为什么 NaN^0 == 1 [英] Why does NaN^0 == 1

问题描述

受到早期代码打高尔夫球的提示，为什么会:

Prompted by a spot of earlier code golfing why would:

>NaN^0
[1] 1

NA^0 为 1 是完全合理的，因为 NA 缺少数据，并且 任何 数字提高为 0 将给出 1，包括-Inf和Inf.然而 NaN 应该代表 not-a-number，那么为什么会这样呢?当 ?NaN 的帮助页面指出:

It makes perfect sense for NA^0 to be 1 because NA is missing data, and any number raised to 0 will give 1, including -Inf and Inf. However NaN is supposed to represent not-a-number, so why would this be so? This is even more confusing/worrying when the help page for ?NaN states:

在 R 中，基本上所有的数学函数(包括基本的Arithmetic)，应该与 +/- Inf 和 NaN 一起正常工作输入或输出.

In R, basically all mathematical functions (including basic Arithmetic), are supposed to work properly with +/- Inf and NaN as input or output.

基本规则应该是Inf的调用和关系确实是具有适当数学限制的语句.

The basic rule should be that calls and relations with Infs really are statements with a proper mathematical limit.

涉及NaN 的计算将返回NaN 或NA:哪个这两个不能保证，可能取决于 R 平台(因为编译器可能会重新排序计算).

Computations involving NaN will return NaN or perhaps NA: which of those two is not guaranteed and may depend on the R platform (since compilers may re-order computations).

这背后是否有哲学上的原因，还是仅仅与 R 表示这些常量的方式有关?

Is there a philosophical reason behind this, or is it just to do with how R represents these constants?

推荐答案

这个在?'NaN'

IEC 60559 标准，也称为 ANSI/IEEE 754 浮点标准.

"The IEC 60559 standard, also known as the ANSI/IEEE 754 Floating-Point Standard.

http://en.wikipedia.org/wiki/NaN."

然后你会发现关于什么应该创建 NaN 的声明:

And there you find this statement regarding what should create a NaN:

 "There are three kinds of operations that can return NaN:[5]
       Operations with a NaN as at least one operand.

它可能来自特定的 C 编译器，如您引用的注释所示.这是 GNU C 文档所说的:

It is probably is from the particular C compiler, as signified by the Note you referenced. This is what the GNU C documentation says:

http://www.gnu.org/software/libc/manual/html_node/Infinity-and-NaN.html

另一方面，NaN 会感染任何涉及它的计算.除非无论用什么实际值替换 NaN，计算都会产生相同的结果，否则结果就是 NaN."

" NaN, on the other hand, infects any calculation that involves it. Unless the calculation would produce the same result no matter what real value replaced NaN, the result is NaN."

因此看来 GNU-C 人员在编写代码时有不同的标准.据报道，2008 版 ANSI/IEEE 754 浮点标准提出了该建议:

So it seems that the GNU-C people have a different standard in mind when writing their code. And the 2008 version of ANSI/IEEE 754 Floating-Point Standard is reported to make that suggestion:

http://en.wikipedia.org/wiki/NaN#Function_definition

已发布的标准不是免费的.因此，如果您有访问权限或金钱，您可以在这里查看:

The published standard is not free. So if you are have access rights or money you can look here:

http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=4610933

http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=4610933

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