Disconjugacy of symplectic systems and positive definiteness of block tridiagonal matrices

In this paper we discuss disconjugacy of symplectic difference systems in t he relation with positive definiteness of a certain associated block tridia gonal matrix. Analogous results have been recently proved for a special for m of symplectic systems-linear Hamiltonian difference systems and Sturm-Lio uville difference equations. Finally, reciprocal systems are also discussed .