tailieunhanh - Báo cáo hóa học: " ON SOME BANACH SPACE CONSTANTS ARISING IN NONLINEAR FIXED POINT AND EIGENVALUE THEORY"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: ON SOME BANACH SPACE CONSTANTS ARISING IN NONLINEAR FIXED POINT AND EIGENVALUE THEORY | ON SOME BANACH SPACE CONSTANTS ARISING IN NONLINEAR FIXED POINT AND EIGENVALUE THEORY JURGEN APPELL NINA A. ERZAKOVA SERGIO FALCON SANTANA AND MARTIN VATH Received 8 June 2004 As is well known in any infinite-dimensional Banach space one may find fixed point free self-maps of the unit ball retractions of the unit ball onto its boundary contractions of the unit sphere and nonzero maps without positive eigenvalues and normalized eigenvectors. In this paper we give upper and lower estimates or even explicit formulas for the minimal Lipschitz constant and measure of noncompactness of such maps. 1. A folklore theorem of nonlinear analysis Given a Banach space X we denote by Br X x e X xh r the closed ball and by Sr X x e X xh r the sphere of radius r 0 in X in particular we use the shortcut B X B1 X and S X S1 X for the unit ball and sphere. All maps considered in what follows are assumed to be continuous. By v x x x we denote the radial retraction ofX 0 onto S X . One of the most important results in nonlinear analysis is Brouwer s fixed point principle which states that every map f B RN B RN has a fixed point. Interestingly this characterizes finite-dimensional Banach spaces inasmuch as in each infinite-dimensional Banach space X one may find a fixed point free self-map of B X . The existence of fixed point free self-maps is closely related to the existence of other pathological maps in infinite-dimensional Banach spaces namely retractions on balls and contractions on spheres. Recall that a set S c X is a retract of a larger set B D S if there exists a map p B S with p x x for x e S this means that one may extend the identity from S by continuity to B. Likewise a set S c X is called contractible if there exists a homotopy h 0 1 X S S joining the identity with a constant map that is such that h 0 x x and h 1 x x0 e S. We summarize with the following Theorem although this theorem seems to be known in topological nonlinear analysis we sketch a brief proof which we .

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