Also, this new method can find complex roots just by a real initial guess. This is in contrast to many other methods like the famous Newton method that needs complex initial guesses for finding complex roots. The proposed method is compared to some new and famous methods like Newton method and a modern solver that is fsolve command in MATLAB. The results show the effectiveness and robustness of this new method as compared to other methods.     

An effective iterative method for computing real and complex roots of systems of nonlinear equations

A simple and flexible iterative method is proposed to determine the real or complex roots of any system of nonlinear equations F(x)=0. The idea is based on passing defined functions G_j(x_j),j=1,…,n tangent to F_i(x_j),i,j=1,…,n at an arbitrary starting point. Choosing G_j(x_j) in the form of or or any other reversible function compatible to F_i(x_j), where k is obtained for the best correlation with the function F_i(x_j), gives an added freedom, which in contrast with all existing methods, accelerates the convergence.The method that was first proposed for computing the roots of any single function is now adopted for a system of nonlinear equations. This method is compared to some classical and famous methods such as Newton’s method and Newton-Simpson’s method. The results show the effectiveness and robustness of this new method.     

Three kinds of generalized convexity

This paper gives some properties of quasiconvex, strictly quasiconvex, and strongly quasiconvex functions. Relationships between them are discussed.This research was supported in part by the National Natural Science Foundation of China. The author would like to thank Professor M. Avriel for valuable comments about this paper.     

On the zeros of certain polynomials

We prove that certain naturally arising polynomials have all of their roots on a vertical line.     

On the Order of Convergence of a Determinantal Family of Root-Finding Methods

Recently, we have shown that for each natural number m greater than one, and each natural number k less than or equal to m, there exists a root-finding iteration function, defined as the ratio of two determinants that depend on the first m - k derivatives of the given function. For each k the corresponding matrices are upper Hessenberg matrices. Additionally, for k = 1 these matrices are Toeplitz matrices. The goal of this paper is to analyze the order of convergence of this fundamental family. Newton's method, Halley's method, and their multi-point versions are members of this family. In this paper we also derive these special cases. We prove that for fixed m, as k increases, the order of convergence decreases from m to the positive root of the characteristic polynomial of generalized Fibonacci numbers of order m. For fixed k, the order of convergence increases in m. The asymptotic error constant is also derived in terms of special determinants.     

On iterative methods for equilibrium problems

In this paper, we introduce a hybrid iterative scheme for finding a common element of the set of solutions of an equilibrium problem and the set of fixed points of finitely many nonexpansive mappings. We prove that the approximate solution converges strongly to a solution of a class of variational inequalities under some mild conditions, which is the optimality condition for some minimization problem. We also give some comments on the results of Plubtieng and Punpaeng [S. Plubtieng, R. Punpaeng, A general iterative method for equilibrium problems and fixed point problems in Hilbert spaces, J. Math. Anal. Appl. 336 (2007) 455–469]. Results obtained in this paper may be viewed as an improvement and refinement of the previously known results in this area.     

On a special class of convex functions

We answer in the affirmative to a conjecture concerning convex functions.     

Several iterative schemes for the stationary natural convection equations at different Rayleigh numbers

Several iterative schemes based on finite element discretization with triangulation for solving two‐dimensional natural convection equations are studied in this article. We establish some reference points for evaluation of the possible impact from three kinds of schemes with respect to Rayleigh numbers. In case of , all schemes are stable and convergent. Moreover, in case of , Schemes I and II can run well. Finally, in case of , only Scheme I is still stable and convergent. Numerical experiment is presented and discussed for testing of the performances of the proposed schemes, which confirms the theoretic analysis. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 31: 761–776, 2015     

On completely multiplicative functions whose values are roots of unity

Summary We prove that if a complex valued completely multiplicative function F and a positive integer ℓ≦5 satisfy the condition F(N) = U_ℓ, where U_ℓ is the set of all ℓ-th roots of unity, then {F(n+1) F(n) ∣ nε N} = U_ℓ.     

On duality for square root convex programs

Conjugate function theory is used to develop dual programs for nonseparable convex programs involving the square root function. This function arises naturally in finance when one measures the risk of a portfolio by its variance–covariance matrix, in stochastic programming under chance constraints and in location theory.