# Double - Log

Returns the logarithm of a specified number in a specified base.

```public static void Main()
{
Console.WriteLine("  Evaluate this identity with selected values for X:");
Console.WriteLine("                              ln(x) = 1 / log[X](B)");
Console.WriteLine();

double[] values = { 1.2, 4.9, 9.9, 0.1 };

foreach (double value in values)
{
// C# Extension Method: Double - Log
Console.WriteLine("                      Log({0}) = {1:E16}", value, value.Log());

// C# Extension Method: Double - Log
double e = Math.E;
Console.WriteLine("             1.0 / Log(e, {0}) = {1:E16}", value, 1.0 / e.Log(value));
Console.WriteLine();
}
}
```

View Source
```using System;

public static partial class Extensions
{
/// <summary>
///     Returns the natural (base e) logarithm of a specified number.
/// </summary>
/// <param name="d">The number whose logarithm is to be found.</param>
/// <returns>
///     One of the values in the following table.  parameterReturn value Positive The natural logarithm of ; that is,
///     ln , or log eZero Negative Equal to Equal to.
/// </returns>
public static Double Log(this Double d)
{
return Math.Log(d);
}

/// <summary>
///     Returns the logarithm of a specified number in a specified base.
/// </summary>
/// <param name="d">The number whose logarithm is to be found.</param>
/// <param name="newBase">The base of the logarithm.</param>
/// <returns>
///     One of the values in the following table. (+Infinity denotes , -Infinity denotes , and NaN denotes .)Return
///     value&gt; 0(0 &lt;&lt; 1) -or-(&gt; 1)lognewBase(a)&lt; 0(any value)NaN(any value)&lt; 0NaN != 1 = 0NaN != 1
///     = +InfinityNaN = NaN(any value)NaN(any value) = NaNNaN(any value) = 1NaN = 00 &lt;&lt; 1 +Infinity = 0&gt; 1-
///     Infinity =  +Infinity0 &lt;&lt; 1-Infinity =  +Infinity&gt; 1+Infinity = 1 = 00 = 1 = +Infinity0.
/// </returns>
/// ###
/// <param name="a">The number whose logarithm is to be found.</param>
public static Double Log(this Double d, Double newBase)
{
return Math.Log(d, newBase);
}
}
```