Strong convergence of iterative methods for k-strictly pseudo-contractive mappings in Hilbert spaces

In this paper, we introduce composite iterative schemes for finding fixed points of k-strictly pseudo-contractive mappings for some 0?k<1 in Hilbert spaces. Then, under certain different control conditions, we establish strong convergence theorems on the composite iterative schemes. The main theorems improve and generalize the recent corresponding results of Cho et al. [5] and Marino and Xu [9] as well as Halpern [6], Wittmann [12], Moudafi [10] and Xu [14].     

Separating families for semi-algebraic sets

A new invariantp(V) is defined for real algebraic varietiesV which measures the complexity of semi-algebraic sets inV.p(V) is the least integer such that every semi-algebraic setS ?-V can be separated from its compliment byp(V) polynomials. This is a very natural invariant to consider. Using results of Bröcker [4–8] and generalizations of Bröcker’s results found in [16,17], upper bounds forp(V) are computed. The proof is simpler than the proof of similar results in [5–9],[15–18] since the complicated local-global formula for the stability index and the various pasting techniques are not needed. Lower bounds forp(V) are also computed in some special cases, the technique here being to first study the corresponding invariantp(X, G) for a finite space of orderings (X, G) [13,14].     

A note on the Ostrowski-Schneider type inertia theorem in Euclidean Jordan algebras

In a recent paper [7], Gowda et al. extended Ostrowski-Schneider type inertia results to certain linear transformations on Euclidean Jordan algebras. In particular, they showed that In(a)=In(x) whenever a°x>0 by the min-max theorem of Hirzebruch, where the inertia of an element x in a Euclidean Jordan algebra is defined by

In(x):=(π(x),ν(x),δ(x)),     

The direct product of a hopfian group with a group with cyclic ccnter

In this paper we continue our study of hopficity begun in [1], [2], [3], [4] and [5]. LetA be hopfian and letB have a cyclic center of prime power order. We improve Theorem 4 of [2] by showing that ifB has finitely many normal subgroups which form a chain (we sayB isn-normal), thenAxB is hopfian. We then consider the case whenB is ap-group of nilpotency class 2 and show that in certain casesAxB is hopfian.     

Convergence theorem for the common solution for a finite family of ?-strongly accretive operator equations

The purpose of this paper is to study a strong convergence of multi-step iterative scheme to a common solution for a finite family of uniformly continuous ?-strongly accretive operator equations in an arbitrary Banach space. As a consequence, the strong convergence theorem for the multi-step iterative sequence to a common fixed point for finite family of ?-strongly pseudocontractive mappings is also obtained. The results presented in this paper thus improve and extend the corresponding results of Inchan [6], Kang [8] and [9] and many others.     

The Newton—Kantorovich method under mild differentiability conditions and the Ptâk error estimates

We study the Newton-Kantorovich method under mild differentiability conditions. Using Zabrejko-Nguen assumptions we extend the results obtained byZabrejko andNguen in [11]. We also derive Ptâk error estimates which compare favorably with the ones obtained previously byKeller [4],Rokne [7], andArgyros in [1].     

Stability of iterative procedures with errors for approximating common fixed points of a couple of q-contractive-like mappings in Banach spaces

Recently, Agarwal, Cho, Li and Huang [R.P. Agarwal, Y.J. Cho, J. Li, N.J. Huang, Stability of iterative procedures with errors approximating common fixed points for a couple of quasi-contractive mappings in q-uniformly smooth Banach spaces, J. Math. Anal. Appl. 272 (2002) 435-447] introduced the new iterative procedures with errors for approximating the common fixed point of a couple of quasi-contractive mappings and showed the stability of these iterative procedures with errors in Banach spaces. In this paper, we introduce a new concept of a couple of q-contractive-like mappings (q>1) in a Banach space and apply these iterative procedures with errors for approximating the common fixed point of the couple of q-contractive-like mappings. The results established in this paper improve, extend and unify the corresponding ones of Agarwal, Cho, Li and Huang [R.P. Agarwal, Y.J. Cho, J. Li, N.J. Huang, Stability of iterative procedures with errors approximating common fixed points for a couple of quasi-contractive mappings in q-uniformly smooth Banach spaces, J. Math. Anal. Appl. 272 (2002) 435-447], Chidume [C.E. Chidume, Approximation of fixed points of quasi-contractive mappings in Lp spaces, Indian J. Pure Appl. Math. 22 (1991) 273-386], Chidume and Osilike [C.E. Chidume, M.O. Osilike, Fixed points iterations for quasi-contractive maps in uniformly smooth Banach spaces, Bull. Korean Math. Soc. 30 (1993) 201-212], Liu [Q.H. Liu, On Naimpally and Singh's open questions, J. Math. Anal. Appl. 124 (1987) 157-164; Q.H. Liu, A convergence theorem of the sequence of Ishikawa iterates for quasi-contractive mappings, J. Math. Anal. Appl. 146 (1990) 301-305], Osilike [M.O. Osilike, A stable iteration procedure for quasi-contractive maps, Indian J. Pure Appl. Math. 27 (1996) 25-34; M.O. Osilike, Stability of the Ishikawa iteration method for quasi-contractive maps, Indian J. Pure Appl. Math. 28 (1997) 1251-1265] and many others in the literature.     

Eine kartesisch abgeschlossene Kategorie glatter Abbildungen zwischen beliebigen lokalkonvexen Vektoräumen

This paper is a continuation of [6], in which I identified thec ^∞-complete bornological locally convex spaces (in short: 1cs) as the right ones for infinite dimensional analysis. Here I discuss smooth mappings between arbitrary 1cs, where a mapping is called smooth iff its compositions with smooth curves are smooth. The 1^st part is mainly devoted to prove the cartesian closedness of the category of (bornological,c ^∞-complete) 1cs together with the smooth mappings between them. In the 2^nd part I discuss the bornology of function spaces and furthermore demonstrate the smoothness of the differentiation process. Finally, in the 3^rd part, I compare this concept of smoothness with several others, discussed byKeller in [5], and show it to be the weakest that fulfills the chainrule.     

Amalgamation functors and boundary properties in simple theories

This paper continues the study of generalized amalgamation properties begun in [1], [2], [3], [5] and [6]. Part of the paper provides a finer analysis of the groupoids that arise from failure of 3-uniqueness in a stable theory. We show that such groupoids must be abelian and we link the binding group of the groupoids to a certain automorphism group of the monster model, showing that the group must be abelian as well. We also study connections between n-existence and n-uniqueness properties for various “dimensions” n in the wider context of simple theories. We introduce a family of weaker existence and uniqueness properties. Many of these properties did appear in the literature before; we give a category-theoretic formulation and study them systematically. Finally, we give examples of first-order simple unstable theories showing, in particular, that there is no straightforward generalization of the groupoid construction in an unstable context.     

Scale-oblivious metric fragmentation and the nonlinear Dvoretzky theorem

We introduce a randomized iterative fragmentation procedure for finite metric spaces, which is guaranteed to result in a polynomially large subset that is D-equivalent to an ultrametric, where D ∈ (2,∞) is a prescribed target distortion. Since this procedure works for D arbitrarily close to the nonlinear Dvoretzky phase transition at distortion 2, we thus obtain a much simpler probabilistic proof of the main result of [3], answering a question from [12], and yielding the best known bounds in the nonlinear Dvoretzky theorem. Our method utilizes a sequence of random scales at which a given metric space is fragmented. As in many previous randomized arguments in embedding theory, these scales are chosen irrespective of the geometry of the metric space in question. We show that our bounds are sharp if one utilizes such a “scale-oblivious” fragmentation procedure.     

Variational iteration technique for solving nonlinear equations

In this paper, we use the variational iteration technique to suggest some new iterative methods for solving nonlinear equations f(x)=0. We also discuss the convergence criteria of these new iterative methods. Comparison with other similar methods is also given. These new methods can be considered as an alternative to the Newton method. We also give several examples to illustrate the efficiency of these methods. This technique can be used to suggest a wide class of new iterative methods for solving system of nonlinear equations.     

A note on the nucleolus

It was shown byKohlberg [1972] that the nucleolus can be obtained by solving a linear program of extremely large size (2 ⁿ ! constraints). We show here how this program can be reduced to a more tractable size (4 ⁿ constraints).     

A fast minimal residual algorithm for shifted unitary matrices

A new iterative scheme is described for the solution of large linear systems of equations with a matrix of the form A = ρU + ζI, where ρ and ζ are constants, U is a unitary matrix and I is the identity matrix. We show that for such matrices a Krylov subspace basis can be generated by recursion formulas with few terms. This leads to a minimal residual algorithm that requires little storage and makes it possible to determine each iterate with fairly little arithmetic work. This algorithm provides a model for iterative methods for non-Hermitian linear systems of equations, in a similar way to the conjugate gradient and conjugate residual algorithms. Our iterative scheme illustrates that results by Faber and Manteuffel [3,4] on the existence of conjugate gradient algorithms with short recurrence relations, and related results by Joubert and Young [13], can be extended.     

Sulle classi filtrali di algebre

Summary Generalizing results of [1], we show that if a classK of algebras is filtral (as defined byMagari [1]), then so is the class of all simple algebras in the varietyW _K generated byK, and these simple objects are precisely all subalgebras of all ultraproducts of copies of algebras inK. All algebras inW _K are semisimple and regular. We then obtain charac terizations of filtral and semifiltral classes of algebras in terms of the existence of certain types of operations in these algebras, and illustrate our results with examples, mainly from ring theory.

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L'autore era parzialmente sostenuto dal contratto GP 9152 della National Science Foundation.     

A note on iterative process for G-multi degree reduction of Bézier curves

In the paper [A. Rababah, S. Mann, Iterative process for G²-multi degree reduction of Bézier curves, Applied Mathematics and Computation 217 (2011) 8126-8133], Rababah and Mann proposed an iterative method for multi-degree reduction of Bézier curves with C¹ and G²-continuity at the endpoints. In this paper, we provide a theoretical proof for the existence of the unique solution in the first step of the iterative process, while the proof in their paper applies only in some special cases. Also, we give a complete convergence proof for the iterative method. We solve the problem by using convex quadratic optimization.     

A NEW ITERATIVE METHOD FOR FINDING COMMON SOLUTIONS OF GENERALIZED EQUILIBRIUM PROBLEM, FIXED POINT PROBLEM OF INFINITE k-STRICT PSEUDO-CONTRACTIVE MAPPINGS, AND QUASI-VARIATIONAL INCLUSION PROBLEM

In this article,we introduce a hybrid iterative scheme for finding a common element of the set of solutions for a generalized equilibrium problems,the set of common fixed point for a family of infinite...     

The minimax theorem for continuous games using an elimination procedure

This article is a follow-up to an earlier paper byMarchi [1967] in which the minimax theorem is proved for continuous games, using a generalization of a procedure of elimination of superfluous strategies, already introduced byZieba [1957].     

The theory of the nonlinear Boltzmann equation for Maxwell molecules in Fourier representation

We study the Cauchy problem for the spatially homogenem Boltzmann equation for true Maxwell molecules. Using the Fourier representation introduced by Bobylev [Bo75],we give a simplified proof of a result proved by Tanaka [Ta78].Moreover, we show by means of simple geometric properties, that Tanaka functional is an entropy decreasing functional for the Boltzmann equation for Maxwell molecules.     

Two valued measure and summability of double sequences in asymmetric context

We extend the ideas of convergence and Cauchy condition of double sequences extended by a two valued measure (called ??-statistical convergence/Cauchy condition and convergence/Cauchy condition in ??-density, studied for real numbers in our recent paper [7]) to a very general structure like an asymmetric (quasi) metric space. In this context it should be noted that the above convergence ideas naturally extend the idea of statistical convergence of double sequences studied by Móricz [15] and Mursaleen and Edely [17]. We also apply the same methods to introduce, for the first time, certain ideas of divergence of double sequences in these abstract spaces. The asymmetry (or rather, absence of symmetry) of asymmetric metric spaces not only makes the whole treatment different from the real case [7] but at the same time, like [3], shows that symmetry is not essential for any result of [7] and in certain cases to get the results, we can replace symmetry by a genuinely asymmetric condition called (AMA).     

Convergence of a hybrid algorithm for a reversible semigroup of nonlinear operators in Banach spaces

The purpose of this paper is to study hybrid iterative schemes of Halpern types for a semigroup ℑ={T(s):s∈S} of relatively nonexpansive mappings on a closed and convex subset C of a Banach space with respect to a sequence {μ_n} of asymptotically left invariant means defined on an appropriate invariant subspace of l^∞(S). We prove that given a certain sequence {α_n} in [0,1], x∈C, we can generate an iterative sequence {x_n} which converges strongly to Π_F(ℑ)x where Π_F(ℑ)x is the generalized projection from C onto the fixed point set F(ℑ). Our main result is even new for the case of a Hilbert space.