math.log 函数中的 python 数学域错误
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/19095774/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
python math domain errors in math.log function
提问by Felix
I have to use Python math.log(x)function with values of xfrom (0, ..., 1). Sometimes x may be too close to zero, and Python gives me an error:
我必须使用 Pythonmath.log(x)函数和xfrom (0, ..., 1) 的值。有时 x 可能太接近于零，Python 给我一个错误：
ValueError: math domain error
ValueError：数学域错误
How can I know, what is the domain of definition of math.logfunction?
我怎么知道，math.log函数定义的域是什么？
采纳答案by Sven Marnach
As long as your input is within the half-open interval (0, 1] (not including 0), you are fine. You can't be too close to zero:
只要您的输入在半开区间 (0, 1] (不包括 0) 内，您就可以了。您不能太接近于零：
>>> math.log(sys.float_info.min)
-708.3964185322641
So simply checking for exactly zero (maybe as the result of an underflow) should be enough, or alternatively catch the exception and handle it.
所以简单地检查零（可能是下溢的结果）就足够了，或者捕获异常并处理它。
EDIT: This also holds for the denormal minimum floating point number:
编辑：这也适用于非正规最小浮点数：
>>> math.log(sys.float_info.min * sys.float_info.epsilon)
-744.4400719213812
回答by ismail
You are going over the supported precision, use Decimalclass instead.
您正在检查支持的精度，请改用Decimal类。
>>> from math import log
>>> from decimal import Decimal
>>> d = Decimal('1E-1024')
>>> log(d)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: math domain error
>>> d.ln()
Decimal('-2357.847135225902780434423250')
