stats_cdf_poisson

(PECL stats >= 1.0.0)

stats_cdf_poisson — Calculates any one parameter of the Poisson distribution given values for the others.

说明

float stats_cdf_poisson ( float $par1 , float $par2 , int $which )

Returns the cumulative distribution function, its inverse, or one of its parameters, of the Poisson distribution. The kind of the return value and parameters (par1 and par2) are determined by which.

The following table lists the return value and parameters by which. CDF, x, and lambda denotes cumurative distribution function, the value of the random variable, and the parameter of the Poisson distribution, respectively.

Return value and parameters
which Return value par1 par2
1 CDF x lambda
2 x CDF lambda
3 lambda x CDF

参数

par1

The first parameter

par2

The second parameter

which

The flag to determine what to be calculated

返回值

Returns CDF, x, or lambda, determined by which.

User Contributed Notes

s at nder dot com 23-Nov-2012 06:33
A simple poisson-distribution function, which only works for relatively small numbers (maximum of ~100/100 for most systems):

<?php

function factorial($number)
{
        if ($number < 2) {
                return 1;
        } else {
                return ($number * factorial($number-1));
        }
}

function poisson($chance, $occurrence)
{
        $e = exp(1);

        $a = pow($e, (-1 * $chance));
        $b = pow($chance,$occurrence);
        $c = factorial($occurrence);

        return $a * $b / $c;
}

$test = poisson(100,100);
echo $test . "\n";

?>