XNUMBERS 5.0

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I was referred to this Excel add-in more than a year ago in the Lounge. Version 4.3 was available at the moment. Well today I needed to use the incomplete Gamma function and couldn’t find it neither in Excel’s built in formulas nor in XNUMBERS 4.3, so I decided to Google for an add-in / VBA code, and came up with XNUMBERS 5.0 — now featuring the incomplete Gamma function among other things I haven’t checked yet!:

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XNUMBERS 5.0 – Multi Precision Floating Point Computing and Numerical Methods for EXCEL

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Thanks for the link! I just installed it and it looks great. Now I can use Excel more often without having to always go to Maple. So far it seems to work on Excel 97 even though it talked only about 2000 or XP.

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I remember way back at Excel 4, being staggered at the thickness of a large book, covering specifically and only gamma functions in Excel. I shuddered to think of how big a book would be, covering ALL of XL, even back in those “lightweight” days.

Alan

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Well, this belongs more to the Excel forum, but to round ideas, I’ve found a way to use the incomplete Gamma function in Excel without any plugin.

Let the incomplete Gamma function be defined as in the left equation of the attached (the one to its right is the complete Gamma function). For a random variable X having a Gamma distribution with parameters Alpha and Theta, F(x) = Gamma(Alpha; x/Theta). Note that if Theta = 1, then F(x) = Gamma(Alpha; x).
In Excel there’s the GammaDist(x; Alpha; Beta; [Cumulative]) function (Beta is what I called Theta). So, GammaDist(x; Alpha; 1; 1) returns the desired incomplete gamma function.

The XNUMBERS xGammaI() function only allows for Alpha up to 170 or something. This Excel workaround allows for a wider range of values, although it seems that results become innacurate when parameters are too big (say, Alpha = 2000). It’s something I’m testing right now.

I need to work with large values of Alpha since I’m fitting a Gamma distribution to a data set and finding the estimates of the parameters Alpha and Theta by a method of minimizing a certain function of both the empirical and the theoretical distributions. I’m using the Solver tool to minimize this function and Alpha seems to be BIG. But I realize the result is unreliable as Excel fails to calculate the Gamma(Alpha;x) function alright.

Back to XNUMBERS, it features a Function Manager I hadn’t noticed. It’s pretty slick and provides quick access to a help file. Another pro

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