Computation of Bivariate Characteristic Polynomials of Finitely Generated Modules over Weyl Algebras

In this paper we generalize the classical Groebner basis technique to prove the existence and present a method of computation of a dimension polynomial in two variables associated with a finitely generated D-module, that is, a finitely generated module over a Weyl algebra. We also present corresponding algorithms and examples of computation of such polynomials and show that a bivariate dimension polynomial can contain some invariants that are not carried by the Bernstein dimension polynomial. The obtained results are applied to the isomorphism problem for $D$-modules; they have also potential applications to classification problems of differential algebraic groups.