如何找到数字的指数？ [重复]

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Using log base 10 in a formula in Java 5 answers

在Java 5答案的公式中使用日志库10

Is there a method in the Java library that I can use to find the exponent of a number? Example: If I enter 100, then I expect a return value of 2 (since 10² = 100). If I enter 10000, then I expect a return value of 4 (since 10⁴ = 10000).

在Java库中是否有一个方法可以用来查找数字的指数?示例:如果我输入100,那么我希望返回值为2(因为102 = 100)。如果我输入10000,那么我期望返回值为4(因为104 = 10000)。

Or do I have to keep a counter and keep computing 10^counter and check if that is my number. If yes return the counter else increment the counter by 1 and repeat.

或者我必须保留一个计数器并继续计算10counter并检查这是否是我的号码。如果是,则返回计数器,否则将计数器增加1并重复。

2 个解决方案

#1

What you're looking for is the logarithm:

你要找的是对数:

Math.log10(100); //yields 2.

Definition from google:

谷歌的定义:

Logarithm: a quantity representing the power to which a fixed number (the base) must be raised to produce a given number.

对数:表示必须提高固定数字(基数)以产生给定数字的功率的数量。

And the doc comments of Math.log10 state:

Math.log10的文档注释表示:

Returns the base 10 logarithm of a double value

返回double值的基数10对数

#2

Math.log10() is the standard function found in Math library:

Math.log10()是Math库中的标准函数:

public static double log10(double a)

public static double log10(double a)

Returns the base 10 logarithm of a double value. Special cases:

返回double值的基数10对数。特别案例:

• If the argument is NaN or less than zero, then the result is NaN.

•如果参数为NaN或小于零,则结果为NaN。

• If the argument is positive infinity, then the result is positive infinity.

•如果参数为正无穷大,则结果为正无穷大。

• If the argument is positive zero or negative zero, then the result is negative infinity.

•如果参数为正零或负零,则结果为负无穷大。

• If the argument is equal to 10n for integer n, then the result is n.

•如果整数n的参数等于10n,则结果为n。

The computed result must be within 1 ulp of the exact result. Results must be semi-monotonic.

计算结果必须在精确结果的1 ulp范围内。结果必须是半单调的。

#1