Implement a function that computes Chebychev polynomials using recursive formulas.
Chebychev polynomials play a central role within the kernel polynomial method [1].
[1] Weiße et al., Rev. Mod. Phys. 78, 275 (2006)
Calculate Chebyshev polynomial of order “n” of first or second kind using iterative formula. Return numpy.poly1d object.
>>> import cheb
>>> print cheb.cheb(2)
2
2 x - 1
>>> print cheb.cheb(n=3, kind=2, symbol='y')
3
8 y - 4 y