Re: Random number generator that returns numbers from

I have an XQuery function that does it. It depends on an underlying 
function (here rand:uniform) to give uniform numbers in [0,1].B  Most 
"random" functions will give you uniformly distributed random numbers; 
if your platform doesn't have one, you'll have to concoct your own 
pseudo-random function

This is the polar variant of the Box-Muller algorithm

(:
  : normal()
  : Return random normally distributed data.
  :
  : $mean: Mean of range of values
  : $std: Standard deviation of range of values
  :)
declare function rand:normal(
   $mean as xs:double,
   $std as xs:double
) as xs:double
{
   $mean + rand:gauss() * $std
};

(:
  : gauss()
  : Return random normally distributed data between 0 and 1
  : A service function used by normal()
  :)
declare %private function rand:gauss() as xs:double
{
   let $u as xs:double := 2 * rand:uniform(0,1) - 1
   let $v as xs:double := 2 * rand:uniform(0,1) - 1
   let $r := $u * $u + $v * $v
   return (
     if ($r = 0 or $r >= 1) then rand:gauss()
     else (
       let $c as xs:double := math:sqrt(-2 * math:log($r) div $r)
       return $u * $c
     )
   )
};


On 5/31/20 10:37 AM, Roger L Costello costello@xxxxxxxxx wrote:
> Hi Folks,
>
> I need a random number generator that returns numbers from a normal probability distribution, centered around zero, and with standard deviation that can be specified. Has anyone created such a thing?
>
> I am using XSLT/XPath 2.0
>
> /Roger