def acceleration_magnitude(ax, ay, az):
    """Cacluate the magnitude of 3D acceleration

    Args
    ----
    ax: ndarray
        x-axis acceleration values
    ay: ndarray
        y-axis acceleration values
    az: ndarray
        z-axis acceleration values

    Returns
    -------
    acc_mag: ndarray
        Magnitude of acceleration from combined acceleration axes

    http://physics.stackexchange.com/a/41655/126878
    """
    import numpy
    return numpy.sqrt(ax ** 2 + ay ** 2 + az ** 2)
