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