docs: def getWeights(self, term_i=None):
          """
          Return weights for fixed effect term term_i
  
          Args:
              term_i:     fixed effect term index
          Returns:
              weights of the spefied fixed effect term.
              The output will be a KxL matrix of weights will be returned,
              where K is F.shape[1] and L is A.shape[1] of the correspoding fixed effect term
              (L will be always 1 for single-trait analysis). 
          """
          assert self.init, 'GP not initialised'
          if term_i==None:
              if self.gp.mean.n_terms==1:
                  term_i = 0
              else:
                  print('VarianceDecomposition: Specify fixed effect term index')
          return self.gp.mean.B[term_i]