@staticmethod
def graph_implementation(arg_objs, shape, data=None):
    """Stack the expressions horizontally.

        Parameters
        ----------
        arg_objs : list
            LinExpr for each argument.
        shape : tuple
            The shape of the resulting expression.
        data :
            Additional data required by the atom.

        Returns
        -------
        tuple
            (LinOp for objective, list of constraints)
        """
    return arg_objs[0], []
