VB.NET Language in a Nutshell, Second Edition

Name

Log Function

Class

System.Math

Syntax

Math.Log(d)

or:

Math.Log(a, newbase)

d or a (required; Double)

A numeric expression greater than zero

newbase (required; Double)

The base of the logarithm

Return Value

Double

Description

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)

Rules at a Glance

• The natural logarithm is the logarithm base e, a constant whose value is approximately 2.718282. The natural logarithm satisfies the equation:

  e^Log(x) = x

  In other words, the natural logarithm function is the inverse function of the exponential function.

• d or a, the value whose natural logarithm the function is to return, must be a positive real number. If number is negative or zero, the function generates runtime error 5, “Invalid procedure call or argument.”

• This is a Shared member, so it can be used without creating any objects.

Programming Tips and Gotchas

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

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

  For example, the Log10 function shows the source code for a custom function that calculates base-10 logarithms:

  Static Function Log10(X)
     Log10 = 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 ...