This is the statistics extension. It contains few dozens of functions useful for statistical computations. It is a wrapper around 2 scientific libraries, namely DCDFLIB (Library of C routines for Cumulative Distributions Functions, Inverses, and Other parameters) by B. Brown & J. Lavato and RANDLIB by Barry Brown, James Lavato & Kathy Russell. Includes CD and PD functions.
This PECL extension is not bundled with PHP.
Additional information such as new releases, downloads, source files, maintainer information, and a CHANGELOG, can be located here: http://pecl.php.net/package/stats.
No external libraries are needed. The extension comes bundled with the libraries used.