@stdlib/stats-base-dists-poisson-pmf
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    0.0.5 • Public • Published

    Probability Mass Function

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    Poisson distribution probability mass function (PMF).

    The probability mass function (PMF) for a Poisson random variable is

    Probability mass function (PMF) for a Poisson distribution.

    where lambda > 0 is the mean parameter.

    Installation

    npm install @stdlib/stats-base-dists-poisson-pmf

    Usage

    var pmf = require( '@stdlib/stats-base-dists-poisson-pmf' );

    pmf( x, lambda )

    Evaluates the probability mass function (PMF) of a Poisson distribution with mean parameter lambda.

    var y = pmf( 4.0, 3.0 );
    // returns ~0.168
    
    y = pmf( 1.0, 3.0 );
    // returns ~0.149
    
    y = pmf( -1.0, 2.0 );
    // returns 0.0

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

    var y = pmf( NaN, 2.0 );
    // returns NaN
    
    y = pmf( 0.0, NaN );
    // returns NaN

    If provided a negative mean parameter lambda, the function returns NaN.

    var y = pmf( 2.0, -1.0 );
    // returns NaN
    
    y = pmf( 4.0, -2.0 );
    // returns NaN

    If provided lambda = 0, the function evaluates the PMF of a degenerate distribution centered at 0.0.

    var y = pmf( 2.0, 0.0 );
    // returns 0.0
    
    y = pmf( 0.0, 0.0 );
    // returns 1.0

    pmf.factory( lambda )

    Returns a function for evaluating the probability mass function (PMF) of a Poisson distribution with mean parameter lambda.

    var mypmf = pmf.factory( 1.0 );
    var y = mypmf( 3.0 );
    // returns ~0.061
    
    y = mypmf( 1.0 );
    // returns ~0.368

    Examples

    var randu = require( '@stdlib/random-base-randu' );
    var round = require( '@stdlib/math-base-special-round' );
    var pmf = require( '@stdlib/stats-base-dists-poisson-pmf' );
    
    var lambda;
    var x;
    var y;
    var i;
    
    for ( i = 0; i < 10; i++ ) {
        x = round( randu() * 10.0 );
        lambda = randu() * 10.0;
        y = pmf( x, lambda );
        console.log( 'x: %d, λ: %d, P(X=x;λ): %d', x, lambda.toFixed( 4 ), y.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.

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    License

    See LICENSE.

    Copyright

    Copyright © 2016-2021. The Stdlib Authors.

    Install

    npm i @stdlib/stats-base-dists-poisson-pmf

    Homepage

    stdlib.io

    DownloadsWeekly Downloads

    39

    Version

    0.0.5

    License

    Apache-2.0

    Unpacked Size

    62.3 kB

    Total Files

    11

    Last publish

    Collaborators

    • stdlib-bot
    • kgryte
    • planeshifter
    • rreusser