// Copyright John Maddock 2007. // Use, modification and distribution are subject to the // Boost Software License, Version 1.0. (See accompanying file // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) // Note that this file contains quickbook mark-up as well as code // and comments, don't change any of the special comment mark-ups! #include <iostream> //[policy_eg_6 /*` Suppose we want a set of distributions to behave as follows: * Return infinity on overflow, rather than throwing an exception. * Don't perform any promotion from double to long double internally. * Return the closest integer result from the quantiles of discrete distributions. We'll begin by including the needed header: */ #include <boost/math/distributions.hpp> /*` Open up an appropriate namespace for our distributions, and define the policy type we want. Any policies we don't specify here will inherit the defaults: */ namespace my_distributions{ using namespace boost::math::policies; typedef policy< // return infinity and set errno rather than throw: overflow_error<errno_on_error>, // Don't promote double -> long double internally: promote_double<false>, // Return the closest integer result for discrete quantiles: discrete_quantile<integer_round_nearest> > my_policy; /*` All we need do now is invoke the BOOST_MATH_DECLARE_DISTRIBUTIONS macro passing the floating point and policy types as arguments: */ BOOST_MATH_DECLARE_DISTRIBUTIONS(double, my_policy) } // close namespace my_namespace /*` We now have a set of typedefs defined in namespace my_namespace that all look something like this: `` typedef boost::math::normal_distribution<double, my_policy> normal; typedef boost::math::cauchy_distribution<double, my_policy> cauchy; typedef boost::math::gamma_distribution<double, my_policy> gamma; // etc `` So that when we use my_namespace::normal we really end up using `boost::math::normal_distribution<double, my_policy>`: */ int main() { // // Start with something we know will overflow: // my_distributions::normal norm(10, 2); errno = 0; std::cout << "Result of quantile(norm, 0) is: " << quantile(norm, 0) << std::endl; std::cout << "errno = " << errno << std::endl; errno = 0; std::cout << "Result of quantile(norm, 1) is: " << quantile(norm, 1) << std::endl; std::cout << "errno = " << errno << std::endl; // // Now try a discrete distribution: // my_distributions::binomial binom(20, 0.25); std::cout << "Result of quantile(binom, 0.05) is: " << quantile(binom, 0.05) << std::endl; std::cout << "Result of quantile(complement(binom, 0.05)) is: " << quantile(complement(binom, 0.05)) << std::endl; } /*` Which outputs: [pre Result of quantile(norm, 0) is: -1.#INF errno = 34 Result of quantile(norm, 1) is: 1.#INF errno = 34 Result of quantile(binom, 0.05) is: 1 Result of quantile(complement(binom, 0.05)) is: 8 ] This mechanism is particularly useful when we want to define a project-wide policy, and don't want to modify the Boost source or set - possibly fragile and easy to forget - project wide build macros. */ //] ends quickbook imported section