如何处理 scipy minimize ValueError: no enough values to unpack (expected 4, got 3)？答案

【问题标题】：How to handle scipy minimize ValueError: not enough values to unpack (expected 4, got 3)?如何处理 scipy minimize ValueError: no enough values to unpack (expected 4, got 3)？
【发布时间】：2020-12-16 18:48:12
【问题描述】：

I am trying to minimize the following function by use of the scipy library:
from scipy.optimize import minimize

def constraint1(bet):
    a,b = bet
    return 100 - a + b

con1 = {'type': 'ineq', 'fun': constraint1}
cons = [con1]
b0, b1 = (0,100), (0,100)   
bnds = (b0, b1)

def f(bet, sign = -1, *args):
    d0, d1, p0, p1 = args
    a,b = bet
    wins0 = a * (d0-1)
    wins1 = b * (d1-1)
    loss0 = b
    loss1 = a
    log0 = np.log(bank + wins0 - loss0)
    log1 = np.log(bank + wins1 - loss1)
    
    objective = (log0 * p0 + log1 * p1)
    return sign * objective

bet = [0,0]
minimize(f, bet, args = (1,2,3,4,), method = 'trust-constr', bounds = bnds, constraints = cons)

然而，这会导致ValueError:

 d0, d1, p0, p1 = args (Think this is where the error occurs)
 ValueError: not enough values to unpack (expected 4, got 3)

尝试省略 , 使其看起来像这样 :(1,2,3,4) ，但这也不起作用。

一切都会有帮助！

【问题讨论】：

标签： python optimization scipy valueerror

【解决方案1】：

你不能minimize 函数带有可选参数。该函数必须如下所示：

fun(x, *args)

没有可选参数的位置。所以你想要做的是调用你的函数明确地提供-1作为args之一：

minimize(f, bet, args = (-1, 1, 2, 3, 4,),method = 'trust-constr',
         bounds = bnds, constraints = cons)

这是documentation的链接。

【讨论】：