Matrix orthogonal Laurent polynomials and two-point Padé approximants

This paper is concerned with double sequencesC={Cn}n=−∞/∞ of Hermitian matrices with complex entriesCn∈Ms×s) and formal Laurent seriesL0(z)=−Σk=1∞C−kzk andL∞(z)=Σk=0∞Ckz−k. Making use of a Favard-type theorem for certain sequences of matrix Laurent polynomials which was obtained previously in [1] we can establish the relation between the matrix counterpart of the so-calledT-fractions and matrix orthogonal Laurent polynomials. The connection with two-point Padé approximants to the pair (L0,L∞) is also exhibited proving that such approximants are Hermitian too. Finally, error formulas are also given.