PHP - Stats CDF Chisquare() Function

Definition and Usage

The stats_cdf_chisquare() function calculates any one parameter of the chi-square distribution given values for the others.

Syntax

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

Parameters

Sr.No	Parameter	Description
1	par1	The first parameter
2	par2	The second parameter
3	which	The flag to determine what to be calculated

Return Values

This function returns the cumulative distribution function, its inverse, or one of its parameters, of the chi-square distribution. The kind of the return value and parameters (par1 and par2) are 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.
k denotes the degree of freedom of the chi-square distribution.

which	Return value	par1	par2
1	CDF	x	k
2	x	CDF	k
3	k	x	CDF

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 (X, DF).

P is the the integral from 0 to X of the chi-square distribution. Input range: [0, 1] .
X is the upper limit of integration of the non-central chi-square distribution. Input range: [0, +infinity].
DF is Degrees of freedom of the chi-square distribution. Input range: (0, +infinity)..

<?php
   // which = 1 : calculate P from (X, DF)
   var_dump(round(stats_cdf_chisquare(1, 2, 1), 6));
?>

Output

This will produce following result −

float(0.393469)

Example

In the following example when which=2, calculate X from (P, DF).

P is the the integral from 0 to X of the chi-square distribution. Input range: [0, 1] .
X is the upper limit of integration of the non-central chi-square distribution. Input range: [0, +infinity].
DF is Degrees of freedom of the chi-square distribution. Input range: (0, +infinity).

<?php
   // which = 2 : calculate X from (P, DF)
   var_dump(round(stats_cdf_chisquare(0.393469340, 2, 2), 6));
?>

Output

This will produce following result −

float(1)

Example

In the following example when which=3, calculate MEAN from (P, X, SD).

P is the the integral from 0 to X of the chi-square distribution. Input range: [0, 1] .
X is the upper limit of integration of the non-central chi-square distribution. Input range: [0, +infinity].
DF is Degrees of freedom of the chi-square distribution. Input range: (0, +infinity).

<?php
   // which = 3 : calculate DF from (P, X)
   var_dump(round(stats_cdf_chisquare(0.393469340, 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_chisquare(1, 2, 0)); // which < 1
?>

Output

This will produce following result and a warning in logs PHP Warning: stats_cdf_chisquare(): 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_chisquare(1, 2, 4));  // which > 3
?>

Output

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

bool(false)