Re: Discrete random with given distribution ?

[Wes Groleau <wesgroleau@despammed.com>]

> >My first method must be determined before compile time
> >(Actually, there is a way to approximate it at run-time,
> >but it is a bit clumsy)
> 
> >If the probabilities are to be determined at runtime,
> >my second method will work, if you
>   Why not just use your second method (summing probabilities till you
> hit a certain level) to calculate, at run time, the population of
> a lookup table, then use the first method to speedily index into
> it to pick a random element.

That's what I meant by a bit clumsy.  And it could be a fairly
large lookup table, depending on how accurate you try to be.

Size := 10 ** Digits_Of_Accuracy;

Lookup : array ( 1 .. Size ) of Discrete_Things;

Index := Lookup'First;
for I in Discrete_Things loop
   Span := Integer (Probability (I));
   for J in Index .. Index + Span - 1 loop
      Lookup (J) := I;
   end loop;
   Index := Index + Span;
end loop;

Hmmm, that's not as clumsy as I thought it would be.  :-)

-- 
Wes Groleau
http://freepages.rootsweb.com/~wgroleau