Log Function

Log Function

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Class

System.Math

Syntax

     Dim result As Double = Math.Log  (d) 

or:

     Dim result As Double = Math.Log(a, newBase) 

d, a (required; Double)

A numeric expression greater than zero

newBase (required; Double)

The base of the logarithm

Description

The Log function returns the natural (base e) logarithm of a given number (the first syntax), or the logarithm of a given number in a specified base (the second syntax).

Usage at a Glance

• The Log function is the inverse of the Exp function.

• This is a shared member of the System.Math class, so it can be used without an instance.

• You can calculate base-n logarithms for any number, x, by dividing the natural logarithm of x by the natural logarithm of n:

       Logn(x) = Log(x) / Log(n) 

  
  

  For example, you can replicate the Log10 function using this method:

       Static Function Log10(ByVal x As Double) As Double        Return Log(x) / Log(10#)     End Function 

  
  

• The inverse trigonometric functions, which are not intrinsic to VB, can be computed using the value returned by the Log function. The functions and their formulas are:

  
  

  Inverse hyperbolic sine

  HArcsin(x) = Log(x + Sqrt(x * (x + 1)))

  
  

  Inverse hyperbolic cosine

  HArccos(x) = Log(x + Sqrt(x * (x - 1)))

  
  

  Inverse hyperbolic tangent

  HArctan(x) = Log((1 + x) / (1 - x)) / 2

  
  

  Inverse hyperbolic secant

  HArcsec(x) = Log((Sqrt(-x * (x + 1)) + 1) / x)

  
  

  Inverse hyperbolic cosecant

  HArccosec(x) = Log((Sign(x) * _

       Sqrt(x * x + 1) + 1) / x) 

  
  

  
  

  Inverse hyperbolic cotangent

  HArccotan(x) = Log((x + 1) / (x - 1)) / 2

See Also

Exp Function, Log10 Function