Lower Band.

    Formula:
    LB = CB - BW

def lower_band(close_data, high_data, low_data, period):
    """
    Lower Band.

    Formula:
    LB = CB - BW
    """
    cb = center_band(close_data, high_data, low_data, period)
    bw = band_width(high_data, low_data, period)
    lb = cb - bw
    return lb