给定一个普通多项式p(x)，用列向量表示，阶次从高到低排列，此函数返回p(x)的切比雪夫多项式展开的系数，返回的的结果也是一个列向量，同样按切比雪夫多项式的阶次从高到低排列



另外该函数用cos(x)项傅里叶级数展开一个多项式-

　ChebyshevExpansion.m by David Terr, Raytheon, 5-26-04



　Given a polynomial f(x) of degree n expressed as a row vector of coefficients of x^k with

　highest power on the left, expand f(x) as a sum of scalar multiples of

　Chebyshev polynomials, i.e. return the column vector of coefficients a_k with k

　running from n to 0 from top to bottom such that f(x) = sum_{k=0}^n{a_k P_k(x)}.