The algorithm used appears in the paper 'Polynomial and rational solutions of holonomic systems' by Oaku-Takayama-Tsai (2000). The method is to combine isomorphisms of Bjork and Kashiwara with the restriction algorithm.
i1 : W = QQ[x, D, WeylAlgebra=>{x=>D}] o1 = W o1 : PolynomialRing, 1 differential variables |
i2 : M = W^1/ideal(x^2*D^2) o2 = cokernel | x2D2 | 1 o2 : W-module, quotient of W |
i3 : PolyExt(M) 2 o3 = HashTable{0 => QQ } 2 1 => QQ o3 : HashTable |
The object PolyExt is a method function with options.