code: def R(self, singular_value):
          
          if self.__R is not None and singular_value == self.__R_sv:
              return self.__R
  
          elif singular_value > self.jco.ncol:
              self.__R_sv = self.jco.ncol
              return self.parcov.identity
          else:
              self.log("calc R @" + str(singular_value))
              #v1 = self.qhalfx.v[:, :singular_value]
              v1 = self.xtqx.v[:, :singular_value]
              self.__R = v1 * v1.T
              self.__R_sv = singular_value
              self.log("calc R @" + str(singular_value))
              return self.__R
docs: get resolution Matrix (V_1 * V_1^T) at a singular value
  
          Parameters
          ----------
          singular_value : int
              singular value to calc R at
  
          Returns
          -------
          R : pyemu.Matrix
              resolution matrix at singular_value