docs: def _make_f_expectation(self, expr):
          """
          Calculates :math:`<F>` in eq. 12 (see Ale et al. 2013) to calculate :math:`<F>` for EACH VARIABLE combination.
  
          :param expr: an expression
          :return: a column vector. Each row correspond to an element of counter.
          :rtype: :class:`sympy.Matrix`
          """
          # compute derivatives for EACH ENTRY in COUNTER
  
          derives = sp.Matrix([derive_expr_from_counter_entry(expr, self.__species, tuple(c.n_vector))
                               for c in self.__n_counter])
  
  
  
          # Computes the factorial terms for EACH entry in COUNTER
          factorial_terms = sp.Matrix([get_one_over_n_factorial(tuple(c.n_vector)) for c in self.__n_counter])
  
          # Element wise product of the two vectors
          te_vector= derives.multiply_elementwise(factorial_terms)
  
          return te_vector