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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="boost_units.Quick_Start"></a><a class="link" href="Quick_Start.html" title="Quick Start">Quick Start</a> |
| </h2></div></div></div> |
| <p> |
| Before discussing the basics of the library, we first define a few terms that |
| will be used frequently in the following : |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| <span class="bold"><strong>Base dimension</strong></span> : A base dimension is loosely |
| defined as a measurable entity of interest; in conventional dimensional |
| analysis, base dimensions include length ([L]), mass ([M]), time ([T]), |
| etc... but there is no specific restriction on what base dimensions can |
| be used. Base dimensions are essentially a tag type and provide no dimensional |
| analysis functionality themselves. |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong>Dimension</strong></span> : A collection of zero or more |
| base dimensions, each potentially raised to a different rational power. |
| For example, length = [L]^1, area = [L]^2, velocity = [L]^1/[T]^1, and |
| energy = [M]^1 [L]^2/[T]^2 are all dimensions. |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong>Base unit</strong></span> : A base unit represents a specific |
| measure of a dimension. For example, while length is an abstract measure |
| of distance, the meter is a concrete base unit of distance. Conversions |
| are defined using base units. Much like base dimensions, base units are |
| a tag type used solely to define units and do not support dimensional analysis |
| algebra. |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong>Unit</strong></span> : A set of base units raised to rational |
| exponents, e.g. m^1, kg^1, m^1/s^2. |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong>System</strong></span> : A unit system is a collection |
| of base units representing all the measurable entities of interest for |
| a specific problem. For example, the SI unit system defines seven base |
| units : length ([L]) in meters, mass ([M]) in kilograms, time ([T]) in |
| seconds, current ([I]) in amperes, temperature ([theta]) in kelvin, amount |
| ([N]) in moles, and luminous intensity ([J]) in candelas. All measurable |
| entities within the SI system can be represented as products of various |
| integer or rational powers of these seven base units. |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong>Quantity</strong></span> : A quantity represents a concrete |
| amount of a unit. Thus, while the meter is the base unit of length in the |
| SI system, 5.5 meters is a quantity of length in that system. |
| </li> |
| </ul></div> |
| <p> |
| To begin, we present two short tutorials. <a href="../../../libs/units/tutorial/tutorial_1.cpp" target="_top">Tutorial1</a> |
| demonstrates the use of <a href="http://en.wikipedia.org/wiki/SI_units" target="_top">SI</a> |
| units. After including the appropriate system headers and the headers for the |
| various SI units we will need (all SI units can be included with <code class="computeroutput"><a class="link" href="Reference.html#header.boost.units.systems.si_hpp" title="Header <boost/units/systems/si.hpp>">boost/units/systems/si.hpp</a></code>) and |
| for quantity I/O (<code class="computeroutput"><a class="link" href="Reference.html#header.boost.units.io_hpp" title="Header <boost/units/io.hpp>">boost/units/io.hpp</a></code>), |
| we define a function that computes the work, in joules, done by exerting a |
| force in newtons over a specified distance in meters and outputs the result |
| to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span></code>. The <span class="underline"><code class="computeroutput"><a class="link" href="../boost/units/quantity.html" title="Class template quantity">quantity</a></code></span> class accepts |
| a second template parameter as its value type; this parameter defaults to |
| <code class="computeroutput"><span class="keyword">double</span></code> if not otherwise specified. |
| To demonstrate the ease of using user-defined types in dimensional calculations, |
| we also present code for computing the complex impedance using <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span></code> |
| as the value type : |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">complex</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> |
| |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">typeof</span><span class="special">/</span><span class="identifier">std</span><span class="special">/</span><span class="identifier">complex</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">energy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">force</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">length</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">electric_potential</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">current</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">resistance</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">io</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">units</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">units</span><span class="special">::</span><span class="identifier">si</span><span class="special">;</span> |
| |
| <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">energy</span><span class="special">></span> |
| <span class="identifier">work</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">force</span><span class="special">>&</span> <span class="identifier">F</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">length</span><span class="special">>&</span> <span class="identifier">dx</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">F</span> <span class="special">*</span> <span class="identifier">dx</span><span class="special">;</span> <span class="comment">// Defines the relation: work = force * distance. |
| </span><span class="special">}</span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="comment">/// Test calculation of work. |
| </span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">force</span><span class="special">></span> <span class="identifier">F</span><span class="special">(</span><span class="number">2.0</span> <span class="special">*</span> <span class="identifier">newton</span><span class="special">);</span> <span class="comment">// Define a quantity of force. |
| </span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">length</span><span class="special">></span> <span class="identifier">dx</span><span class="special">(</span><span class="number">2.0</span> <span class="special">*</span> <span class="identifier">meter</span><span class="special">);</span> <span class="comment">// and a distance, |
| </span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">energy</span><span class="special">></span> <span class="identifier">E</span><span class="special">(</span><span class="identifier">work</span><span class="special">(</span><span class="identifier">F</span><span class="special">,</span><span class="identifier">dx</span><span class="special">));</span> <span class="comment">// and calculate the work done. |
| </span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"F = "</span> <span class="special"><<</span> <span class="identifier">F</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> |
| <span class="special"><<</span> <span class="string">"dx = "</span> <span class="special"><<</span> <span class="identifier">dx</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> |
| <span class="special"><<</span> <span class="string">"E = "</span> <span class="special"><<</span> <span class="identifier">E</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> |
| <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| |
| <span class="comment">/// Test and check complex quantities. |
| </span> <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">complex_type</span><span class="special">;</span> <span class="comment">// double real and imaginary parts. |
| </span> |
| <span class="comment">// Define some complex electrical quantities. |
| </span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">electric_potential</span><span class="special">,</span> <span class="identifier">complex_type</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">complex_type</span><span class="special">(</span><span class="number">12.5</span><span class="special">,</span> <span class="number">0.0</span><span class="special">)</span> <span class="special">*</span> <span class="identifier">volts</span><span class="special">;</span> |
| <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">current</span><span class="special">,</span> <span class="identifier">complex_type</span><span class="special">></span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">complex_type</span><span class="special">(</span><span class="number">3.0</span><span class="special">,</span> <span class="number">4.0</span><span class="special">)</span> <span class="special">*</span> <span class="identifier">amperes</span><span class="special">;</span> |
| <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">resistance</span><span class="special">,</span> <span class="identifier">complex_type</span><span class="special">></span> <span class="identifier">z</span> <span class="special">=</span> <span class="identifier">complex_type</span><span class="special">(</span><span class="number">1.5</span><span class="special">,</span> <span class="special">-</span><span class="number">2.0</span><span class="special">)</span> <span class="special">*</span> <span class="identifier">ohms</span><span class="special">;</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"V = "</span> <span class="special"><<</span> <span class="identifier">v</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> |
| <span class="special"><<</span> <span class="string">"I = "</span> <span class="special"><<</span> <span class="identifier">i</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> |
| <span class="special"><<</span> <span class="string">"Z = "</span> <span class="special"><<</span> <span class="identifier">z</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> |
| <span class="comment">// Calculate from Ohm's law voltage = current * resistance. |
| </span> <span class="special"><<</span> <span class="string">"I * Z = "</span> <span class="special"><<</span> <span class="identifier">i</span> <span class="special">*</span> <span class="identifier">z</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> |
| <span class="comment">// Check defined V is equal to calculated. |
| </span> <span class="special"><<</span> <span class="string">"I * Z == V? "</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">boolalpha</span> <span class="special"><<</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">*</span> <span class="identifier">z</span> <span class="special">==</span> <span class="identifier">v</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> |
| <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| The intent and function of the above code should be obvious; the output produced |
| is : |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">F</span> <span class="special">=</span> <span class="number">2</span> <span class="identifier">N</span> |
| <span class="identifier">dx</span> <span class="special">=</span> <span class="number">2</span> <span class="identifier">m</span> |
| <span class="identifier">E</span> <span class="special">=</span> <span class="number">4</span> <span class="identifier">J</span> |
| |
| <span class="identifier">V</span> <span class="special">=</span> <span class="special">(</span><span class="number">12.5</span><span class="special">,</span><span class="number">0</span><span class="special">)</span> <span class="identifier">V</span> |
| <span class="identifier">I</span> <span class="special">=</span> <span class="special">(</span><span class="number">3</span><span class="special">,</span><span class="number">4</span><span class="special">)</span> <span class="identifier">A</span> |
| <span class="identifier">Z</span> <span class="special">=</span> <span class="special">(</span><span class="number">1.5</span><span class="special">,-</span><span class="number">2</span><span class="special">)</span> <span class="identifier">Ohm</span> |
| <span class="identifier">I</span><span class="special">*</span><span class="identifier">Z</span> <span class="special">=</span> <span class="special">(</span><span class="number">12.5</span><span class="special">,</span><span class="number">0</span><span class="special">)</span> <span class="identifier">V</span> |
| <span class="identifier">I</span><span class="special">*</span><span class="identifier">Z</span> <span class="special">==</span> <span class="identifier">V</span><span class="special">?</span> <span class="keyword">true</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| While this library attempts to make simple dimensional computations easy to |
| code, it is in no way tied to any particular unit system (SI or otherwise). |
| Instead, it provides a highly flexible compile-time system for dimensional |
| analysis, supporting arbitrary collections of base dimensions, rational powers |
| of units, and explicit quantity conversions. It accomplishes all of this via |
| template metaprogramming techniques. With modern optimizing compilers, this |
| results in zero runtime overhead for quantity computations relative to the |
| same code without unit checking. |
| </p> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2003 -2008 Matthias Christian Schabel, 2007-2010 Steven |
| Watanabe<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
| </tr></table> |
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