In mathematics, the Chebyshev rational functions are a sequence of functions which are both rational and orthogonal. They are named after Pafnuty Chebyshev. A rational Chebyshev function of degree n is defined as:
where Tn(x) is a Chebyshev polynomial of the first kind.
Many properties can be derived from the properties of the Chebyshev polynomials of the first kind. Other properties are unique to the functions themselves.
Defining:
The orthogonality of the Chebyshev rational functions may be written:
where cn = 2 for n = 0 and cn = 1 for n ≥ 1; δnm is the Kronecker delta function.
For an arbitrary function f(x) ∈ L2
ω the orthogonality relationship can be used to expand f(x):
where