I was wondering how to get the inverse of power in Ruby?
我想知道如何在Ruby中获得相反的功效？
2 ** 4 # => 16
and then I would like to get the inverse of it, and I'm not sure which operator to use
然后我想得到它的反转，我不确定使用哪个运算符
16 ?? 2 # => 4
5 个解决方案
#1
61
The inverse of exponentiation is the logarithm. If ab = c, then logac = b.
取幂的倒数是对数。如果ab = c，那么logac = b。
You can find logarithm functions in the Math module, specifically log() for base-e and log10() for base-10.
您可以在Math模块中找到对数函数，特别是base-e的log（）和base-10的log10（）。
To get a logarithm to a different base (say n), use the formula logNa = logxa/logxN, where x is a value such as e or 10.
要获得不同基数（比如n）的对数，请使用公式logNa = logxa / logxN，其中x是e或10等值。
For your specific case:
对于您的具体情况：
log216
= loge16/loge2
= Math.log(16) / Math.log(2)
= 4log216 = loge16 / loge2 = Math.log（16）/ Math.log（2）= 4
Whether you consider the explanation good because it expands your knowledge, or bad because you hated high school math, is entirely up to you :-)
你是否认为这个解释是好的，因为它扩展了你的知识，或者因为你讨厌高中数学而不好，完全取决于你:-)
#2
5
Math.log(16) / Math.log(2)
#3
4
Or alternatively, do it this way:
或者，也可以这样做：
>> 16**(1.0/2)
=> 4.0
#4
0
Actually:
其实：
- Maro is factually correct but
- Maro事实上是正确的但是
- Maro comment does not support Jeremy Murray-Wakefield's answer, which does not apply to the OP's question.
- Maro评论不支持Jeremy Murray-Wakefield的答案，这不适用于OP的问题。
Maro is therefore "right" on his own but not as a support for Jeremy Murray-Wakefields answer, which itself is not so much "wrong" as not the right answer to the OP's questions.
因此，Maro自己是“正确的”，但并不支持Jeremy Murray-Wakefields的答案，而这本身并不是“错误的”，而不是OP问题的正确答案。
Hope that's definitive!
希望这是肯定的！
#5
0
A cleaner way to obtain the logarithm, starting with Ruby 1.9.1, would be to use Math.log2:
从Ruby 1.9.1开始，获取对数的更简洁方法是使用Math.log2：
[1] pry(main)> Math.log2(2**4)
=> 4.0
#1
61
The inverse of exponentiation is the logarithm. If ab = c, then logac = b.
取幂的倒数是对数。如果ab = c，那么logac = b。
You can find logarithm functions in the Math module, specifically log() for base-e and log10() for base-10.
您可以在Math模块中找到对数函数，特别是base-e的log（）和base-10的log10（）。
To get a logarithm to a different base (say n), use the formula logNa = logxa/logxN, where x is a value such as e or 10.
要获得不同基数（比如n）的对数，请使用公式logNa = logxa / logxN，其中x是e或10等值。
For your specific case:
对于您的具体情况：
log216
= loge16/loge2
= Math.log(16) / Math.log(2)
= 4log216 = loge16 / loge2 = Math.log（16）/ Math.log（2）= 4
Whether you consider the explanation good because it expands your knowledge, or bad because you hated high school math, is entirely up to you :-)
你是否认为这个解释是好的，因为它扩展了你的知识，或者因为你讨厌高中数学而不好，完全取决于你:-)
#2
5
Math.log(16) / Math.log(2)
#3
4
Or alternatively, do it this way:
或者，也可以这样做：
>> 16**(1.0/2)
=> 4.0
#4
0
Actually:
其实：
- Maro is factually correct but
- Maro事实上是正确的但是
- Maro comment does not support Jeremy Murray-Wakefield's answer, which does not apply to the OP's question.
- Maro评论不支持Jeremy Murray-Wakefield的答案，这不适用于OP的问题。
Maro is therefore "right" on his own but not as a support for Jeremy Murray-Wakefields answer, which itself is not so much "wrong" as not the right answer to the OP's questions.
因此，Maro自己是“正确的”，但并不支持Jeremy Murray-Wakefields的答案，而这本身并不是“错误的”，而不是OP问题的正确答案。
Hope that's definitive!
希望这是肯定的！
#5
0
A cleaner way to obtain the logarithm, starting with Ruby 1.9.1, would be to use Math.log2:
从Ruby 1.9.1开始，获取对数的更简洁方法是使用Math.log2：
[1] pry(main)> Math.log2(2**4)
=> 4.0