def gapup(f):
    """Determine whether or not there has been a gap up.

    Parameters
    ----------
    f : pandas.DataFrame
        Dataframe with columns ``open`` and ``close``.

    Returns
    -------
    new_column : pandas.Series (bool)
        The array containing the new feature.

    References
    ----------
    *A gap is a break between prices on a chart that occurs when the
    price of a stock makes a sharp move up or down with no trading
    occurring in between* [IP_GAP]_.

    """
    new_column = f['open'] > f['close'].shift(1)
    return new_column
