code: def _update_dPxy(self):
          
          if 'kappa' in self.freeparams:
              scipy.copyto(self.dPxy['kappa'], self.Pxy / self.kappa,
                      where=CODON_TRANSITION)
              _fill_diagonals(self.dPxy['kappa'], self._diag_indices)
          if 'omega' in self.freeparams:
              scipy.copyto(self.dPxy['omega'], self.Pxy_no_omega,
                      where=CODON_NONSYN)
              _fill_diagonals(self.dPxy['omega'], self._diag_indices)
docs: Update `dPxy`.