def compute_cumulative_total_return(df, column_price):
    """
    Cumulative return on an investment is the aggregate amount that the investment has gained or lost over time,
    independent of the amount of time involved.

    cumulative total return = (price_end - price_start) / price_start = (price_end/price_start) - 1

    :param df: dataframe (sorted in ascending time order)
    :param column_price: name of source column in dataframe with price values (adjusted for splits and dividends) to
                         compute cumulative total return
    :return: cumulative total return
    """

    # compute cumulative total return
    price_start = df[column_price][0]
    price_end = df[column_price][-1]
    cumulative_return = (price_end - price_start)/price_start
    return cumulative_return