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# C# | Math.Log() Method

• Last Updated : 31 Jan, 2019

In C#, Math.Log() is a Math class method. It is used to return the logarithm of a specified number. This method can be overloaded by changing the number of the arguments passed. There are total 2 methods in the overload list of the Math.Log() method as follows:

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

##### Math.Log(Double) Method

This method is used to return the natural (base e) logarithm of a specified number.

Syntax:

`public static double Log(double val)`

Parameter:

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

Return Value: Returns the natural logarithm of val and its type is System.Double.

Note: Parameter val is always specified as a base 10 number.The return value is depend on the argument passed. Below are some cases:

• If the argument is positive then method will return the natural logarithm or loge(val).
• If the argument is zero, then the result is NegativeInfinity.
• If the argument is Negative(less than zero) or equal to NaN, then the result is NaN.
• If the argument is PositiveInfinity, then the result is PositiveInfinity.
• If the argument is NegativeInfinity, then the result is NaN.

Example:

 `// 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));``    ``}``}`
Output:
```1.51512723296286
-Infinity
NaN
NaN
Infinity
NaN
```
##### Math.Log(Double, Double) Method

This method is used to return the logarithm of a specified number in a specified base.

Syntax:

`public static double Log(double val, double base)`

Parameter:

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.

Return Value: It returns the logarithm of val and its type is System.Double.

Note: The return value is always depend on the argument passed. Below table depicts the different cases:

valbaseReturned Value
val > 0(0 < Base < 1) or(Base > 1)logbase(val)
val < 0any valueNaN
any valuebase < 0NaN
val != 1base = 0NaN
val != 1base = +ve InfinityNaN
val = NaNany valueNaN
any valuebase = NaNNaN
any valuebase = 1NaN
val = 0(0 < Base < 1)+ve Infinity
val = 0base > 1-ve Infinity
val = +ve Infinity(0 < Base < 1)-ve Infinity
val = +ve Infinitybase > 1+ve Infinity
val = 1base = 00
val = 1base = +ve Infinity0

Example:

 `// 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));``    ``}``}`
Output:
```-0.217915440884381
-0.5
NaN
NaN
```

References:

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