Re: [Boost-bugs] [Boost C++ Libraries] #920: Proposed extension to random library

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #920: Proposed extension to random library
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2008-02-09 01:11:41

#920: Proposed extension to random library
-------------------------------+--------------------------------------------
  Reporter:  nobody            |       Owner:  no-maintainer
      Type:  Feature Requests  |      Status:  new          
 Milestone:                    |   Component:  random       
   Version:  None              |    Severity:  Showstopper  
Resolution:  None              |    Keywords:               
-------------------------------+--------------------------------------------
Changes (by marshall):

  * owner:  jmaurer => no-maintainer
  * status:  assigned => new
  * severity:  => Showstopper

Old description:

> {{{
> I suggest adding the following utility function to
> the random library (with perhaps a name change):
>
> // PURPOSE: Sample from a set of N values given the
> // sequence p[1], p[1] + p[2], p[1] + p[2] + p[3], ...
> // of cumulative probabilities.
> //
> // REQUIRE:
> // - Type Incrementer supports the pre-increment
> //   operation and equality comparison.  Typically,
> //   Incrementer will be an integral type or a
> //   forward iterator.
> // - Pre-incrementing i some finite number of times
> //   -- say, N -- makes it equal to iend.
> // - cumprob_it "points" at a nondecreasing sequence
> //   of at least N nonnegative numbers, with the N-th
> //   value in the sequence being equal to 1.0.
> //
> // RETURNS:
> // A random value in the interval [i, iend), with
> // cumprob_it defining the sequence of cumulative
> // probabilities.
>
> template <typename InputIterator,
>           typename Incrementer,
>           class UniformRandomNumberGenerator>
> Incrementer
> rand(Incrementer i, Incrementer iend,
>      InputIterator cumprob_it,
>      UniformRandomNumberGenerator & rng)
> {
>   typedef
>     std::iterator_traits<InputIterator>::value_type
>     number_t;
>   uniform_01<UniformRandomNumberGenerator, number_t>
>     urng(rng);
>   number_t p = urng();
>   for ( ; p >= *cumprob_it; ++cumprob_t) {
>     ++i;
>     assert(!(i == iend));
>   }
>   return i;
> }
>
> -- Kevin S. Van Horn (Kevin_VanHorn_at_[hidden])
> }}}

New description:

 {{{
 I suggest adding the following utility function to
 the random library (with perhaps a name change):

 // PURPOSE: Sample from a set of N values given the
 // sequence p[1], p[1] + p[2], p[1] + p[2] + p[3], ...
 // of cumulative probabilities.
 //
 // REQUIRE:
 // - Type Incrementer supports the pre-increment
 //   operation and equality comparison.  Typically,
 //   Incrementer will be an integral type or a
 //   forward iterator.
 // - Pre-incrementing i some finite number of times
 //   -- say, N -- makes it equal to iend.
 // - cumprob_it "points" at a nondecreasing sequence
 //   of at least N nonnegative numbers, with the N-th
 //   value in the sequence being equal to 1.0.
 //
 // RETURNS:
 // A random value in the interval [i, iend), with
 // cumprob_it defining the sequence of cumulative
 // probabilities.

 template <typename InputIterator,
           typename Incrementer,
           class UniformRandomNumberGenerator>
 Incrementer
 rand(Incrementer i, Incrementer iend,
      InputIterator cumprob_it,
      UniformRandomNumberGenerator & rng)
 {
   typedef
     std::iterator_traits<InputIterator>::value_type
     number_t;
   uniform_01<UniformRandomNumberGenerator, number_t>
     urng(rng);
   number_t p = urng();
   for ( ; p >= *cumprob_it; ++cumprob_t) {
     ++i;
     assert(!(i == iend));
   }
   return i;
 }

 -- Kevin S. Van Horn (Kevin_VanHorn_at_[hidden])
 }}}

-- 
Ticket URL: <http://svn.boost.org/trac/boost/ticket/920#comment:2>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.