libs/units/example/lambda.cpp
// Boost.Units - A C++ library for zero-overhead dimensional analysis and // unit/quantity manipulation and conversion // // Copyright (C) 2003-2008 Matthias Christian Schabel // Copyright (C) 2008 Steven Watanabe // // Distributed under 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) // $Id: lambda.cpp 27 2008-06-16 14:50:58Z maehne $ //////////////////////////////////////////////////////////////////////// /// /// \file lambda.cpp /// /// \brief Example demonstrating the usage of Boost.Units' quantity, /// unit, and absolute types in functors created with the /// Boost.Lambda library and stored in Boost.Function objects. /// /// \author Torsten Maehne /// \date 2008-06-04 /// /// A mechanical, electrical, geometrical, and thermal example /// demonstrate how to use Boost.Units' quantity, unit, and absolute /// types in lambda expressions. The resulting functors can be stored /// in boost::function objects. It is also shown how to work around a /// limitation of Boost.Lambda's bind() to help it to find the correct /// overloaded function by specifying its signature with a /// static_cast. /// //////////////////////////////////////////////////////////////////////// #include <iostream> #include <boost/function.hpp> #include <boost/units/io.hpp> #include <boost/units/cmath.hpp> #include <boost/units/pow.hpp> #include <boost/units/systems/si.hpp> #include <boost/units/absolute.hpp> // Include boost/units/lambda.hpp instead of boost/lambda/lambda.hpp // for a convenient usage of Boost.Units' quantity, unit, and absolute // types in lambda expressions. The header augments Boost.Lambda's // return type detuction system to recognize the new types so that not // for each arithmetic operation the return type needs to be // explicitely specified. #include <boost/units/lambda.hpp> #include <boost/lambda/bind.hpp> static const double pi = 3.14159265358979323846; //[lambda_snippet_1 int main(int argc, char **argv) { using namespace std; namespace bl = boost::lambda; namespace bu = boost::units; namespace si = boost::units::si; //////////////////////////////////////////////////////////////////////// // Mechanical example: linear accelerated movement //////////////////////////////////////////////////////////////////////// // Initial condition variables for acceleration, speed, and displacement bu::quantity<si::acceleration> a = 2.0 * si::meters_per_second_squared; bu::quantity<si::velocity> v = 1.0 * si::meters_per_second; bu::quantity<si::length> s0 = 0.5 * si::meter; // Displacement over time boost::function<bu::quantity<si::length> (bu::quantity<si::time>) > s = 0.5 * bl::var(a) * bl::_1 * bl::_1 + bl::var(v) * bl::_1 + bl::var(s0); cout << "Linear accelerated movement:" << endl << "a = " << a << ", v = " << v << ", s0 = " << s0 << endl << "s(1.0 * si::second) = " << s(1.0 * si::second) << endl << endl; // Change initial conditions a = 1.0 * si::meters_per_second_squared; v = 2.0 * si::meters_per_second; s0 = -1.5 * si::meter; cout << "a = " << a << ", v = " << v << ", s0 = " << s0 << endl << "s(1.0 * si::second) = " << s(1.0 * si::second) << endl << endl; //////////////////////////////////////////////////////////////////////// // Electrical example: oscillating current //////////////////////////////////////////////////////////////////////// // Constants for the current amplitude, frequency, and offset current const bu::quantity<si::current> iamp = 1.5 * si::ampere; const bu::quantity<si::frequency> f = 1.0e3 * si::hertz; const bu::quantity<si::current> i0 = 0.5 * si::ampere; // The invocation of the sin function needs to be postponed using // bind to specify the oscillation function. A lengthy static_cast // to the function pointer referencing boost::units::sin() is needed // to avoid an "unresolved overloaded function type" error. boost::function<bu::quantity<si::current> (bu::quantity<si::time>) > i = iamp * bl::bind(static_cast<bu::dimensionless_quantity<si::system, double>::type (*)(const bu::quantity<si::plane_angle>&)>(bu::sin), 2.0 * pi * si::radian * f * bl::_1) + i0; cout << "Oscillating current:" << endl << "iamp = " << iamp << ", f = " << f << ", i0 = " << i0 << endl << "i(1.25e-3 * si::second) = " << i(1.25e-3 * si::second) << endl << endl; //////////////////////////////////////////////////////////////////////// // Geometric example: area calculation for a square //////////////////////////////////////////////////////////////////////// // Length constant const bu::quantity<si::length> l = 1.5 * si::meter; // Again an ugly static_cast is needed to bind pow<2> to the first // function argument. boost::function<bu::quantity<si::area> (bu::quantity<si::length>) > A = bl::bind(static_cast<bu::quantity<si::area> (*)(const bu::quantity<si::length>&)>(bu::pow<2>), bl::_1); cout << "Area of a square:" << endl << "A(" << l <<") = " << A(l) << endl << endl; //////////////////////////////////////////////////////////////////////// // Thermal example: temperature difference of two absolute temperatures //////////////////////////////////////////////////////////////////////// // Absolute temperature constants const bu::quantity<bu::absolute<si::temperature> > Tref = 273.15 * bu::absolute<si::temperature>(); const bu::quantity<bu::absolute<si::temperature> > Tamb = 300.00 * bu::absolute<si::temperature>(); boost::function<bu::quantity<si::temperature> (bu::quantity<bu::absolute<si::temperature> >, bu::quantity<bu::absolute<si::temperature> >)> dT = bl::_2 - bl::_1; cout << "Temperature difference of two absolute temperatures:" << endl << "dT(" << Tref << ", " << Tamb << ") = " << dT(Tref, Tamb) << endl << endl; return 0; } //]