python math.log函数中的数学域错误 [英] python math domain errors in math.log function

问题描述

我必须使用Python math.log(x)函数，其值从(0，...，1)为 x .有时x可能太接近零，而Python给我一个错误:

I have to use Python math.log(x) function with values of x from (0, ..., 1). Sometimes x may be too close to zero, and Python gives me an error:

ValueError:数学域错误

ValueError: math domain error

我怎么知道 math.log 函数的定义范围是什么?

How can I know, what is the domain of definition of math.log function?

推荐答案

只要您的输入在半开间隔(0，1](不包括0)之内，就可以了.接近零:

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:

>>> math.log(sys.float_info.min)
-708.3964185322641

因此仅检查零(可能是下溢的结果)就足够了，或者捕获异常并进行处理.

So simply checking for exactly zero (maybe as the result of an underflow) should be enough, or alternatively catch the exception and handle it.

编辑:这也适用于非正常的最小浮点数:

EDIT: This also holds for the denormal minimum floating point number:

>>> math.log(sys.float_info.min * sys.float_info.epsilon)
-744.4400719213812

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