ON A NEW POSITIVE EXTENSION PROBLEM FOR BLOCK TOEPLITZ MATRICES

We consider positive extension problems for block Toeplitz matrices wh en the specified entries form a stalactite type pattern. These problem s do not seem in general to be amenable to the classical methods (they correspond to bitangential interpolation problems in the class of Car atheodory functions of a kind usually not solvable by the classical me thods of interpolation). We solve these problems by reduction to a tan gential interpolation with symmetries in a Caratheodory class. (C) 199 8 Elsevier Science Inc.