(PECL stats >= 1.0.0)
stats_dens_normal — Probability density function of the normal distribution
Returns the probability density at x, where the
random variable follows the normal distribution of which the mean is
ave and the standard deviation is
stdev.
xThe value at which the probability density is calculated
aveThe mean of the distribution
stdevThe standard deviation of the distribution
The probability density at x or false for failure.
If you don't have the stats package and can't install it, I have found this to work:
<?php
if (!function_exists('stats_dens_normal')) {
function stats_dens_normal(float $x, float $ave, float $stdev): float
{
$A = $stdev * sqrt(2 * M_PI);
$B = -pow($x - $ave, 2);
$C = 2 * pow($stdev, 2);
return (1 / $A) * pow(M_E, $B / $C);
}
}
?>I'm not certain that I've figured this one out correctly but it should return the value of a (Gaussian) normal distribution of the given properties at the given location.
$x - the X-Value to request
$ave - the 'expected value' (i.e. location of the peak) for the distribution. For most uses this will just be 0.
$stdev - the standard deviation of the distribution. For most uses this will be 1.