Question

我有以下代码：

u_ini = 0.1
v_ini = 0.1
z_ini = 0.1  # 初始化三个拉格朗日乘子

q = 0

lis = list(range(2))
u = list(sp.symbols('u:{}'.format(len(lis))))
v = list(sp.symbols('v:{}'.format(len(lis))))
z = sp.symbols('z')
p = list(sp.symbols('p:{}'.format(len(lis))))

lag1 = 0
lag2 = 0
lag3 = 0

p_symbol_sum = np.sum(p)

for i in range(k):
    if i < k-1:
        lag1 += B*ts_ratio[i]*sp.log(1+g[i]*p[i]/(sgm_2+g[i]*np.sum(p[i+1:k])),2)-q*(af_eff*p[i]+Pc-eh_eff*(1-ts_ratio[i])*g[i]*p_symbol_sum)
        lag2 -= u[i] * (R_min - ts_ratio[i] * B * sp.log(1 + g[i] * p[i] / (sgm_2 + g[i] * np.sum(p[i + 1:k])),2))
    elif i == k-1:
        lag1 += B*ts_ratio[i]*sp.log(1+g[i]*p[i]/(sgm_2+g[i]*p[i]),2)-q*(af_eff*p[i]+Pc-eh_eff*(1-ts_ratio[i])*g[i]*p_symbol_sum)
        lag2 -= u[i] * (R_min - ts_ratio[i] * B * sp.log(1+g[i]*p[i]/(sgm_2+g[i]*p[i]),2))
    lag3 -= v[i] * (E_min - (1 - ts_ratio[i])*eh_eff*g[i]*p_symbol_sum) + z * (p[i] - p_max)
lag_fun = lag1 + lag2 + lag3
print("lag_fun:",lag_fun)

for i in range(k):
    lag_fun.subs([(u[i],u_ini), (v[i],v_ini), (z,z_ini), (p[i],p_ini)]).evalf()
print("lag_fun:",lag_fun)

为什么我倒数第二行的子句后表达式的值没有变化。这是程序的输出。第一行是使用subs之前的输出。第二个是使用subs之后的输出。为什么没有更改？

lag_fun: -u0*(-0.5*log(0.0410609879149758*p0/(0.0410609879149758*p1 + 0.001) + 1)/log(2) + 2) - u1*(-0.5*log(0.0123909311217172*p1/(0.0123909311217172*p1 + 0.001) + 1)/log(2) + 2) - v0*(-0.00205304939574879*p0 - 0.00205304939574879*p1 + 0.2) - v1*(-0.000619546556085859*p0 - 0.000619546556085859*p1 + 0.2) - z*(p0 - 20) - z*(p1 - 20) + 0.5*log(0.0410609879149758*p0/(0.0410609879149758*p1 + 0.001) + 1)/log(2) + 0.5*log(0.0123909311217172*p1/(0.0123909311217172*p1 + 0.001) + 1)/log(2)
lag_fun: -u0*(-0.5*log(0.0410609879149758*p0/(0.0410609879149758*p1 + 0.001) + 1)/log(2) + 2) - u1*(-0.5*log(0.0123909311217172*p1/(0.0123909311217172*p1 + 0.001) + 1)/log(2) + 2) - v0*(-0.00205304939574879*p0 - 0.00205304939574879*p1 + 0.2) - v1*(-0.000619546556085859*p0 - 0.000619546556085859*p1 + 0.2) - z*(p0 - 20) - z*(p1 - 20) + 0.5*log(0.0410609879149758*p0/(0.0410609879149758*p1 + 0.001) + 1)/log(2) + 0.5*log(0.0123909311217172*p1/(0.0123909311217172*p1 + 0.001) + 1)/log(2)

Answer 1

subs不会改变任何地方，您必须捕获结果，其原因与该循环无法更改x的原因相同：

>>> x = 0
>>> for i in range(10): x + 1
>>> x
0

所以一定是

lag_fun = lag_fun.subs(etc...)

为什么有时sympy的subs函数不能替换符号的值？

1 个答案: