algorithms.py 文件源码

def coeffmult(fc, gc):
    """Coefficient-Space multiplication of equal-length first-kind
    Chebyshev series."""
    Fc = np.append( 2.*fc[:1], (fc[1:], fc[:0:-1]) )
    Gc = np.append( 2.*gc[:1], (gc[1:], gc[:0:-1]) )
    ak = ifft( fft(Fc) * fft(Gc) )
    ak = np.append( ak[:1], ak[1:] + ak[:0:-1] ) * .25
    ak = ak[:fc.size]
    inputcfs = np.append(fc, gc)
    out = np.real(ak) if np.isreal(inputcfs).all() else ak
    return out