'Returns the column matrix, F, corresponding to the equations of
motion in implicit form (form [2]), M x\' = F, where the kinematical
equations are included'

@property
def comb_implicit_rhs(self):

    if (self._comb_implicit_rhs is None):
        if (self._dyn_implicit_rhs is not None):
            kin_inter = self._kin_explicit_rhs
            dyn_inter = self._dyn_implicit_rhs
            self._comb_implicit_rhs = kin_inter.col_join(dyn_inter)
            return self._comb_implicit_rhs
        else:
            raise AttributeError('comb_implicit_mat    is    not    specified    for    equations    of    motion    in    form    [1].')
    else:
        return self._comb_implicit_rhs
