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PHP - Stats Dens PMF Negative Binomial() Function



Definition and Usage

The stats_dens_pmf_negative_binomial() function is a probability density function of negative binomial distribution.

Syntax

  float stats_dens_pmf_negative_binomial( float $x, float $n, float $pi )

Parameters

Sr.No Parameter Description
1

x

The value at which the probability mass is calculated

2

n

The number of the success of the distribution

3

pi

The success rate of the distribution

Return Values

The stats_dens_pmf_negative_binomial() function can return the probability density at x where the random variable can follow the negative binomial distribution in which the number of success is n, and the success rate is pi. This function can return false on failure.

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, we compute probability mass at each x.

<?php
   // check for each x
   foreach (range(0, 3) as $x) {
      var_dump(stats_dens_pmf_negative_binomial($x, 2, 0.4));
      echo "<br>";
   }
?>

Output

This will produce following result −

  float(0.16)
  float(0.192)
  float(0.1728)
  float(0.13824)

Example

In the following example, we compute probability mass for each n.

<?php
   // check for each n
   foreach (range(0, 3) as $n) {
      var_dump(stats_dens_pmf_negative_binomial(1, $n, 0.4));
      echo "<br>";
   }
?>

Output

This will produce following result −

  float(0)
  float(0.24)
  float(0.192)
  float(0.1152)

Example

In the following example, we compute probability mass for each pi.

<?php
   // check for each pi
   foreach (range(0, 1, 0.2) as $pi) {
      var_dump(stats_dens_pmf_negative_binomial(1, 2, $pi));
      echo "<br>";
   }
?>

Output

This will produce following result −

  float(0)
  float(0.064)
  float(0.192)
  float(0.288)
  float(0.256)
  float(0)

Example

Following is an error case. In the following example, we pass n == 0 and pi == 0. A warning is displayed in logs.

<?php
   // error cases
   var_dump(stats_dens_pmf_negative_binomial(1, 0, 0));    // n == 0 and pi == 0
?>

Output

This will produce following result and a warning in logs PHP Warning: stats_dens_pmf_negative_binomial(): Params leading to pow(0, 0). x: 1.000000E+0 n: 0.000000E+0 pi: 0.000000E+0

bool(false)

Example

Following is an error case. In the following example, we pass x == 0 and pi == 1. A warning is displayed in logs.

<?php
   // error cases
   var_dump(stats_dens_pmf_negative_binomial(0, 2, 1));    // x == 0 and pi == 1
?>

Output

This will produce following result and a warning in logs PHP Warning: stats_dens_pmf_negative_binomial(): Params leading to pow(0, 0). x: 0.000000E+0 n: 2.000000E+0 pi: 1.000000E+0

bool(false)
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