目标c /可可触摸中有什么样的对数函数/方法？ [英] What kind of logarithm functions / methods are available in objective-c / cocoa-touch?

问题描述

我试过搜索logarithm + objective-c，但我所得到的是教师的数学测试页，或解释对数是什么）。

I've tried searching for logarithm + objective-c, but all I get is math test pages from teachers, or explanations what a logarithm is ;)

有一些测量，像83912.41234和其他人是32.94232。我需要把这个巨大的频谱压缩到0到100之间，32.94232将至少是大于2的东西，其中83912.41234将是接近100.所以我认为对数函数将是我的朋友在这里。

I've got some measurements that are like 83912.41234 and others are 32.94232. I need to press down this huge spectrum into something between 0 and 100, and that 32.94232 would habe to be at least something bigger than 2, where the 83912.41234 would be something near 100. So I think a logarithm function will be my friend here.

更新：
我通过快速打开（在Xcode中非常漂亮的命令：SHIFT + CMD + D）遇到math.h文件，有惊喜：

UPDATE: I've came across the math.h file through "Open Quickly" (very nice command in Xcode: SHIFT + CMD + D), and there, big surprise:

extern double log ( double );
extern float logf ( float );

extern double log10 ( double );
extern float log10f ( float );

extern double log2 ( double );
extern float log2f ( float );

extern double log1p ( double );
extern float log1pf ( float );

extern double logb ( double );
extern float logbf ( float );

但是：没有文字，没有注释。我不是一个数学家。因此，一些描述将是好的，即什么样的对数的情况下，曲线的外观，等等。所以任何伟大的链接，高度赞赏！

But: No text, no comments. I'm not such a math-freak. So some description would be good, i.e. what kind of logarithm for what case, how the curve looks like, etc... so any great links are highly appreciated!

推荐答案

此外，获取任意基数的对数：

Also, getting a logarithm with an arbitrary base:

float logx(float value, float base) 
{
   return log10f(value) / log10f(base);
}

这篇关于目标c /可可触摸中有什么样的对数函数/方法？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！