C＃| Math.Log()方法

在C＃中， Math.Log()是Math类方法。用于返回指定数字的对数。可以通过更改传递的参数数量来重载此方法。 Math.Log()方法的重载列表中总共有2种方法，如下所示：

• Math.Log(Double)方法
• Math.Log(Double，Double)方法

Math.Log(Double)方法

此方法用于返回指定数字的自然对数(以e为底)。

句法：

public static double Log(double val)

范围：

val: It is the specified number whose natural (base e) logarithm to be calculated and its type is System.Double.

返回值：返回val的自然对数，其类型为System.Double 。

注意：参数val总是以10为基数，返回值取决于传递的参数。以下是一些情况：

• 如果参数为正，则method将返回自然对数或log _e (val) 。
• 如果参数为零，则结果为NegativeInfinity 。
• 如果参数为Negative(小于零)或等于NaN ，则结果为NaN 。
• 如果参数为PositiveInfinity ，则结果为PositiveInfinity 。
• 如果参数为NegativeInfinity ，则结果为NaN 。

例子：

// C# program to demonstrate working
// of Math.Log(Double) method
using System;
  
class Geeks {
  
    // Main Method
    public static void Main(String[] args)
    {
  
        // double values whose logarithm 
        // to be calculated
        double a = 4.55;
        double b = 0;
        double c = -2.45;
        double nan = Double.NaN;
        double positiveInfinity = Double.PositiveInfinity;       
        double negativeInfinity = Double.NegativeInfinity;
  
        // Input is positive number so output
        // will be logarithm of number
        Console.WriteLine(Math.Log(a));
  
        // positive zero as argument, so output 
        // will be -Infinity
        Console.WriteLine(Math.Log(b));
  
        // Input is negative number so output
        // will be NaN
        Console.WriteLine(Math.Log(c));
  
        // Input is NaN so output
        // will be NaN
        Console.WriteLine(Math.Log(nan));
  
        // Input is PositiveInfinity so output
        // will be Infinity
        Console.WriteLine(Math.Log(positiveInfinity));
  
        // Input is NegativeInfinity so output
        // will be NaN
        Console.WriteLine(Math.Log(negativeInfinity));
    }
}

输出：

1.51512723296286
-Infinity
NaN
NaN
Infinity
NaN

Math.Log(Double，Double)方法

此方法用于以指定的底数返回指定数字的对数。

句法：

public static double Log(double val, double base)

范围：

val: It is the specified number whose logarithm to be calculated and its type is System.Double.

base: It is the base of the logarithm of type System.Double.

返回值：返回val的对数，类型为System.Double 。

注意：返回值始终取决于传递的参数。下表描述了不同的情况：

val	base	Returned Value
val > 0	(0 < Base < 1) or(Base > 1)	logbase(val)
val < 0	any value	NaN
any value	base < 0	NaN
val != 1	base = 0	NaN
val != 1	base = +ve Infinity	NaN
val = NaN	any value	NaN
any value	base = NaN	NaN
any value	base = 1	NaN
val = 0	(0 < Base < 1)	+ve Infinity
val = 0	base > 1	-ve Infinity
val = +ve Infinity	(0 < Base < 1)	-ve Infinity
val = +ve Infinity	base > 1	+ve Infinity
val = 1	base = 0	0
val = 1	base = +ve Infinity	0

例子：

// C# program to demonstrate working
// of Math.Log(Double, Double) method
using System;
  
class Geeks {
  
    // Main Method
    public static void Main(String[] args)
    {
  
        // Here val = 1.3 and base is 0.3 then 
        // output will be logarithm of given value
        Console.WriteLine(Math.Log(1.3, 0.3));
          
        // Here val is 0.5 and base > 1 then output 
        // will be -0.5
        Console.WriteLine(Math.Log(0.5, 4));
  
        // Here val is 0.7 and base = 1 then output 
        // will be NaN
        Console.WriteLine(Math.Log(0.7, 1));
  
        // Here val is 0.7 and base is NaN then output 
        // will be NaN
        Console.WriteLine(Math.Log(0.7, Double.NaN));
    }
}

输出：

-0.217915440884381
-0.5
NaN
NaN

参考：

• https://msdn.microsoft.com/zh-CN/library/x80ywz41(v=vs.110).aspx
• https://msdn.microsoft.com/zh-CN/library/hd50b6h5(v=vs.110).aspx