docs: def getTraitCovar(self, term_i=None):
          """
          Return the estimated trait covariance matrix for term_i (or the total if term_i is None)
              To retrieve the matrix of correlation coefficient use \see getTraitCorrCoef
  
          Args:
              term_i:     index of the random effect term we want to retrieve the covariance matrix
          Returns:
              estimated trait covariance 
          """
          assert term_i < self.n_randEffs, 'VarianceDecomposition:: specied term out of range'
  
          if term_i is None:
              RV = sp.zeros((self.P,self.P))
              for term_i in range(self.n_randEffs):
                  RV += self.getTraitCovarFun().K()
          else:
              assert term_i<self.n_randEffs, 'Term index non valid'
              RV = self.getTraitCovarFun(term_i).K()
          return RV