ath:`\alpha = 1 - \exp\left(-\ln(2) / halflife\right)`, for
        :math:`halflife > 0`.

        If ``times`` is specified, a timedelta convertible unit over which an
        observation decays to half its value. Only applicable to ``mean()``,
        and halflife value will not apply to the other functions.

    alpha : float, optional
        Specify smoothing factor :math:`\alpha` directly

        :math:`0 < \alpha \leq 1`.

    min_periods : int, default 0
        Minimum number of observations in window required to have a value;
        otherwise, result is ``np.nan``.

    adjust : bool, default True
        Divide by decaying adjustment factor in beginning periods to account
        for imbalance in relative weightings (viewing EWMA as a moving average).

        - When ``adjust=True`` (default), the EW function is calculated using weights
          :math:`w_i = (1 - \alpha)^i`. For example, the EW moving average of the series
          [:math:`x_0, x_1, ..., x_t`] would be:

        .. math::
            y_t = \frac{x_t + (1 - \alpha)x_{t-1} + (1 - \alpha)^2 x_{t-2} + ... + (1 -
            \alpha)^t x_0}{1 + (1 - \alpha) + (1 - \alpha)^2 + ... + (1 - \alpha)^t}

        - When ``adjust=False``, the exponentially weighted function is calculated
          recursively:

        .. math::
            \begin{split}
                y_0 &= x_0\\
                y_t &= (1 - \alpha) y_{t-1} + \alpha x_t,
            \end{split}
    ignore_na : bool, default False
        Ignore missing values when calculating weights.

        - When ``ignore_na=False`` (default), weights are based on absolute positions.
          For example, the weights of :math:`x_0` and :math:`x_2` used in calculating
          the final weighted average of [:math:`x_0`, None, :math:`x_2`] are
          :math:`(1-\alpha)^2` and :math:`1` if ``adjust=True``, and
          :math:`(1-\alpha)^2` and :math:`\alpha` if ``adjust=False``.

        - When ``ignore_na=True``, weights are based
          on relative positions. For example, the weights of :math:`x_0` and :math:`x_2`
          used in calculating the final weighted average of
          [:math:`x_0`, None, :math:`x_2`] are :math:`1-\alpha` and :math:`1` if
          ``adjust=True``, and :math:`1-\alpha` and :math:`\alpha` if ``adjust=False``.

    axis : {0, 1}, default 0
        If ``0`` or ``'index'``, calculate across the rows.

        If ``1`` or ``'columns'``, calculate across the columns.

        For `Series` this parameter is unused and defaults to 0.

    times : np.ndarray, Series, default None

        Only applicable to ``mean()``.

        Times corresponding to the observations. Must be monotonically increasing and
        ``datetime64[ns]`` dtype.

        If 1-D array like, a sequence with the same shape as the observations.

    method : str {'single', 'table'}, default 'single'
        .. versionadded:: 1.4.0

        Execute the rolling operation per single column or row (``'single'``)
        or over the entire object (``'table'``).

        This argument is only implemented when specifying ``engine='numba'``
        in the method call.

        Only applicable to ``mean()``

    Returns
    -------
    pandas.api.typing.ExponentialMovingWindow

    See Also
    --------
    rolling : Provides rolling window calculations.
    expanding : Provides expanding transformations.

    Notes
    -----
    See :ref:`Windowing Operations <window.exponentially_weighted>`
    for further usage details and examples.

    Examples
    --------
    >>> df = pd.DataFrame({'B': [0, 1, 2, np.nan, 4]})
    >>> df
         B
    0  0.0
    1  1.0
    2  2.0
    3  NaN
    4  4.0

    >>> df.ewm(com=0.5).mean()
              B
    0  0.000000
    1  0.750000
    2  1.615385
    3  1.615385
    4  3.670213
    >>> df.ewm(alpha=2 / 3).mean()
              B
    0  0.000000
    1  0.750000
    2  1.615385
    3  1.615385
    4  3.670213

    **adjust**

    >>> df.ewm(com=0.5, adjust=True).mean()
              B
    0  0.000000
    1  0.750000
    2  1.615385
    3  1.615385
    4  3.670213
    >>> df.ewm(com=0.5, adjust=False).mean()
              B
    0  0.000000
    1  0.666667
    2  1.555556
    3  1.555556
    4  3.650794

    **ignore_na**

    >>> df.ewm(com=0.5, ignore_na=True).mean()
              B
    0  0.000000
    1  0.750000
    2  1.615385
    3  1.615385
    4  3.225000
    >>> df.ewm(com=0.5, ignore_na=False).mean()
              B
    0  0.000000
    1  0.750000
    2  1.615385
    3  1.615385
    4  3.670213

    **times**

    Exponentially weighted mean with weights calculated with a timedelta ``halflife``
    relative to ``times``.

    >>> times = ['2020-01-01', '2020-01-03', '2020-01-10', '2020-01-15', '2020-01-17']
    >>> df.ewm(halflife='4 days', times=pd.DatetimeIndex(times)).mean()
              B
    0  0.000000
    1  0.585786
    2  1.523889
    3  1.523889
    4  3.233686
    )
