Determining t-motives and dual t-motives in Anderson’s theory

Anderson t-modules are analogs of abelian varieties in positive characteristic. Associated to such a t-module, there are its t-motive and its dual t-motive. When dealing with these objects, several questions arise which one would like to solve algorithmically. For example, for a given t-module one would like to decide whether its t-motive is indeed finitely generated free, and determine a basis. Conversely, for a given object in the category of t-motives one would like to decide whether it is the t-motive associated to a t-module, and determine that t-module. In this article, we positively answer such questions by providing the corresponding algorithms. As it turned out, the main part of all these algorithms stems from a single algorithm in non-commutative algebra, and hence the first part of this article does not deal with Anderson’s objects at all, but with results on finitely generated modules over skew polynomial rings.