docs: def _right_zero_blocks(self, r):
      """Number of blocks with zeros from the right in block row `r`."""
      if not self._include_off_diagonal:
        return self._block_rows - r - 1
      elif self._upper:
        return 0
      elif self._include_diagonal:
        return self._block_rows - r - 1
      else:
        return self._block_rows - r