def julday2mjd(*args):
    """ julian day to modified julian day

    Args:
        julday (int) : julian day
        hour (int) : hour, optional
        minute (int) : minute, optional
        seconds (float) : seconds, optional

    Returns:
        float : modified julian day

"""
    julday = args[0]
    mjd = julday - 2400001.0
    hms = [24, 1440, 86400]
    for i, v in enumerate(args[1:]):
        mjd += v / hms[i]
    return mjd
