stats_standard_deviation

Does anyone have more details on stats_standard_deviation than the
manual provides?
--

Regards,

Jeff Gardner
___________________________

"Contrary to popular belief, Unix is user friendly. It just happens
to be very selective about who its friends are." --Kyle Hearn

Jeff Gardner wrote:

> Does anyone have more details on stats_standard_deviation than the
> manual provides?

Hi Jeff,

The describtion is very bad indeed.

Why use an undocumented (bad documented) function for such a simple thing?
I would write my own implementation in such case.
Calculation the SD is very straightforward.

On the same page on www.php.net you can also find a contribution with a
working example.

[Source]
http://nl2.php.net/manual/en/functio...-deviation.php

function average($array){
$sum = array_sum($array);
$count = count($array);
return $sum/$count;
}

//The average function can be use independantly but the deviation function
uses the average function.

function deviation ($array){

$avg = average($array);
foreach ($array as $value) {
$variance[] = pow($value-$avg, 2);
}
$deviation = sqrt(average($variance));
return $deviation;
}

Regards,
Erwin Moller

Jeff Gardner wrote:
>
> Does anyone have more details on stats_standard_deviation
> than the manual provides?

Why bother? Standard deviation is a really simple thing to
compute:

function stat_mean ($data) {
return (array_sum($data) / count($data));
}

function stat_var ($data) {
$n = count ($data);
$mean = stat_mean ($data);
$sum = 0;
foreach ($data as $element) {
$sum += pow (($element - $mean), 2);
}
return ($sum / ($n - 1));
}

function stat_stdev ($data) {
return sqrt (stat_var($data));
}

Cheers,
NC