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VBScript in a Nutshell, 2nd Edition by Ron Petrusha, Matt Childs, Paul Lomax

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Name

Log Function

Syntax

Log(number)
number

Use: Required

Data Type: Double

A numeric expression greater than zero.

Return Value

A Double.

Description

Returns the natural logarithm of a given number.

Rules at a Glance

  • The natural logarithm is based on e, a constant whose value is approximately 2.718282. The natural logarithm is expressed by the equation:

    ez = x

    where z = Log(x). In other words, the natural logarithm is the inverse of the exponential function.

  • number, 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.”

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:

    Function Log10(X)
       Log10 = Log(X) / Log(10)
    End Function
  • A number of other mathematical functions that aren’t intrinsic to VBScript can be computed using the value returned by the Log function. The functions and their formulas are:

    Inverse Hyperbolic Sine

    HArcsin(X) = Log(X + Sqr(X * X + 1))

    Inverse Hyperbolic Cosine

    HArccos(X) = Log(X + Sqr(X * X - 1))

    Inverse Hyperbolic Tangent

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

    Inverse Hyperbolic Secant

    HArcsec(X) = Log((Sqr(-X * X + 1) + 1) / X)

    Inverse Hyperbolic Cosecant

    HArccosec(X) ...

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