Rational matrix pseudodifferential operators

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The skewfield K(d) of rational pseudodifferential operators over a differential field K is the skewfield of fractions of the algebra of differential operators K[d]. In our previous paper we showed that any H from K(d) has a minimal fractional decomposition H=AB(-1), where A,B are elements of K[d], B is non-zero, and any common right divisor of A and B is a non-zero element of K. Moreover, any right fractional decomposition of H is obtained by multiplying A and B on the right by the same non-zero element of K[d]. In the present paper we study the ring Mₙ(K(d)) of nxn matrices over the skewfield K(d). We show that similarly, any H from Mₙ(K(d)) has a minimal fractional decomposition H=AB(-1), where A,B are elements of Mₙ(K[d]), B is non-degenerate, and any common right divisor of A and B is an invertible element of the ring Mₙ(K[d]). Moreover, any right fractional decomposition of H is obtained by multiplying A and B on the right by the same non-degenerate element of Mₙ(K [d]). We give several equivalent definitions of the minimal fractional decomposition. These results are applied to the study of maximal isotropicity property, used in the theory of Dirac structures.