Explicit description of generalized weight modules of the algebra of polynomial integro-differential operators $I_n$.

For the algebra $I_n$ of polynomial integro-differential operators over a field $K$ of characteristic zero, a classification of simple weight and generalized weight (left and right) $I_n$-modules is given. It is proven that the category of weight $I_n$-modules is semisimple. An explicit description of generalized weight $I_n$-modules is given and using it a criterion is obtained for the problem of classification of indecomposable generalized weight $I_n$-modules to be of finite representation type, tame or wild. In the tame case, a classification of indecomposable generalized weight $I_n$-modules is given. In the wild case `natural` tame subcategories are considered with explicit description of indecomposable modules. It is proven that every generalized weight $I_n$-module is a unique sum of absolutely prime modules. For an arbitrary ring $R$, we introduce the concept of {\em absolutely prime} $R$-module (a nonzero $R$-module $M$ is absolutely prime if all nonzero subfactors of $M$ have the same annihilator). It is shown that every indecomposable generalized weight $I_n$-module is equidimensional. A criterion is given for a generalized weight $I_n$-module to be finitely generated.