We present a theory of the definiteness (nonnegativity and positivity) of a quadratic functional $$ F over a bounded time scale. The results are given in terms of a time scale symplectic system (S), which is a time scale linear system that generalizes and unifies the linear Hamiltonian differential system and discrete symplectic system. The novelty of this paper resides in removing the assumption of normality in the characterization of the positivity of $$ F , and in establishing equivalent conditions for the nonnegativity of $$ F without any normality assumption. To reach this goal, a new notion of generalized focal points for conjoined bases $$ (X,U) of (S) is introduced, results on the piecewise-constant kernel of $$ X are obtained, and various Picone-type identities are derived under the piecewise-constant kernel condition. The results of this paper generalize and unify recent ones in each of the discrete and continuous time setting, and constitute a keystone for further development in this theory.

Last change: July 3, 2006. (c) Roman Hilscher