Abstract: Wong, R. and H. Li, Asymptotic expansions for second-order linear difference equations, Journal of Computational and Applied Mathematics 41 (1992) 65-94.
Formal series solutions are obtained for the difference equation
y(n +2) + a(n)y(n + 1) + b(n)y(n) = 0
where
a(
n) and
b(
n) have asymptotic expansions of the form
for large values of
n, and
b0 ≠ 0. These solutions are characterized by the roots of the characteristic equation
ρ2 +
a0ρ +
b0 = 0. Our discussion is divided into three cases, according to whether the roots are distinct, or equal and do not satisfy the auxiliary equation
a1ρ +
b1 = 0, or equal and do satisfy the auxiliary equation. The last case is further divided into three subcases, according to whether the roots of the indicia) equation
α(
α -l)
ρ2 +(
a1α +
a2)
ρ +
b2 = 0 do not differ by a nonnegative integer, or differ by a positive integer, or are equal. In all cases, the formal series solutions will be shown to be asymptotic. Our approach is based on the method of successive approximations.