def macd_generator(dataframe_name):
    """Creates MACD values
    Args:
        dataframe_name (df): Single security dataframe containing at least an 
            'ewma_fast' column and an 'ewma_slow' column
    Returns:
        A dataframe of:
            original data passed to function,
            macd (flt): Column of values for macd
    """

    # Calculate macd values
    dataframe_name['macd'] = dataframe_name['ewma_fast'] - dataframe_name['ewma_slow']

    return dataframe_name