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ieee745gamma

1.0.1
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  • License MIT

The gamma and log(gamma) function

Package Exports

  • ieee745gamma

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (ieee745gamma) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

IEEE-754 compliant LogGamma function

The log(gamma) function in JavaScript as defined in IEEE-745.

browser support

Version

1.0.0

Introduction

This is a port of the implementation of lngamma by Sun Microsystems who published the original under the following license:

Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.

Developed at SunPro, a Sun Microsystems, Inc. business.
Permission to use, copy, modify, and distribute this
software is freely granted, provided that this notice
is preserved.

That license is compatible with the MIT license.

A normal gamma function is implemented, too, but only with Math.exp() which induces a large error, especially for larger numbers. See the examples for details.

To implement a better exponential function is planned for a later version.

Example

The correct results to 38 decimal digits in the comments

> var g = require('ieee745gamma')
> g.gamma(11)
3628800.0000000084      // 3628800.0000000000000000000000000000000
> g.gamma(171)
7.257415615308056e+306  // 7.2574156153079989673967282111292631147 E306
// errors of gamma due to Math.exp():
> g.lngamma(171)
706.5730622457874       // 706.57306224578734711072226272129831468
> g.lngamma(11)
15.104412573075518      // 15.104412573075515295225709329251070372
> g.lngamma(1000000)
12815504.569147611      // 12815504.569147611659976971785017113154
> g.lngamma(.0001)
9.210282658633961       // 9.2102826586339622584486579752729991548
> g.lngamma(3)
0.6931471805599453      // 0.69314718055994530941723212145817656808
> g.lngamma(3) - Math.log(2)
0                       // 0

Methods

gamma(x)

Returns exp(log(gamma(x))) for real x, x not a negative integer, over the range of ca. -177.6 <= x <= 171.7, Infinity otherwise.

lngamma(x)

Returns log(gamma(x)) for real x, x not a negative integer, over the range of ca. -10^14 <= x <= 10^305, Infinity otherwise.

Install

With npm do:

npm install ieee745gamma

License

MIT