signalproc.py 文件源码

def filter_is_stable(a):
    """
    Check if filter coefficients of IIR filter are stable.

    Parameters
    ----------
    a: list or 1darray of number
        Denominator filter coefficients a.

    Returns
    -------
    is_stable: bool
        Filter is stable or not.  
    Notes
    ----
    Filter is stable if absolute value of all  roots is smaller than 1,
    see [1]_.

    References
    ----------
    .. [1] HYRY, "SciPy 'lfilter' returns only NaNs" StackOverflow,
       http://stackoverflow.com/a/8812737/1469195
    """
    assert a[0] == 1.0, (
        "a[0] should normally be zero, did you accidentally supply b?\n"
        "a: {:s}".format(str(a)))
    # from http://stackoverflow.com/a/8812737/1469195
    return np.all(np.abs(np.roots(a))<1)