code: def add_minrmsd_to_ref(self, ref, ref_frame=0, atom_indices=None, precentered=False):
          r
          from .misc import MinRmsdFeature
          f = MinRmsdFeature(ref, ref_frame=ref_frame, atom_indices=atom_indices, topology=self.topology,
                             precentered=precentered)
          self.__add_feature(f)
docs: r"""
          Adds the minimum root-mean-square-deviation (minrmsd) with respect to a reference structure to the feature list.
  
          Parameters
          ----------
          ref:
              Reference structure for computing the minrmsd. Can be of two types:
  
                  1. :py:obj:`mdtraj.Trajectory` object
                  2. filename for mdtraj to load. In this case, only the :py:obj:`ref_frame` of that file will be used.
  
          ref_frame: integer, default=0
              Reference frame of the filename specified in :py:obj:`ref`.
              This parameter has no effect if :py:obj:`ref` is not a filename.
  
          atom_indices: array_like, default=None
              Atoms that will be used for:
  
                  1. aligning the target and reference geometries.
                  2. computing rmsd after the alignment.
              If left to None, all atoms of :py:obj:`ref` will be used.
  
          precentered: bool, default=False
              Use this boolean at your own risk to let mdtraj know that the target conformations are already
              centered at the origin, i.e., their (uniformly weighted) center of mass lies at the origin.
              This will speed up the computation of the rmsd.