allow adjust=False when times is provided

pandas/core/window/ewm.py

@@ -134,8 +134,10 @@ class ExponentialMovingWindow(BaseWindow):
  Provide exponentially weighted (EW) calculations.
 
  Exactly one of ``com``, ``span``, ``halflife``, or ``alpha`` must be
- provided if ``times`` is not provided. If ``times`` is provided,
+ provided if ``times`` is not provided. If ``times`` is provided and ``adjust=True``,
  ``halflife`` and one of ``com``, ``span`` or ``alpha`` may be provided.
+ If ``times`` is provided and ``adjust=False``, ``halflife`` must be the only
+ provided decay-specification parameter.
 
  Parameters
  ----------
@@ -358,8 +360,6 @@ def __init__(
  self.ignore_na = ignore_na
  self.times = times
  if self.times is not None:
- if not self.adjust:
- raise NotImplementedError("times is not supported with adjust=False.")
  times_dtype = getattr(self.times, "dtype", None)
  if not (
  is_datetime64_dtype(times_dtype)
@@ -376,6 +376,9 @@ def __init__(
  # Halflife is no longer applicable when calculating COM
  # But allow COM to still be calculated if the user passes other decay args
  if common.count_not_none(self.com, self.span, self.alpha) > 0:
+ if not self.adjust:
+ raise NotImplementedError('None of com, span, or alpha can be specified if '
+ 'times is provided and adjust=False')
  self._com = get_center_of_mass(self.com, self.span, None, self.alpha)
  else:
  self._com = 1.0