'Calculate the number of extra rows needed to compute ``self``.
Must return at least ``min_extra_rows``, and the default implementation
is to just return ``min_extra_rows``.  This is overridden by
downsampled terms to ensure that the first date computed is a
recomputation date.
Parameters
all_dates : pd.DatetimeIndex
The trading sessions against which ``self`` will be computed.
start_date : pd.Timestamp
The first date for which final output is requested.
end_date : pd.Timestamp
The last date for which final output is requested.
min_extra_rows : int
The minimum number of extra rows required of ``self``, as
determined by other terms that depend on ``self``.
Returns
extra_rows : int
The number of extra rows to compute.  Must be at least
``min_extra_rows``.'

def compute_extra_rows(self, all_dates, start_date, end_date, min_extra_rows):

    return min_extra_rows
