class_docstr: Preallocation strategies for rolling window over expanding data set
  
  Restrictions: major_axis can only be a DatetimeIndex for now
class_docstr_tok: ["Preallocation","strategies","for","rolling","window","over","expanding","data","set","Restrictions",":","major_axis","can","only","be","a","DatetimeIndex","for","now"]
docstr: Resizes the buffer to hold a new window with a new cap_multiple.
  If cap_multiple is None, then the old cap_multiple is used.
docstr_tok: ["Resizes","the","buffer","to","hold","a","new","window","with","a","new","cap_multiple",".","If","cap_multiple","is","None",",","then","the","old","cap_multiple","is","used","."]
code: def extend_back(self, missing_dts):
      """
      Resizes the buffer to hold a new window with a new cap_multiple.
      If cap_multiple is None, then the old cap_multiple is used.
      """
      delta = len(missing_dts)
  
      if not delta:
          raise ValueError(
              "missing_dts must be a non-empty index",
          )
  
      self._window += delta
  
      self._pos += delta
  
      self.date_buf = self.date_buf.copy()
      self.date_buf.resize(self.cap)
      self.date_buf = np.roll(self.date_buf, delta)
  
      old_vals = self.buffer.values
      shape = old_vals.shape
      nan_arr = np.empty((shape[0], delta, shape[2]))
      nan_arr.fill(np.nan)
  
      new_vals = np.column_stack(
          (
              nan_arr,
              old_vals,
              np.empty(
                  (shape[0], delta * (self.cap_multiple - 1), shape[2])
              ),
          ),
      )
  
      self.buffer = pd.Panel(
          data=new_vals,
          items=self.items,
          minor_axis=self.minor_axis,
          major_axis=np.arange(self.cap),
          dtype=self.dtype,
      )
  
      # Fill the delta with the dates we calculated.
      where = slice(self._start_index, self._start_index + delta)
      self.date_buf[where] = missing_dts
  
imports: import datetime
  from copy import deepcopy
  import numpy
  import pandas
label_desc: Use image node_id 9 for calling the RollingPanel obj's underlying member method code with example usage: obj.extend_back(missing_dts) without return types