Chebychev polynomial
[Tn]=chepol(n,var)
integer : polynomial order
string : polynomial variable
polynomial in the variable var
Recursive implementation of Chebychev polynomial.
Tn=2*poly(0,var)*chepol(n-1,var)-chepol(n-2,var)
with
T0=1
and T1=poly(0,var)
.