stats_cdf_poisson

(PECL stats >= 1.0.0)

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

Description

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

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 cumulative 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

Parameters

par1: The first parameter
par2: The second parameter
which: The flag to determine what to be calculated

Return Values

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

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User Contributed Notes 1 note

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s at nder dot com ¶

12 years ago

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";

?>

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