Mean

Poisson distribution expected value.

The expected value for a Poisson random variable is

where λ is the mean parameter.

Installation

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

Usage

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

mean( lambda )

Returns the expected value of a Poisson distribution with mean parameter lambda.

var v = mean( 9.0 );
// returns 9.0

v = mean( 0.5 );
// returns 0.5

If provided lambda < 0, the function returns NaN.

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

Examples

var uniform = require( '@stdlib/random-array-uniform' );
var logEachMap = require( '@stdlib/console-log-each-map' );
var mean = require( '@stdlib/stats-base-dists-poisson-mean' );

var opts = {
    'dtype': 'float64'
};
var lambda = uniform( 10, 0.0, 20.0, opts );

logEachMap( 'λ: %0.4f, E(X;λ): %0.4f', lambda, mean );

C APIs

Usage

#include "stdlib/stats/base/dists/poisson/mean.h"

stdlib_base_dists_poisson_mean( λ )

Returns the expected value of a Poisson distribution with mean parameter λ.

double out = stdlib_base_dists_poisson_mean( 0.5 );
// returns 0.5

The function accepts the following arguments:

• λ: [in] double mean parameter.

double stdlib_base_dists_poisson_mean( const double lambda );

Examples

#include "stdlib/stats/base/dists/poisson/mean.h"
#include <stdlib.h>
#include <stdio.h>

int main( void ) {
    double lambda;
    double v;
    int i;

    for ( i = 0; i < 10; i++ ) {
        lambda = 20.0 * (double)rand() / ( (double)RAND_MAX + 1.0 );
        v = stdlib_base_dists_poisson_mean( lambda );
        printf( "λ: %lf, E(X;λ): %lf\n", lambda, v );
    }
}

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

License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.