# Re: [Boost-bugs] [Boost C++ Libraries] #9966: exponential_distribution returns negative zero

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #9966: exponential_distribution returns negative zero
Date: 2015-02-27 15:48:58

#9966: exponential_distribution returns negative zero
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Reporter: mazzamuto@â€¦ | Owner: no-maintainer
Type: Bugs | Status: new
Milestone: To Be Determined | Component: random
Version: Boost 1.48.0 | Severity: Problem
Resolution: | Keywords:
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Comment (by steven_watanabe):

> I agree that the problem is not with the sign. Indeed I recognize that
the documentation states: The domain of the random variable is [0, +Inf].

Which documentation? I don't see any such statement in
the Boost.Random docs.

> This causes another problem with the upper limit +Inf being documented
as included. For example, this code should produce the minimum and maximum
values obtainable from exponential_distribution with lambda=1:

An exponential_distribution should never produce +Inf. Theoretically,
lim_{x->\inf} p(x) = 0, so while the values can be arbitrarily large, the
distribution should never produce infinity. We have to approximate the
distribution, because floating point cannot represent every real number,
but adding +Inf as a possible output would severely bias the distribution
(i.e. the mean would become +Inf). I can't think of any circumstances
where I would want it to return +Inf.

```--
Ticket URL: <https://svn.boost.org/trac/boost/ticket/9966#comment:5>
Boost C++ Libraries <http://www.boost.org/>
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```

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