code: def _compute_y(self, tau, return_r2l2=False):
          r
          r2l2 = self._compute_r2l2(tau)
          y = 2.0 * self.nu * r2l2
          if return_r2l2:
              return (y, r2l2)
          else:
              return y
docs: r"""Covert tau to :math:`y=2\nu\sum_i(\tau_i^2/l_i^2)`.
          
          Parameters
          ----------
          tau : :py:class:`Matrix`, (`M`, `D`)
              `M` inputs with dimension `D`.
          return_r2l2 : bool, optional
              Set to True to return a tuple of (`y`, `r2l2`). Default is False
              (only return `y`).
          
          Returns
          -------
          y : :py:class:`Array`, (`M`,)
              Inner argument of function.
          r2l2 : :py:class:`Array`, (`M`,)
              Anisotropically scaled distances. Only returned if `return_r2l2` is True.