text: # # y(1) = 30
  # mu_res =  1895.4219068468078
  # lam_res =  26.314724049505035
  
  # # y(1) = 35
  # mu_res =  2224.2521876543
  # lam_res =  22.424392662354208
  
  # y(1) = 40
  mu_res =  2523.8311119211758
  lam_res =  19.76261573148329
  
  v = - 1/3
  A = 281.6 * 1000
  
  from sympy import symbols, exp, solve
  from sympy import Symbol, init_printing, pprint
  
  t = symbols('t')
  
  temp1 = (mu_res / A) * ((1+v) ** (1 + 1/v)) * (lam_res - t)
  temp2 = exp(temp1)
  temp3 = v * exp(1 + v) * temp2
  temp4 = A * (1 + temp3)**(-1/v)
  init_printing(use_unicode=True)
  y = temp4
  y_derivative = y.diff(t)
  # 直接用算过的答案，节省时间
  # y_derivative = 16475.9049382786*(1 - 0.967130801320884*exp(-0.0201655539837452*t))**2.0*exp(-0.0201655539837452*t)
  pprint(y)
  pprint(y_derivative)