ceph/src/boost/libs/math/example/policy_eg_6.cpp

   1 //  Copyright John Maddock 2007.
   2 //  Copyright Paul A. Bristow 2010
   3 //  Use, modification and distribution are subject to the
   4 //  Boost Software License, Version 1.0. (See accompanying file
   5 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6
   7 // Note that this file contains quickbook mark-up as well as code
   8 // and comments, don't change any of the special comment mark-ups!
   9
  10 #include <iostream>
  11 using std::cout;  using std::endl;
  12 #include <cerrno> // for ::errno
  13
  14 //[policy_eg_6
  15
  16 /*`
  17 Suppose we want a set of distributions to behave as follows:
  18
  19 * Return infinity on overflow, rather than throwing an exception.
  20 * Don't perform any promotion from double to long double internally.
  21 * Return the closest integer result from the quantiles of discrete
  22 distributions.
  23
  24 We'll begin by including the needed header for all the distributions:
  25 */
  26
  27 #include <boost/math/distributions.hpp>
  28
  29 /*`
  30
  31 Open up an appropriate namespace, calling it `my_distributions`,
  32 for our distributions, and define the policy type we want.
  33 Any policies we don't specify here will inherit the defaults:
  34
  35 */
  36
  37 namespace my_distributions
  38 {
  39   using namespace boost::math::policies;
  40   // using boost::math::policies::errno_on_error; // etc.
  41
  42   typedef policy<
  43      // return infinity and set errno rather than throw:
  44      overflow_error<errno_on_error>,
  45      // Don't promote double -> long double internally:
  46      promote_double<false>,
  47      // Return the closest integer result for discrete quantiles:
  48      discrete_quantile<integer_round_nearest>
  49   > my_policy;
  50
  51 /*`
  52
  53 All we need do now is invoke the BOOST_MATH_DECLARE_DISTRIBUTIONS
  54 macro passing the floating point type `double` and policy types `my_policy` as arguments:
  55
  56 */
  57
  58 BOOST_MATH_DECLARE_DISTRIBUTIONS(double, my_policy)
  59
  60 } // close namespace my_namespace
  61
  62 /*`
  63
  64 We now have a set of typedefs defined in namespace my_distributions
  65 that all look something like this:
  66
  67 ``
  68 typedef boost::math::normal_distribution<double, my_policy> normal;
  69 typedef boost::math::cauchy_distribution<double, my_policy> cauchy;
  70 typedef boost::math::gamma_distribution<double, my_policy> gamma;
  71 // etc
  72 ``
  73
  74 So that when we use my_distributions::normal we really end up using
  75 `boost::math::normal_distribution<double, my_policy>`:
  76
  77 */
  78
  79 int main()
  80 {
  81    // Construct distribution with something we know will overflow
  82   // (using double rather than if promoted to long double):
  83    my_distributions::normal norm(10, 2);
  84
  85    errno = 0;
  86    cout << "Result of quantile(norm, 0) is: "
  87       << quantile(norm, 0) << endl; // -infinity.
  88    cout << "errno = " << errno << endl;
  89    errno = 0;
  90    cout << "Result of quantile(norm, 1) is: "
  91       << quantile(norm, 1) << endl; // +infinity.
  92    cout << "errno = " << errno << endl;
  93
  94    // Now try a discrete distribution.
  95    my_distributions::binomial binom(20, 0.25);
  96    cout << "Result of quantile(binom, 0.05) is: "
  97       << quantile(binom, 0.05) << endl; // To check we get integer results.
  98    cout << "Result of quantile(complement(binom, 0.05)) is: "
  99       << quantile(complement(binom, 0.05)) << endl;
 100 }
 101
 102 /*`
 103
 104 Which outputs:
 105
 106 [pre
 107 Result of quantile(norm, 0) is: -1.#INF
 108 errno = 34
 109 Result of quantile(norm, 1) is: 1.#INF
 110 errno = 34
 111 Result of quantile(binom, 0.05) is: 1
 112 Result of quantile(complement(binom, 0.05)) is: 8
 113 ]
 114
 115 This mechanism is particularly useful when we want to define a
 116 project-wide policy, and don't want to modify the Boost source
 117 or set  project wide build macros (possibly fragile and easy to forget).
 118
 119 */
 120 //] //[/policy_eg_6]
 121