code: def _calc_F_guess(self, alpha, predictions, theta, weights):
          
          num = np.sum(predictions.T * theta * weights, axis=1)
          den = np.sum((1 - alpha) * theta * weights + \
                       alpha * predictions.T * weights, axis=1)
          F_guess = num/den
          # Ensure guess is not undefined
          F_guess[den==0] = 0.5
          return F_guess
docs: Calculate an estimate of the F-measure based on the scores