class_docstr: Negative Volume Index (NVI)
  
  http://stockcharts.com/school/doku.php?id=chart_school:technical_indicators:negative_volume_inde
  
  Args:
      close(pandas.Series): dataset 'Close' column.
      volume(pandas.Series): dataset 'Volume' column.
      fillna(bool): if True, fill nan values with 1000.
code: def _run(self):
      price_change = self._close.pct_change()
      vol_decrease = self._volume.shift(1) > self._volume
      self._nvi = pd.Series(
          data=np.nan,
          index=self._close.index,
          dtype="float64",
          name="nvi",
      )
      self._nvi.iloc[0] = 1000
      for i in range(1, len(self._nvi)):
          if vol_decrease.iloc[i]:
              self._nvi.iloc[i] = self._nvi.iloc[i - 1] * (
                  1.0 + price_change.iloc[i]
              )
          else:
              self._nvi.iloc[i] = self._nvi.iloc[i - 1]
  
imports: import typing
  import numpy
  import pandas
  from ta.utils import IndicatorMixin, _ema
label_desc: Use image node_id 2 for calling the NegativeVolumeIndexIndicator obj's underlying member method code with example usage: obj._run() without return types