英文:
Wierd behavior with raising intgers to the negative powers in python
问题
我注意到在使用np.array将整数取负幂时出现了奇怪的行为。具体来说，我正在执行以下操作：
import numpy as np
a = 10**(np.arange(-1, -8, -1))
结果出现以下错误。
ValueError: 不允许整数取负整数次幂。
这很奇怪，因为代码10**(-1)正常工作。然而，以下的解决方法（其中10是浮点数而不是整数）正常工作。
import numpy as np
a = 10.**(np.arange(-1, -8, -1))
print(a) # 打印数组([1.e-01, 1.e-02, 1.e-03, 1.e-04, 1.e-05, 1.e-06, 1.e-07])
为什么对整数不有效？欢迎任何解释。
英文:
I am observing this weird behavior when I am raising an integer to the negative power using an np.array. Specifically, I am doing
import numpy as np
a = 10**(np.arange(-1, -8, -1))
and it results in the following error.
>ValueError: Integers to negative integer powers are not allowed.
This is strange as the code 10**(-1) works fine. However the following workaround (where 10 is a float instead of integer) works fine.
import numpy as np
a = 10.**(np.arange(-1, -8, -1)
print(a) # Prints array([1.e-01, 1.e-02, 1.e-03, 1.e-04, 1.e-05, 1.e-06, 1.e-07])
Why is it not valid for integers? Any explanation is appreciated.
答案1
得分: 2
这是因为输入的10是一个整数。
10**(np.arange(-1, -8, -1))
numpy.arange()被设计成必须要给出整数或什么都不给出，因为输入是整数。
相反地；
a = 10.**(np.arange(-1, -8, -1))
幸运地，它给出了结果，因为10.0是一个浮点数。
编辑： 找到了一个支持我的观点的答案；为一个重复问题投了票：
https://stackoverflow.com/questions/43287311/why-cant-i-raise-to-a-negative-power-in-numpy
英文:
This is happening because the input 10 is an integer.
10**(np.arange(-1, -8, -1))
numpy.arange() is designed such a way that that has to give 10**(np.arange(-1, -8, -1)) integers or nothing since input is an integer.
On the contrary;
a = 10.**(np.arange(-1, -8, -1)
gives results happily as 10.0 is a float
Edit: found an answer to back my point; voted for a duplicate:
https://stackoverflow.com/questions/43287311/why-cant-i-raise-to-a-negative-power-in-numpy
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