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- // 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;
- }
- //]
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