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122 lines
3.4 KiB
C++
122 lines
3.4 KiB
C++
// Copyright John Maddock 2007.
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// Copyright Paul A. Bristow 2010
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// Use, modification and distribution are subject to the
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// Boost Software License, Version 1.0. (See accompanying file
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// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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// Note that this file contains quickbook mark-up as well as code
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// and comments, don't change any of the special comment mark-ups!
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#include <iostream>
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using std::cout; using std::endl;
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#include <cerrno> // for ::errno
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//[policy_eg_6
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/*`
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Suppose we want a set of distributions to behave as follows:
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* Return infinity on overflow, rather than throwing an exception.
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* Don't perform any promotion from double to long double internally.
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* Return the closest integer result from the quantiles of discrete
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distributions.
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We'll begin by including the needed header for all the distributions:
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*/
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#include <boost/math/distributions.hpp>
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/*`
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Open up an appropriate namespace, calling it `my_distributions`,
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for our distributions, and define the policy type we want.
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Any policies we don't specify here will inherit the defaults:
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*/
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namespace my_distributions
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{
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using namespace boost::math::policies;
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// using boost::math::policies::errno_on_error; // etc.
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typedef policy<
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// return infinity and set errno rather than throw:
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overflow_error<errno_on_error>,
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// Don't promote double -> long double internally:
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promote_double<false>,
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// Return the closest integer result for discrete quantiles:
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discrete_quantile<integer_round_nearest>
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> my_policy;
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/*`
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All we need do now is invoke the BOOST_MATH_DECLARE_DISTRIBUTIONS
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macro passing the floating point type `double` and policy types `my_policy` as arguments:
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*/
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BOOST_MATH_DECLARE_DISTRIBUTIONS(double, my_policy)
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} // close namespace my_namespace
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/*`
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We now have a set of typedefs defined in namespace my_distributions
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that all look something like this:
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``
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typedef boost::math::normal_distribution<double, my_policy> normal;
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typedef boost::math::cauchy_distribution<double, my_policy> cauchy;
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typedef boost::math::gamma_distribution<double, my_policy> gamma;
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// etc
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``
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So that when we use my_distributions::normal we really end up using
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`boost::math::normal_distribution<double, my_policy>`:
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*/
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int main()
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{
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// Construct distribution with something we know will overflow
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// (using double rather than if promoted to long double):
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my_distributions::normal norm(10, 2);
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errno = 0;
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cout << "Result of quantile(norm, 0) is: "
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<< quantile(norm, 0) << endl; // -infinity.
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cout << "errno = " << errno << endl;
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errno = 0;
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cout << "Result of quantile(norm, 1) is: "
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<< quantile(norm, 1) << endl; // +infinity.
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cout << "errno = " << errno << endl;
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// Now try a discrete distribution.
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my_distributions::binomial binom(20, 0.25);
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cout << "Result of quantile(binom, 0.05) is: "
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<< quantile(binom, 0.05) << endl; // To check we get integer results.
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cout << "Result of quantile(complement(binom, 0.05)) is: "
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<< quantile(complement(binom, 0.05)) << endl;
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}
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/*`
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Which outputs:
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[pre
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Result of quantile(norm, 0) is: -1.#INF
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errno = 34
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Result of quantile(norm, 1) is: 1.#INF
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errno = 34
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Result of quantile(binom, 0.05) is: 1
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Result of quantile(complement(binom, 0.05)) is: 8
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]
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This mechanism is particularly useful when we want to define a
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project-wide policy, and don't want to modify the Boost source
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or set project wide build macros (possibly fragile and easy to forget).
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*/
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//] //[/policy_eg_6]
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