algorithms.py 文件源码

def coeffs2vals2(coeffs):
    """Map first-kind Chebyshev polynomial coefficients to
    function values at Chebyshev points of 2nd kind"""
    n = coeffs.size
    if n <= 1:
        vals = coeffs
        return vals
    coeffs = coeffs.copy()
    coeffs[1:n-1] = .5 * coeffs[1:n-1]
    tmp = np.append( coeffs, coeffs[n-2:0:-1] )
    if np.isreal(coeffs).all():
        vals = fft(tmp)
        vals = np.real(vals)
    elif np.isreal(1j*coeffs).all():
        vals = fft(np.imag(tmp))
        vals = 1j * np.real(vals)
    else:
        vals = fft(tmp)
    vals = vals[n-1::-1]
    return vals