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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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