An Inequality for Projections and Convex Functions

Resumo

We propose the conditions for a continuous function to be projection-convex, i.e. f(λp+ (1 − λ)q) ≤ λf(p) + (1 − λ)f(q) for any projections p and q and any real λ ∈ (0, 1). Also we obtain the characterization of projections commutativity and the characterization of trace in terms of equalities for non-flat functions.