algorithms.py 文件源码

def vals2coeffs2(vals):
    """Map function values at Chebyshev points of 2nd kind to
    first-kind Chebyshev polynomial coefficients"""
    n = vals.size
    if n <= 1:
        coeffs = vals
        return coeffs
    tmp = np.append( vals[::-1], vals[1:-1] )
    if np.isreal(vals).all():
        coeffs = ifft(tmp)
        coeffs = np.real(coeffs)
    elif np.isreal( 1j*vals ).all():
        coeffs = ifft(np.imag(tmp))
        coeffs = 1j * np.real(coeffs)
    else:
        coeffs = ifft(tmp)
    coeffs = coeffs[:n]
    coeffs[1:n-1] = 2*coeffs[1:n-1]
    return coeffs