# npm

## @stdlib/stats-base-dists-negative-binomial-mean 0.0.8 • Public • Published

# Mean

Negative binomial distribution expected value.

The mean for a negative binomial random variable is

where r is the number of successes until experiment is stopped and p is the success probability in each trial. The random variable X denotes the number of failures until the r success is reached.

## Installation

npm install @stdlib/stats-base-dists-negative-binomial-mean

## Usage

var mean = require( '@stdlib/stats-base-dists-negative-binomial-mean' );

#### mean( r, p )

Returns the expected value of a negative binomial distribution with parameters r (number of successes until experiment is stopped) and p (success probability).

var v = mean( 100, 0.2 );
// returns 400

v = mean( 50, 0.5 );
// returns 50

If provided NaN as any argument, the function returns NaN.

var v = mean( NaN, 0.5 );
// returns NaN

v = mean( 20, NaN );
// returns NaN

If provided a r which is not a positive number, the function returns NaN.

var v = mean( -2.0, 0.5 );
// returns NaN

If provided a success probability p outside of [0,1], the function returns NaN.

var v = mean( 20, -1.0 );
// returns NaN

v = mean( 20, 1.5 );
// returns NaN

## Examples

var randu = require( '@stdlib/random-base-randu' );
var mean = require( '@stdlib/stats-base-dists-negative-binomial-mean' );

var v;
var i;
var r;
var p;

for ( i = 0; i < 10; i++ ) {
r = randu() * 100;
p = randu();
v = mean( r, p );
console.log( 'r: %d, p: %d, E(X;r,p): %d', r, p.toFixed( 4 ), v.toFixed( 4 ) );
}

## Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

#### Community ## Keywords

### Install

npm i @stdlib/stats-base-dists-negative-binomial-mean

stdlib.io

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0.0.8