PHP - Stats CDF Poisson() Function

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Definition and Usage

The stats_cdf_poisson() function can calculate any one parameter of Poisson distribution given values for the others.

Syntax

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

Parameters

Return Values

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

Return value and parameters

The following table lists the return value and parameters by which.

• CDF denotes cumulative distribution function.

• x denotes the value of the random variable.

• lambda denotes the parameter of the Poisson distribution.

Dependencies

This function was first introduced in statistics extension (PHP 4.0.0 and PEAR 1.4.0). We have used latest release of stats-2.0.3 (PHP 7.0.0 or newer and PEAR 1.4.0 or newer) for this tutorial.

Example

In the following example when which=1, calculate P from (S, XLAM).

• P is the cumulation from 0 to S of the poisson density. Input range: [0,1].

• S is the upper limit of cumulation of the Poisson.

• XLAM is the Mean of the Poisson distribution.

<?php
   // which = 1 : calculate P from (S, XLAM)
   var_dump(round(stats_cdf_poisson(1, 2, 1), 6));
?>

Output

This will produce following result −

float(0.406006)

Example

In the following example when which=2, calculate A from (P, XLAM).

• P is the cumulation from 0 to S of the poisson density. Input range: [0,1].

• S is the upper limit of cumulation of the Poisson.

• XLAM is the Mean of the Poisson distribution.

<?php
   // which = 2 : calculate A from (P, XLAM)
   var_dump(round(stats_cdf_poisson(0.40600585, 2, 2), 6));
?>

Output

This will produce following result −

float(1)

Example

In the following example when which=3, calculate XLAM from (P, S).

• P is the cumulation from 0 to S of the poisson density. Input range: [0,1].

• S is the upper limit of cumulation of the Poisson.

• XLAM is the Mean of the Poisson distribution.

<?php
   // which = 3 : calculate XLAM from (P, S)
   var_dump(round(stats_cdf_poisson(0.40600585, 1, 3), 6));
?>

Output

This will produce following result −

float(2)

Example

Following is an error case. In the following example which<1, warning is displayed in logs.

<?php
   var_dump(stats_cdf_poisson(1, 2, 0));       // which < 1
?>

Output

This will produce following result and a warning in logs PHP Warning: stats_cdf_poisson(): Third parameter should be in the 1..3 range

bool(false)

Example

Following is an error case. In the following example which>3, warning is displayed in logs.

<?php
   var_dump(stats_cdf_poisson(1, 2, 4));       // which > 3
?>

Output

This will produce following result and a warning in logs PHP Warning: stats_cdf_poisson(): Third parameter should be in the 1..3 range

bool(false)