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Math.Log Method (Double)

Returns the natural (base e) logarithm of a specified number.

Namespace:  System
Assemblies:   mscorlib (in mscorlib.dll)
  System.Runtime.Extensions (in System.Runtime.Extensions.dll)

public static double Log(
	double d
)

Parameters

d
Type: System.Double

The number whose logarithm is to be found.

Return Value

Type: System.Double
One of the values in the following table.

d parameter

Return value

Positive

The natural logarithm of d; that is, ln d, or log e d

Zero

NegativeInfinity

Negative

NaN

Equal to NaN

NaN

Equal to PositiveInfinity

PositiveInfinity

Parameter d is specified as a base 10 number.

The following example illustrates the Log method.

using System;
public class Example
{
   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[] XArgs = { 1.2, 4.9, 9.9, 0.1 };

      foreach (double argX in XArgs)
      {
         // Find natural log of argX.
         Console.WriteLine("                      Math.Log({0}) = {1:E16}",
                           argX, Math.Log(argX));

         // Evaluate 1 / log[X](e).
         Console.WriteLine("             1.0 / Math.Log(e, {0}) = {1:E16}",
                           argX, 1.0 / Math.Log(Math.E, argX));
         Console.WriteLine();
      }
   }   
}
// This example displays the following output: 
//         Evaluate this identity with selected values for X: 
//                                     ln(x) = 1 / log[X](B) 
//        
//                             Math.Log(1.2) = 1.8232155679395459E-001 
//                    1.0 / Math.Log(e, 1.2) = 1.8232155679395459E-001 
//        
//                             Math.Log(4.9) = 1.5892352051165810E+000 
//                    1.0 / Math.Log(e, 4.9) = 1.5892352051165810E+000 
//        
//                             Math.Log(9.9) = 2.2925347571405443E+000 
//                    1.0 / Math.Log(e, 9.9) = 2.2925347571405443E+000 
//        
//                             Math.Log(0.1) = -2.3025850929940455E+000 
//                    1.0 / Math.Log(e, 0.1) = -2.3025850929940455E+000

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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