Homotopy fixed points for cyclic -group actions

The homotopy fixed point -compact groups for cyclic -group actions on nonabelian connected -compact groups are not homotopically discrete.

     

Convergence of paths and approximation of fixed points of asymptotically nonexpansive mappings

Let be a real Banach space with a uniformly Gâteaux differentiable norm possessing uniform normal structure, be a nonempty closed convex and bounded subset of , be an asymptotically nonexpansive mapping with sequence . Let be fixed, be such that , , and . Define the sequence iteratively by , n= 0, 1, 2, ..._. $"> It is proved that, for each integer , there is a unique such that If, in addition, and , then converges strongly to a fixed point of .

     

Following paths through turning points

The use of the continuation principle in the solution of systems of nonlinear equations frequently leads to the need to follow trajectories through turning points. This can be done by using a different parametrization at every step along the trajectory. We show how to construct accurate predictors and adaptive steplength estimators for use in predictor-corrector algorithms which follow trajectories in this way.     

Fixed points vs. coupled fixed points

In this paper, we will show some connections between fixed point and coupled fixed point problems in Banach and metric spaces.     

Characterizations of common fixed points of one-parameter nonexpansive semigroups, and convergence theorems to common fixed points

We first prove characterizations of common fixed points of one-parameter nonexpansive semigroups. We next present convergence theorems to common fixed points.     

Decomposing graphs into paths of fixed length

Barát and Thomassen have conjectured that, for any fixed tree T, there exists a natural number k _T such that the following holds: If G is a k _T -edge-connected graph such that |E(T)| divides |E(G)|, then G has a T-decomposition. The conjecture is trivial when T has one or two edges. Before submission of this paper, the conjecture had been verified only for two other trees: the paths of length 3 and 4, respectively. In this paper we verify the conjecture for each path whose length is a power of 2.     

Computational complexity of fixed points

A review of computational complexity results for approximating fixed points of Lipschitz functions is presented. Univariate and multivariate results are summarized for the second and infinity norm cases as well as the absolute, residual and relative error criteria. Contractive, nonexpansive, directionally nonexpansive, and expansive classes of functions are considered and optimal or nearly optimal algorithms exhibited. Some numerical experiments are summarized. A literature devoted to the complexity aspects of fixed point problems is listed.     

Common supports as fixed points

A family S of sets in R ^d is sundered if for each way of choosing a point from rd+1 members of S, the chosen points form the vertex-set of an (r–1)-simplex. Bisztriczky proved that for each sundered family S of d convex bodies in R ^d , and for each partition (S , S ), of S, there are exactly two hyperplanes each of which supports all the members of S and separates the members of S from the members of S . This note provides an alternate proof by obtaining each of the desired supports as (in effect) a fixed point of a continuous self-mapping of the cartesian product of the bodies.     

Iterative construction of fixed points

Abstract, It is proved that an Ishikawa—type iteration scheme converges to the fixed point of a generalized contraction map in a convex metric space. The class of generalized contraction maps includes all quasi—contraction maps. Our theorem generalizes some recent important known results     

Normality and attracting fixed points

Let k 2 be a fixed integer. We construct a non-normal familyof meromorphic functions in the unit disc with kth iteratesthat have no non-attracting fixed points in the unit disc. Wealso prove that a family of meromorphic functions in a planedomain is normal if all fixed points in the domain of the k-iteratesof all functions in the family are uniformly attracting.     

Derived subgroups of fixed points

LetA be an elementary abelianq-group acting on a finiteq′-groupG. We show that ifA has rank at least 3, then properties ofC _G(a)′, 1 ≠a ∈A restrict the structure ofG′. In particular, we consider exponent, order, rank and number of generators. This author was supported by the NSF. This author was supported by CNP_q-Brazil.     

Nilpotent residual of fixed points

Let q be a prime and A a finite q-group of exponent q acting by automorphisms on a finite \(q'\)-group G. Assume that A has order at least \(q^3\). We show that if \(\gamma _{\infty } (C_{G}(a))\) has order at most m for any \(a \in A^{\#}\), then the order of \(\gamma _{\infty } (G)\) is bounded solely in terms of m and q. If \(\gamma _{\infty } (C_{G}(a))\) has rank at most r for any \(a \in A^{\#}\), then the rank of \(\gamma _{\infty } (G)\) is bounded solely in terms of r and q.     

On fixed points of permutations

The number of fixed points of a random permutation of {1,2,…,n} has a limiting Poisson distribution. We seek a generalization, looking at other actions of the symmetric group. Restricting attention to primitive actions, a complete classification of the limiting distributions is given. For most examples, they are trivial – almost every permutation has no fixed points. For the usual action of the symmetric group on k-sets of {1,2,…,n}, the limit is a polynomial in independent Poisson variables. This exhausts all cases. We obtain asymptotic estimates in some examples, and give a survey of related results. This paper is dedicated to the life and work of our colleague Manfred Schocker. We thank Peter Cameron for his help. Diaconis was supported by NSF grant DMS-0505673. Fulman received funding from NSA grant H98230-05-1-0031 and NSF grant DMS-0503901. Guralnick was supported by NSF grant DMS-0653873. This research was facilitated by a Chaire d’Excellence grant to the University of Nice Sophia-Antipolis.