ceph/src/boost/libs/math/example/error_policy_example.cpp

   1 // example_policy_handling.cpp
   2
   3 // Copyright Paul A. Bristow 2007, 2010.
   4 // Copyright John Maddock 2007.
   5
   6 // Use, modification and distribution are subject to the
   7 // Boost Software License, Version 1.0.
   8 // (See accompanying file LICENSE_1_0.txt
   9 // or copy at http://www.boost.org/LICENSE_1_0.txt)
  10
  11 // See error_handling_example.cpp for use of
  12 // macro definition to change policy for
  13 // domain_error - negative degrees of freedom argument
  14 // for student's t distribution CDF,
  15 // and catching the exception.
  16
  17 // See error_handling_policies.cpp for more examples.
  18
  19 // Boost
  20 #include <boost/math/distributions/students_t.hpp>
  21 using boost::math::students_t_distribution;  // Probability of students_t(df, t).
  22 using boost::math::students_t;  // Probability of students_t(df, t) convenience typedef for double.
  23
  24 using boost::math::policies::policy;
  25 using boost::math::policies::domain_error;
  26 using boost::math::policies::ignore_error;
  27
  28 // std
  29 #include <iostream>
  30    using std::cout;
  31    using std::endl;
  32
  33 #include <stdexcept>
  34
  35
  36 // Define a (bad?) policy to ignore domain errors ('bad' arguments):
  37 typedef policy<
  38       domain_error<ignore_error>
  39       > my_policy;
  40
  41 // Define my_students_t distribution with this different domain error policy:
  42 typedef students_t_distribution<double, my_policy> my_students_t;
  43
  44 int main()
  45 {  // Example of error handling of bad argument(s) to a distribution.
  46   cout << "Example error handling using Student's t function. " << endl;
  47
  48   double degrees_of_freedom = -1; double t = -1.; // Two 'bad' arguments!
  49
  50   try
  51   {
  52     cout << "Probability of ignore_error Student's t is "
  53       << cdf(my_students_t(degrees_of_freedom), t) << endl;
  54     cout << "Probability of default error policy Student's t is " << endl;
  55     // By contrast the students_t distribution default domain error policy is to throw,
  56     cout << cdf(students_t(-1), -1) << endl;  // so this will throw.
  57 /*`
  58     Message from thrown exception was:
  59    Error in function boost::math::students_t_distribution<double>::students_t_distribution:
  60    Degrees of freedom argument is -1, but must be > 0 !
  61 */
  62
  63     // We could also define a 'custom' distribution
  64     // with an "ignore overflow error policy" in a single statement:
  65     using boost::math::policies::overflow_error;
  66     students_t_distribution<double, policy<overflow_error<ignore_error> > > students_t_no_throw(-1);
  67
  68   }
  69   catch(const std::exception& e)
  70   {
  71     std::cout <<
  72       "\n""Message from thrown exception was:\n   " << e.what() << std::endl;
  73   }
  74
  75   return 0;
  76 } // int main()
  77
  78 /*
  79
  80 Output:
  81
  82    error_policy_example.cpp
  83   Generating code
  84   Finished generating code
  85   error_policy_example.vcxproj -> J:\Cpp\MathToolkit\test\Math_test\Release\error_policy_example.exe
  86   Example error handling using Student's t function.
  87   Probability of ignore_error Student's t is 1.#QNAN
  88   Probability of default error policy Student's t is
  89
  90   Message from thrown exception was:
  91      Error in function boost::math::students_t_distribution<double>::students_t_distribution: Degrees of freedom argument is -1, but must be > 0 !
  92
  93 */