signal.py 文件源码

def lp_fir_type(h):
    """
    Determine if FIR filter impulse response *h* is symmetric or
    antisymmetric. Return {1, 2, 3, 4} depending on FIR filter type or
    None if the FIR filter is not linear phase.
    """
    M = len(h) - 1
    n_range = range(M + 1)
    if M % 2 == 0:
        if all([NP.isclose(h[n], h[M - n]) for n in n_range]):
            return 1
        elif all([NP.isclose(h[n], -h[M - n]) for n in n_range]):
            return 3
        else:
            return None
    else:
        if all([NP.isclose(h[n], h[M - n]) for n in n_range]):
            return 2
        elif all([NP.isclose(h[n], -h[M - n]) for n in n_range]):
            return 4
        else:
            return None
    assert False