id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
9126	Logistic distribution pdf() and cdf(complement()) fail to catch invalid scale and location parameters	Paul McClellan <paulm@…>	Paul A. Bristow	"This issue is related to '''Ticket #9042'''

In '''boost/math/distributions/logistic.hpp''':

{{{
    template <class RealType, class Policy>
    inline RealType pdf(const logistic_distribution<RealType, Policy>& dist, const RealType& x)
    {
       RealType scale = dist.scale();
       RealType location = dist.location();

       static const char* function = ""boost::math::pdf(const logistic_distribution<%1%>&, %1%)"";
       if((boost::math::isinf)(x))
       {
          return 0; // pdf + and - infinity is zero.
       }

       RealType result = 0;
       if(false == detail::check_scale(function, scale , &result, Policy()))
       {
          return result;
       }
       if(false == detail::check_location(function, location, &result, Policy()))
       {
          return result;
       }
       if(false == detail::check_x(function, x, &result, Policy()))
       {
          return result;
       }

       BOOST_MATH_STD_USING
       RealType exp_term = (location - x) / scale;
       if(fabs(exp_term) > tools::log_max_value<RealType>())
          return 0;
       exp_term = exp(exp_term);
       if((exp_term * scale > 1) && (exp_term > tools::max_value<RealType>() / (scale * exp_term)))
          return 1 / (scale * exp_term);
       return (exp_term) / (scale * (1 + exp_term) * (1 + exp_term));
    } 
}}}

The test if((boost::math::isinf)(x)) occurs before check_scale() or check_location() is called, returning  0 for infinite x, even if scale or location are invalid.

The calls to check_scale() and check_location() should be moved up just before the test if((boost::math::isinf)(x)). 

See, for example, how the tests are ordered here: 

{{{
    template <class RealType, class Policy>
    inline RealType cdf(const logistic_distribution<RealType, Policy>& dist, const RealType& x)
    {
       RealType scale = dist.scale();
       RealType location = dist.location();
       RealType result = 0; // of checks.
       static const char* function = ""boost::math::cdf(const logistic_distribution<%1%>&, %1%)"";
       if(false == detail::check_scale(function, scale, &result, Policy()))
       {
          return result;
       }
       if(false == detail::check_location(function, location, &result, Policy()))
       {
          return result;
       }

       if((boost::math::isinf)(x))
       {
          if(x < 0) return 0; // -infinity
          return 1; // + infinity
       }

       if(false == detail::check_x(function, x, &result, Policy()))
       {
          return result;
       }
       BOOST_MATH_STD_USING
       RealType power = (location - x) / scale;
       if(power > tools::log_max_value<RealType>())
          return 0;
       if(power < -tools::log_max_value<RealType>())
          return 1;
       return 1 / (1 + exp(power)); 
    } 
 }}}

The same issue exists with the complementary cdf:

{{{
    template <class RealType, class Policy>
    inline RealType cdf(const complemented2_type<logistic_distribution<RealType, Policy>, RealType>& c)
    {
       BOOST_MATH_STD_USING
       RealType location = c.dist.location();
       RealType scale = c.dist.scale();
       RealType x = c.param;
       static const char* function = ""boost::math::cdf(const complement(logistic_distribution<%1%>&), %1%)"";

       if((boost::math::isinf)(x))
       {
          if(x < 0) return 1; // cdf complement -infinity is unity.
          return 0; // cdf complement +infinity is zero
       }
       RealType result = 0;
       if(false == detail::check_scale(function, scale, &result, Policy()))
          return result;
       if(false == detail::check_location(function, location, &result, Policy()))
          return result;
       if(false == detail::check_x(function, x, &result, Policy()))
          return result;
       RealType power = (x - location) / scale;
       if(power > tools::log_max_value<RealType>())
          return 0;
       if(power < -tools::log_max_value<RealType>())
          return 1;
       return 1 / (1 + exp(power)); 
    } 
}}}"	Bugs	closed	Boost 1.55.0	math	Boost 1.54.0	Problem	fixed