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<div class="section">
<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<br>Copyright © 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>
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