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// Copyright John Maddock 2007.
// Copyright Paul A. Bristow 2010
// 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>
using std::cout; using std::endl;
#include <cerrno> // for ::errno
//[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 for all the distributions:
*/
#include <boost/math/distributions.hpp>
/*`
Open up an appropriate namespace, calling it `my_distributions`,
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;
// using boost::math::policies::errno_on_error; // etc.
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 type `double` and policy types `my_policy` as arguments:
*/
BOOST_MATH_DECLARE_DISTRIBUTIONS(double, my_policy)
} // close namespace my_namespace
/*`
We now have a set of typedefs defined in namespace my_distributions
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_distributions::normal we really end up using
`boost::math::normal_distribution<double, my_policy>`:
*/
int main()
{
// Construct distribution with something we know will overflow
// (using double rather than if promoted to long double):
my_distributions::normal norm(10, 2);
errno = 0;
cout << "Result of quantile(norm, 0) is: "
<< quantile(norm, 0) << endl; // -infinity.
cout << "errno = " << errno << endl;
errno = 0;
cout << "Result of quantile(norm, 1) is: "
<< quantile(norm, 1) << endl; // +infinity.
cout << "errno = " << errno << endl;
// Now try a discrete distribution.
my_distributions::binomial binom(20, 0.25);
cout << "Result of quantile(binom, 0.05) is: "
<< quantile(binom, 0.05) << endl; // To check we get integer results.
cout << "Result of quantile(complement(binom, 0.05)) is: "
<< quantile(complement(binom, 0.05)) << 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 project wide build macros (possibly fragile and easy to forget).
*/
//] //[/policy_eg_6]
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