Title: On the extremal extensions of a non-negative Jacobi operator,
Abstract: We consider minimal non-negative Jacobi operator with $p\times p-$matrix
entries. Using the technique of boundary triplets and the corresponding Weyl
functions, we describe the Friedrichs and Krein extensions of the minimal
Jacobi operator. Moreover, we parameterize the set of all non-negative
self-adjoint extensions in terms of boundary conditions.