code: def simple_reciprocal(x, a, b):
      
      if isinstance(x, list):
          y_l = []
          for x_v in x:
              y_l.append(a + b / x_v)
          y = np.array(y_l)
      else:
          y = a + b / x
      return y
docs: reciprocal function to fit convergence data