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- // Copyright Paul Bristow 2013.
- // Copyright John Maddock 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)
- /*! \brief Examples of using the enhanced math constants.
- \details This allows for access to constants via functions like @c pi(),
- and also via namespaces, @c using @c namespace boost::math::double_constants;
- called simply @c pi.
- */
- #include <boost/math/constants/constants.hpp>
- #include <iostream>
- using std::cout;
- using std::endl;
- #include <limits>
- using std::numeric_limits;
- /*! \brief Examples of a template function using constants.
- \details This example shows using of constants from function calls like @c pi(),
- rather than the 'cute' plain @c pi use in non-template applications.
- \tparam Real radius parameter that can be a built-in like float, double,
- or a user-defined type like multiprecision.
- \returns Area = pi * radius ^ 2
- */
- //[math_constants_eg1
- template<class Real>
- Real area(Real r)
- {
- using namespace boost::math::constants;
- return pi<Real>() * r * r;
- }
- //] [/math_constants_eg1]
- int main()
- {
- { // Boost.Math constants using function calls like pi().
- // using namespace boost::math::constants;
- using boost::math::constants::pi;
- using boost::math::constants::one_div_two_pi;
- #ifdef BOOST_NO_CXX11_NUMERIC_LIMITS
- std::size_t max_digits10 = 2 + std::numeric_limits<double>::digits * 3010/10000;
- #else
- std::size_t max_digits10 = std::numeric_limits<double>::max_digits10;
- #endif
- std::cout.precision(max_digits10);
- cout << "double pi = boost::math::double_constants::pi = " << pi<double>() << endl;
- // double pi = boost::math::double_constants::pi = 3.1415926535897931
- double r = 1.234567890123456789;
- double d = pi<double>() * r * r;
- cout << "d = " << d << ", r = " << r << endl;
- float rf = 0.987654321987654321f;
- float pif = boost::math::constants::pi<float>();
- cout << "pidf = boost::math::constants::pi() = " << pif << endl;
- // pidf = boost::math::float_constants::pi = 3.1415927410125732
- //float df = pi * rf * rf; // conversion from 'const double' to 'float', possible loss of data.
- float df = pif * rf * rf;
- cout << "df = " << df << ", rf = " << rf << endl;
- cout << "one_div_two_pi " << one_div_two_pi<double>() << endl;
- using boost::math::constants::one_div_two_pi;
- cout << "one_div_root_two_pi " << one_div_two_pi<double>() << endl;
- }
- { // Boost math new constants using namespace selected values, like pi.
- //using namespace boost::math::float_constants;
- using namespace boost::math::double_constants;
- double my2pi = two_pi; // Uses boost::math::double_constants::two_pi;
- cout << "double my2pi = " << my2pi << endl;
- using boost::math::float_constants::e;
- float my_e = e;
- cout << "float my_e " << my_e << endl;
- double my_pi = boost::math::double_constants::pi;
- cout << "double my_pi = boost::math::double_constants::pi = " << my_pi << endl;
- // If you try to use two namespaces, this may, of course, create ambiguity:
- // it is not too difficult to do this inadvertently.
- using namespace boost::math::float_constants;
- //cout << pi << endl; // error C2872: 'pi' : ambiguous symbol.
- }
- {
- //[math_constants_ambiguity
- // If you use more than one namespace, this will, of course, create ambiguity:
- using namespace boost::math::double_constants;
- using namespace boost::math::constants;
- //double my_pi = pi(); // error C2872: 'pi' : ambiguous symbol
- //double my_pi2 = pi; // Context does not allow for disambiguation of overloaded function
- // It is also possible to create ambiguity inadvertently,
- // perhaps in other peoples code,
- // by making the scope of a namespace declaration wider than necessary,
- // therefore is it prudent to avoid this risk by localising the scope of such definitions.
- //] [/math_constants_ambiguity]
- }
- { // You can, of course, use both methods of access if both are fully qualified, for examples:
- //cout.precision(std::numeric_limits<double>::max_digits10);// Ideally.
- cout.precision(2 + std::numeric_limits<double>::digits * 3010/10000); // If no max_digits10.
- double my_pi1 = boost::math::constants::pi<double>();
- double my_pid = boost::math::double_constants::pi;
- cout << "boost::math::constants::pi<double>() = " << my_pi1 << endl
- << "boost::math::double_constants::pi = " << my_pid << endl;
- // cout.precision(std::numeric_limits<float>::max_digits10); // Ideally.
- cout.precision(2 + std::numeric_limits<double>::digits * 3010/10000); // If no max_digits10.
- float my_pif = boost::math::float_constants::pi;
- cout << "boost::math::float_constants::pi = " << my_pif << endl;
- }
- { // Use with templates
- // \warning it is important to be very careful with the type provided as parameter.
- // For example, naively providing an @b integer instead of a floating-point type can be disastrous.
- // cout << "Area = " << area(2) << endl; // warning : 'return' : conversion from 'double' to 'int', possible loss of data
- // Failure to heed this warning can lead to very wrong answers!
- // Area = 12 !! = 3 * 2 * 2
- //[math_constants_template_integer_type
- //cout << "Area = " << area(2) << endl; // Area = 12!
- cout << "Area = " << area(2.) << endl; // Area = 12.566371
- // You can also avoid this by being explicit about the type of @c area.
- cout << "Area = " << area<double>(2) << endl;
- //] [/math_constants_template_integer_type]
- }
- /*
- {
- using boost::math::constants::pi;
- //double my_pi3 = pi<double>(); // OK
- //double my_pi4 = pi<>(); cannot find template type.
- //double my_pi4 = pi(); // Can't find a function.
- }
- */
- } // int main()
- /*[constants_eq1_output
- Output:
- double pi = boost::math::double_constants::pi = 3.1415926535897931
- d = 4.7882831840285398, r = 1.2345678901234567
- pidf = boost::math::constants::pi() = 3.1415927410125732
- df = 3.0645015239715576, rf = 0.98765432834625244
- one_div_two_pi 0.15915494309189535
- one_div_root_two_pi 0.15915494309189535
- double my2pi = 6.2831853071795862
- float my_e 2.7182817459106445
- double my_pi = boost::math::double_constants::pi = 3.1415926535897931
- boost::math::constants::pi<double>() = 3.1415926535897931
- boost::math::double_constants::pi = 3.1415926535897931
- boost::math::float_constants::pi = 3.1415927410125732
- Area = 12.566370614359172
- Area = 12.566370614359172
- ] [/constants_eq1_output]
- */
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