# Distribution Quick Start

git clone https://github.com/sciruby/distribution

## Description:

Statistical Distributions library. Includes Normal univariate and bivariate, T, F, Chi Square, Binomial, Hypergeometric, Exponential, Poisson, Beta, LogNormal and Gamma.

Uses Ruby by default and C (statistics2/GSL) or Java extensions where available.

Includes code from statistics2 on Normal, T, F and Chi Square ruby code [http://blade.nagaokaut.ac.jp/~sinara/ruby/math/statistics2]

## Synopsis:

• Returns Gaussian PDF for x pdf=Distribution::Normal.pdf(x)
• Returns Gaussian CDF for x cdf=Distribution::Normal.cdf(x)
• Returns inverse CDF (or p-value) for x pv=Distribution::Normal.p_value(x)

## System Requirements:

To increase (notably!) the speed, please install

• Ruby 1.9-2.1: rb-gsl
• Java: Not yet implemented

## User Installation:

gem install distribution

To speep up

gem install gsl

## Developers:

After checking out the source, run:

\$ rake newb

This task will install any missing dependencies, run the tests/specs, and generate the RDoc.

If you want to provide a new distribution, /lib/distribution run

\$ distribution --new your_distribution

This should create the main distribution file, the directory with ruby and gsl engines and the rspec on /spec directory.

### API Structure

Distribution::.(cdf|pdf|p_value|rng)

On discrete distributions, exact Ruby implementations of pdf, cdf and p_value could be provided, using

Distribution::<name>.exact_(cdf|pdf|p_value)

module Distribution::Shorthand provides (you guess?) shortands method to call all methods

<Distribution shortname>_(cdf|pdf|p|r)

On discrete distributions, exact cdf, pdf and p_value are

<Distribution shortname>_(ecdf|epdf|ep)

Shortnames for distributions:

• Normal: norm
• Bivariate Normal: bnor
• T: tdist
• F: fdist
• Chi Square: chisq
• Binomial: bino
• Hypergeometric: hypg
• Exponential: expo
• Poisson: pois
• Beta: beta
• Gamma: gamma
• LogNormal: lognormal

### API Structure Example

Distribution::T.cdf

could be called after including Distribution::Shorthand

tdist_cdf

## Features

• Very fast ruby 1.8.7/1.9.+ implementation, with improved method to calculate factorials and others common functions
• All methods tested on several ranges. See spec/

## Issues

• On Jruby and Rubinius, BivariateNormal returns incorrect pdf

For current issues see the issue tracker pages