From CodeCodex


$min_val = 3;
$max_val = 20;
$average_val = 5;

$loops = 0;

while ($loops < 100) {
	$total += exprand($min_val, $max_val, $average_val);
	$loops ++;

$average = $total/$loops;
echo '<br>';
echo gettype($total);
echo "<br> $total <br> $loops <br>";
echo $average;

//exponentially weighted random number generator
//generates random numbers throught the base formula
//f(x)=x^a where x is a random number and a is the weight
//function imputs are $min, $max, and $average
//function returns random float between $min and $max
//if run multiple times the average should be near $average
function exprand($min, $max, $average) {
	//the origional exprand didn't accept $min
	//the next 2 lines and the second $resault line add $min functionality
	$max -=$min;
	$average -=$min;
	//calculating exponent
	$exp = ($max/$average)-1;
	//calculating max value for mt_rand
	$maxrand = pow($max,(1/$exp));
	//mt_rand returns integers
	//rounding errors were causing major problems
	//next 3 lines of code generate a random number with accuracy to the millionth
	$maxrand *= 1000000;
	$rand = mt_rand(0,$maxrand);
	$rand /= 1000000;
	//applying curve to $rand
	$resault = pow($rand,$exp);
	//add $min back in
	$resault += $min;
	return $resault;