Wn,1(u,ξ)=ξ1/2Iν(uξ1/2)s=0n1As(ξ)u2s+ξIν+1(uξ1/2)s=0n2Bs(ξ)u2s+1+ξ1/2Iν(uξ1/2)O(1u2n1),