Generalized power series solutions to linear partial differential equations

Let Θ = C[e−x1 , . . . , e−xn ][∂1, . . . , ∂n] and S = C[x1, . . . , xn][[eCx1+···+Cxn ]], where C is an effective field and xN 1 · · · x N n e Cx1+···+Cxn and S are given a suitable asymptotic ordering 4. Consider the mapping L : S → Sl ; f 7→ (L1 f, . . . , Ll f ), where L1, . . . , Ll ∈ Θ . For g = (g1, . . . , gl ) ∈ Sl L = im L , it is natural to ask how to solve the system L f = g. In this paper, we will effectively characterize Sl L and show how to compute a so called distinguished right inverse L−1 : Sl L → S of L . We will also characterize the solution space of the homogeneous equation Lh = 0. c © 2007 Published by Elsevier Ltd