C# / .NET - Math.Log() method example

The Math.Log() method returns the natural logarithm (base e) of a number. 

using System;

public class Program
{
    public static void Main(string[] args) 
    {
        // Natural logarithm (logarithm with base e):
        //                           x            y
        Console.WriteLine( Math.Log( 1    ) ); // 0
        Console.WriteLine( Math.Log( 7    ) ); // 1.9459101490553132
        Console.WriteLine( Math.Log( 10   ) ); // 2.3025850929940460
        Console.WriteLine( Math.Log( 100  ) ); // 4.6051701859880920
        Console.WriteLine( Math.Log( 1000 ) ); // 6.9077552789821370

        Console.WriteLine( Math.Log( -1                      ) ); // NaN
        Console.WriteLine( Math.Log(  0                      ) ); // -∞ / -Infinity
        Console.WriteLine( Math.Log( Double.PositiveInfinity ) ); //  ∞ / +Infinity

        Console.WriteLine( Math.E ); // 2.718281828459045

        // Logarithm with custom base is placed in the below example.
    }
}

The Math.Log() method is presented on the following chart:

1. Documentation

namespace System
{
    public static class Math
    {
        // ...
        public static double Log(double a, double newBase) { ... }
        public static double Log(double d) { ... }
        // ...
    }
}

2. Logarithm with custom base example

This example shows a logarithmic function calculation with its own base.

using System;

public class Program
{
    static double calculateLogarithm(double logBase, double x) 
    {
        double a = Math.Log(x);     
        double b = Math.Log(logBase);

        return a / b;
    }

    public static void Main(string[] args) 
    {
        // Logarithm with custom base:
        //                                    base     x               y
        Console.WriteLine( calculateLogarithm( 2,      2      ) ); //  1
        Console.WriteLine( calculateLogarithm( 2,      4      ) ); //  2
        Console.WriteLine( calculateLogarithm( Math.E, Math.E ) ); //  1
        Console.WriteLine( calculateLogarithm( 3,      9      ) ); //  2
        Console.WriteLine( calculateLogarithm( 3,      81     ) ); //  4
        Console.WriteLine( calculateLogarithm( 10,     10     ) ); //  1
    }
}

References

1. Natural logarithm - Wikipedia