Microsoft KB Archive/87863

= Microsoft Knowledge Base =

Excel: ATP Definition: GAMMALN
Last reviewed: January 30, 1996

Article ID: Q87863

The information in this article applies to:


 * Microsoft Excel for Windows 95, version 7.0
 * Microsoft Excel for Windows, versions 4.0, 5.0
 * Microsoft Excel for the Macintosh, versions 4.0, 5.0

SUMMARY
The versions of Microsoft listed above provide a set of special analysis tools called the Analysis ToolPak. This article is part of a series of articles that provide information on the underlying formulas used in the Analysis ToolPak.

This article covers the following function:

GAMMALN(x)

MORE INFORMATION
The GAMMALN function returns the natural logarithm of the gamma function for a particular value of the random variable X. The Excel function is implemented with the following C routine:

float gammln(xx) float xx;
 * 1) include 

{

double x,tmp,ser; static double cof[6]={76.18009173,-86.50532033,24.01409822,- 1.231739516,0.120858003e-2,-0.536382e-5};

int j; x=xx-1.0; tmp=x+5.5; ser=1.0; for (j=0;j<=5;j++){

x += 1.0; ser += cof[j]/x; } return -tmp+log(2.50662827465*); }

For large values of X, the GAMMALN function is often better to use than the GAMMADIST function because it is less likely to overflow a computer's floating point representation.