sympy/sympy — pull request #1839 by skirpichev (2013-02-25 17:57:04+00:00)
Title: Fix #3669: rsolve_hyper can't find solution for F(n) + F(n - 2) + F(n - 1)==0

This time it fails, as the characteristic equation for this recurrence relation has imaginary roots:
```
In [1]: rsolve_hyper([1,1,1], 0, n)
Out[1]:
n n
⎛ ___ ⎞ ⎛ ___ ⎞
⎜ 1 ╲╱ 3 ⋅ⅈ⎟ ⎜ 1 ╲╱ 3 ⋅ⅈ⎟
C₀⋅⎜- ─ - ───────⎟ + C₁⋅⎜- ─ + ───────⎟
⎝ 2 2 ⎠ ⎝ 2 2 ⎠

```