Nonconvex retracts and computation for fixed point index in cones

Abstract

In this paper we construct two retracts in a cone by nonnegative functionals of convex and concave types, and an example is given to illustrate that the retracts are nonconvex. Then the nonconvex retracts are used to compute the fixed point index for the completely continuous operator in the domains $D_1\cap D_2$ and $D_1\cup D_2$, where $D_1$ and $D_2$ are bounded open sets in the cone. The computation for fixed point index can be applied to the existence and the more precise location of positive fixed points.