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From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: Discrete random with given distribution ?
References: <3D0F8880.2668FB86@despammed.com>
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type ps is delta 0.001 range 0.0 .. 1000.0;
for ps'small use 0.001;
> > While a programmer would, of course, recognize the problem when he wrote
> > "1.0/1024.0" and knew he was dealing with 3 digit accuracy, the problem
> > could easily creep in if the Probability array was calculated at run time.
> ... at how simple it _seemed_ to be when I actually wrote it out.
  I think all you need is
  type Probability_Type is delta 0.001 range 0.0 .. 1000.0;
  for Probability_Type'small use 0.001;
  ...
  -- add all the Probability(I) and then divide them by their sum
  -- to guarantee they all add to 1.0 even after rounding to 3 digits.
In this example, of course, 1.0/1024.0 => 0.0 and the last Discrete_Type
is chosen 100% of the time, which may or may not be desirable behavior.