Standard deviation generator

[Floydian]

The code snippet below will generate a random number within a certain distance from zero. $variance is a percentage, with 100% being equal to a distance of -1 to 1, and 50% being equal to a distance of -0.5 to 0.5.

 

/**
* Generates a random number within a given range.
*
* @param float $variance
* A range above and below zero.
* @return float
* A number greater than or less than zero within a range defined by $varience.
*/
function deviation($variance) {
return (mt_rand(0, $variance * 200) - $variance * 100) *0.0001;
}

 

The value returned can be then be multiplied against another value and added to itself. This can be useful if one needs to take crime exp and randomize it:

 

$crime_exp = 100;
$variance = deviation(5);
$crime_exp = $crime_exp + $crime_exp * $variance;

 

Sample code:

 

<?php
function deviation($variance) {
return (mt_rand(0, $variance * 200) - $variance * 100) *0.0001;
}


for ($x = 1; $x <= 30; $x++ ) {
$crime_exp = 100;
$variance = deviation(5);
$crime_exp = $crime_exp + $crime_exp * $variance;
echo $crime_exp; echo "\n";
}

 

Sample output:

 

104.12
99.79
95.94
101.6
99.02
104.06
95.01
95.56
95.04
97.4
101.99
95.35
95.62
104.19
100.49
100.25
98.19
101.89
98.05
104.86
99.58
99.24
104
101.17
104.99
98.42
100
95.33
95.82
103.02