[Boost-bugs] [Boost C++ Libraries] #10110: boost::random::negative_binomial_distribution unnecessary restriction to IntType for parameter k

Subject: [Boost-bugs] [Boost C++ Libraries] #10110: boost::random::negative_binomial_distribution unnecessary restriction to IntType for parameter k
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-06-10 20:23:13

#10110: boost::random::negative_binomial_distribution unnecessary restriction to
IntType for parameter k
-------------------------------------------------+-------------------------
 Reporter:  Maximilian Kleinert                  |      Owner:  no-
  <kleinert.max@…>                               |  maintainer
     Type:  Bugs                                 |     Status:  new
Milestone:  To Be Determined                     |  Component:  random
  Version:  Boost 1.55.0                         |   Severity:  Problem
 Keywords:  random, negative binomial            |
  distribution                                   |
-------------------------------------------------+-------------------------
 Hi.

 In the implementation of boost::random::negative_binomial_distribution
 there is an unnecessary restriction to IntType for parameter k.

 A double parameter k will be casted to integer resulting in a different
 distribution than desired. If one compiles with -Wconversion a warning is
 given:
 warning: conversion to ‘int’ from ‘double’ may alter its value
 [-Wconversion]
 see attached example_file.
 This can lead to unwanted realization of a negative binomial distribution
 for non integer parameters k.

 Further there are no assertion checks on the parameters in instantiating a
 boost::random::negative_binomial_distribution object. These assertions are
 checked during the sampling process via boost::random::gamma_distribution.
 There (and in general for negative binomial distribution) the parameter k
 must be strictly greater than zero and not as mentioned in the
 documentation "Requires: k >=0".

 This can easily be extended by changing IntType to RealType in 5
 occurrences regarding the parameter k.

 Thank you,
 Max

 P.S.: I compiled the example file with:
 g++ -Wconversion -o negbin_test -std=c++11 negbin_test.cpp

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10110>
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