numpy计算错误 [英] Numpy is calculating wrong

问题描述

我正在像这样的代码使用numpy

I am using numpy like this code

>>>import numpy as np
>>>a=np.arange(1,100000001).sum()
>>>a
987459712

我猜结果一定是这样的 5000000050000000

I guess the result must be some like 5000000050000000

我注意到直到五个数字，结果还是可以的. 有人知道发生了什么事吗?

I noticed that until five numbers the result is ok. Does someone knows what is happened?

致谢

推荐答案

Numpy在这里没有犯错.这种现象称为整数溢出.

Numpy is not doing a mistake here. This phenomenon is known as integer overflow.

x = np.arange(1,100000001)
print(x.sum())  # 987459712
print(x.dtype)  # dtype('int32')

在arange中用于给定输入的32位整数类型不能容纳5000000050000000.最多可以使用 2147483647 .

The 32 bit integer type used in arange for the given input simply cannot hold 5000000050000000. At most it can take 2147483647.

如果显式使用较大的整数或浮点数据类型，则将获得预期的结果.

If you explicitly use a larger integer or floating point data type you get the expected result.

a = np.arange(1, 100000001, dtype='int64').sum()
print(a)  # 5000000050000000

a = np.arange(1.0, 100000001.0).sum()
print(a)  # 5000000050000000.0

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