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<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations"></a><a class="link" href="state_types__algebras_and_operations.html" title="State types, algebras and operations">State
types, algebras and operations</a>
</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.construction_resizing">Construction/Resizing</a></span></dt>
<dt><span class="section"><a href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations">Algebras
and Operations</a></span></dt>
<dt><span class="section"><a href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.adapt_your_own_operations">Adapt
your own operations</a></span></dt>
</dl></div>
<p>
In odeint the stepper algorithms are implemented independently of the underlying
fundamental mathematical operations. This is realized by giving the user
full control over the state type and the mathematical operations for this
state type. Technically, this is done by introducing three concepts: StateType,
Algebra, Operations. Most of the steppers in odeint expect three class types
fulfilling these concepts as template parameters. Note that these concepts
are not fully independent of each other but rather a valid combination must
be provided in order to make the steppers work. In the following we will
give some examples on reasonable state_type-algebra-operations combinations.
For the most common state types, like <code class="computeroutput"><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span></code> or <code class="computeroutput"><span class="identifier">array</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">,</span><span class="identifier">N</span><span class="special">&gt;</span></code>
the default values range_algebra and default_operations are perfectly fine
and odeint can be used as is without worrying about algebra/operations at
all.
</p>
<div class="important"><table border="0" summary="Important">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../../../doc/src/images/important.png"></td>
<th align="left">Important</th>
</tr>
<tr><td align="left" valign="top"><p>
state_type, algebra and operations are not independent, a valid combination
must be provided to make odeint work properly
</p></td></tr>
</table></div>
<p>
Moreover, as odeint handles the memory required for intermediate temporary
objects itself, it also needs knowledge about how to create state_type objects
and maybe how to allocate memory (resizing). All in all, the following things
have to be taken care of when odeint is used with non-standard state types:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
construction/destruction
</li>
<li class="listitem">
resizing (if possible/required)
</li>
<li class="listitem">
algebraic operations
</li>
</ul></div>
<p>
Again, odeint already provides basic interfaces for most of the usual state
types. So if you use a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span></code>,
or a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span></code> as state type no additional work
is required, they just work out of the box.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.construction_resizing"></a><a class="link" href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.construction_resizing" title="Construction/Resizing">Construction/Resizing</a>
</h4></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.construction_resizing.using_the_container_interface">Using
the container interface</a></span></dt>
<dt><span class="section"><a href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.construction_resizing.std__list">std::list</a></span></dt>
</dl></div>
<p>
We distinguish between two basic state types: fixed sized and dynamically
sized. For fixed size state types the default constructor <code class="computeroutput"><span class="identifier">state_type</span><span class="special">()</span></code>
already allocates the required memory, prominent example is <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">N</span><span class="special">&gt;</span></code>. Dynamically sized types have to be
resized to make sure enough memory is allocated, the standard constructor
does not take care of the resizing. Examples for this are the STL containers
like <code class="computeroutput"><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span></code>.
</p>
<p>
The most easy way of getting your own state type to work with odeint is
to use a fixed size state, base calculations on the range_algebra and provide
the following functionality:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Expression
</p>
</th>
<th>
<p>
Type
</p>
</th>
<th>
<p>
Semantics
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
Construct State
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">State</span> <span class="identifier">x</span><span class="special">()</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">void</span></code>
</p>
</td>
<td>
<p>
Creates an instance of <code class="computeroutput"><span class="identifier">State</span></code>
and allocates memory.
</p>
</td>
</tr>
<tr>
<td>
<p>
Begin of the sequence
</p>
</td>
<td>
<p>
boost::begin(x)
</p>
</td>
<td>
<p>
Iterator
</p>
</td>
<td>
<p>
Returns an iterator pointing to the begin of the sequence
</p>
</td>
</tr>
<tr>
<td>
<p>
End of the sequence
</p>
</td>
<td>
<p>
boost::end(x)
</p>
</td>
<td>
<p>
Iterator
</p>
</td>
<td>
<p>
Returns an iterator pointing to the end of the sequence
</p>
</td>
</tr>
</tbody>
</table></div>
<div class="warning"><table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../../../doc/src/images/warning.png"></td>
<th align="left">Warning</th>
</tr>
<tr><td align="left" valign="top"><p>
If your state type does not allocate memory by default construction,
you <span class="bold"><strong>must define it as resizeable</strong></span> and
provide resize functionality (see below). Otherwise segmentation faults
will occur.
</p></td></tr>
</table></div>
<p>
So fixed sized arrays supported by <a href="http://www.boost.org/doc/libs/release/libs/range/" target="_top">Boost.Range</a>
immediately work with odeint. For dynamically sized arrays one has to additionally
supply the resize functionality. First, the state has to be tagged as resizeable
by specializing the struct <code class="computeroutput"><span class="identifier">is_resizeable</span></code>
which consists of one typedef and one bool value:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Expression
</p>
</th>
<th>
<p>
Type
</p>
</th>
<th>
<p>
Semantics
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
Resizability
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">is_resizeable</span><span class="special">&lt;</span><span class="identifier">State</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">true_type</span></code> or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">false_type</span></code>
</p>
</td>
<td>
<p>
Determines resizeability of the state type, returns <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">true_type</span></code> if the state is resizeable.
</p>
</td>
</tr>
<tr>
<td>
<p>
Resizability
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">is_resizeable</span><span class="special">&lt;</span><span class="identifier">State</span><span class="special">&gt;::</span><span class="identifier">value</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">bool</span></code>
</p>
</td>
<td>
<p>
Same as above, but with <code class="computeroutput"><span class="keyword">bool</span></code>
value.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
Defining <code class="computeroutput"><span class="identifier">type</span></code> to be <code class="computeroutput"><span class="identifier">true_type</span></code> and <code class="computeroutput"><span class="identifier">value</span></code>
as <code class="computeroutput"><span class="keyword">true</span></code> tells odeint that
your state is resizeable. By default, odeint now expects the support of
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">size</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code> and
a <code class="computeroutput"><span class="identifier">x</span><span class="special">.</span><span class="identifier">resize</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">size</span><span class="special">(</span><span class="identifier">y</span><span class="special">)</span> <span class="special">)</span></code>
member function for resizing:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Expression
</p>
</th>
<th>
<p>
Type
</p>
</th>
<th>
<p>
Semantics
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
Get size
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">size</span><span class="special">(</span>
<span class="identifier">x</span> <span class="special">)</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">size_type</span></code>
</p>
</td>
<td>
<p>
Returns the current size of x.
</p>
</td>
</tr>
<tr>
<td>
<p>
Resize
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">x</span><span class="special">.</span><span class="identifier">resize</span><span class="special">(</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">size</span><span class="special">(</span>
<span class="identifier">y</span> <span class="special">)</span>
<span class="special">)</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">void</span></code>
</p>
</td>
<td>
<p>
Resizes x to have the same size as y.
</p>
</td>
</tr>
</tbody>
</table></div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.construction_resizing.using_the_container_interface"></a><a class="link" href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.construction_resizing.using_the_container_interface" title="Using the container interface">Using
the container interface</a>
</h5></div></div></div>
<p>
As a first example we take the most simple case and implement our own
vector <code class="computeroutput"><span class="identifier">my_vector</span></code> which
will provide a container interface. This makes <a href="http://www.boost.org/doc/libs/release/libs/range/" target="_top">Boost.Range</a>
working out-of-box. We add a little functionality to our vector which
makes it allocate some default capacity by construction. This is helpful
when using resizing as then a resize can be assured to not require a
new allocation.
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">int</span> <span class="identifier">MAX_N</span> <span class="special">&gt;</span>
<span class="keyword">class</span> <span class="identifier">my_vector</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span> <span class="keyword">double</span> <span class="special">&gt;</span> <span class="identifier">vector</span><span class="special">;</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">iterator</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special">::</span><span class="identifier">const_iterator</span> <span class="identifier">const_iterator</span><span class="special">;</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="identifier">my_vector</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">size_t</span> <span class="identifier">N</span> <span class="special">)</span>
<span class="special">:</span> <span class="identifier">m_v</span><span class="special">(</span> <span class="identifier">N</span> <span class="special">)</span>
<span class="special">{</span>
<span class="identifier">m_v</span><span class="special">.</span><span class="identifier">reserve</span><span class="special">(</span> <span class="identifier">MAX_N</span> <span class="special">);</span>
<span class="special">}</span>
<span class="identifier">my_vector</span><span class="special">()</span>
<span class="special">:</span> <span class="identifier">m_v</span><span class="special">()</span>
<span class="special">{</span>
<span class="identifier">m_v</span><span class="special">.</span><span class="identifier">reserve</span><span class="special">(</span> <span class="identifier">MAX_N</span> <span class="special">);</span>
<span class="special">}</span>
<span class="comment">// ... [ implement container interface ]</span>
</pre>
<p>
</p>
<p>
The only thing that has to be done other than defining is thus declaring
my_vector as resizeable:
</p>
<p>
</p>
<pre class="programlisting"><span class="comment">// define my_vector as resizeable</span>
<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">numeric</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">odeint</span> <span class="special">{</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="identifier">size_t</span> <span class="identifier">N</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">is_resizeable</span><span class="special">&lt;</span> <span class="identifier">my_vector</span><span class="special">&lt;</span><span class="identifier">N</span><span class="special">&gt;</span> <span class="special">&gt;</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">true_type</span> <span class="identifier">type</span><span class="special">;</span>
<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">value</span> <span class="special">=</span> <span class="identifier">type</span><span class="special">::</span><span class="identifier">value</span><span class="special">;</span>
<span class="special">};</span>
<span class="special">}</span> <span class="special">}</span> <span class="special">}</span>
</pre>
<p>
</p>
<p>
If we wouldn't specialize the <code class="computeroutput"><span class="identifier">is_resizeable</span></code>
template, the code would still compile but odeint would not adjust the
size of temporary internal instances of my_vector and hence try to fill
zero-sized vectors resulting in segmentation faults! The full example
can be found in <a href="https://github.com/headmyshoulder/odeint-v2/blob/master/examples/my_vector.cpp" target="_top">my_vector.cpp</a>
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.construction_resizing.std__list"></a><a class="link" href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.construction_resizing.std__list" title="std::list">std::list</a>
</h5></div></div></div>
<p>
If your state type does work with <a href="http://www.boost.org/doc/libs/release/libs/range/" target="_top">Boost.Range</a>,
but handles resizing differently you are required to specialize two implementations
used by odeint to check a state's size and to resize:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Expression
</p>
</th>
<th>
<p>
Type
</p>
</th>
<th>
<p>
Semantics
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
Check size
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">same_size_impl</span><span class="special">&lt;</span><span class="identifier">State</span><span class="special">,</span><span class="identifier">State</span><span class="special">&gt;::</span><span class="identifier">same_size</span><span class="special">(</span><span class="identifier">x</span>
<span class="special">,</span> <span class="identifier">y</span><span class="special">)</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">bool</span></code>
</p>
</td>
<td>
<p>
Returns true if the size of x equals the size of y.
</p>
</td>
</tr>
<tr>
<td>
<p>
Resize
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">resize_impl</span><span class="special">&lt;</span><span class="identifier">State</span><span class="special">,</span><span class="identifier">State</span><span class="special">&gt;::</span><span class="identifier">resize</span><span class="special">(</span><span class="identifier">x</span>
<span class="special">,</span> <span class="identifier">y</span><span class="special">)</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">void</span></code>
</p>
</td>
<td>
<p>
Resizes x to have the same size as y.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
As an example we will use a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span></code>
as state type in odeint. Because <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span></code>
is not supported by <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">size</span></code>
we have to replace the same_size and resize implementation to get list
to work with odeint. The following code shows the required template specializations:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span><span class="special">&lt;</span> <span class="keyword">double</span> <span class="special">&gt;</span> <span class="identifier">state_type</span><span class="special">;</span>
<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">numeric</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">odeint</span> <span class="special">{</span>
<span class="keyword">template</span><span class="special">&lt;</span> <span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">is_resizeable</span><span class="special">&lt;</span> <span class="identifier">state_type</span> <span class="special">&gt;</span>
<span class="special">{</span> <span class="comment">// declare resizeability</span>
<span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">true_type</span> <span class="identifier">type</span><span class="special">;</span>
<span class="keyword">const</span> <span class="keyword">static</span> <span class="keyword">bool</span> <span class="identifier">value</span> <span class="special">=</span> <span class="identifier">type</span><span class="special">::</span><span class="identifier">value</span><span class="special">;</span>
<span class="special">};</span>
<span class="keyword">template</span><span class="special">&lt;</span> <span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">same_size_impl</span><span class="special">&lt;</span> <span class="identifier">state_type</span> <span class="special">,</span> <span class="identifier">state_type</span> <span class="special">&gt;</span>
<span class="special">{</span> <span class="comment">// define how to check size</span>
<span class="keyword">static</span> <span class="keyword">bool</span> <span class="identifier">same_size</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">state_type</span> <span class="special">&amp;</span><span class="identifier">v1</span> <span class="special">,</span>
<span class="keyword">const</span> <span class="identifier">state_type</span> <span class="special">&amp;</span><span class="identifier">v2</span> <span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">v1</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">v2</span><span class="special">.</span><span class="identifier">size</span><span class="special">();</span>
<span class="special">}</span>
<span class="special">};</span>
<span class="keyword">template</span><span class="special">&lt;</span> <span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">resize_impl</span><span class="special">&lt;</span> <span class="identifier">state_type</span> <span class="special">,</span> <span class="identifier">state_type</span> <span class="special">&gt;</span>
<span class="special">{</span> <span class="comment">// define how to resize</span>
<span class="keyword">static</span> <span class="keyword">void</span> <span class="identifier">resize</span><span class="special">(</span> <span class="identifier">state_type</span> <span class="special">&amp;</span><span class="identifier">v1</span> <span class="special">,</span>
<span class="keyword">const</span> <span class="identifier">state_type</span> <span class="special">&amp;</span><span class="identifier">v2</span> <span class="special">)</span>
<span class="special">{</span>
<span class="identifier">v1</span><span class="special">.</span><span class="identifier">resize</span><span class="special">(</span> <span class="identifier">v2</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">);</span>
<span class="special">}</span>
<span class="special">};</span>
<span class="special">}</span> <span class="special">}</span> <span class="special">}</span>
</pre>
<p>
</p>
<p>
With these definitions odeint knows how to resize <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span></code>s
and so they can be used as state types. A complete example can be found
in <a href="https://github.com/headmyshoulder/odeint-v2/blob/master/examples/list_lattice.cpp" target="_top">list_lattice.cpp</a>.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations"></a><a class="link" href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations" title="Algebras and Operations">Algebras
and Operations</a>
</h4></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations.gsl_vector">GSL
Vector</a></span></dt>
<dt><span class="section"><a href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations.vector_space_algebra">Vector
Space Algebra</a></span></dt>
<dt><span class="section"><a href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations.point_type">Point
type</a></span></dt>
</dl></div>
<p>
To provide maximum flexibility odeint is implemented in a highly modularized
way. This means it is possible to change the underlying mathematical operations
without touching the integration algorithms. The fundamental mathematical
operations are those of a vector space, that is addition of <code class="computeroutput"><span class="identifier">state_types</span></code> and multiplication of <code class="computeroutput"><span class="identifier">state_type</span></code>s with a scalar (<code class="computeroutput"><span class="identifier">time_type</span></code>). In odeint this is realized
in two concepts: <span class="underline">Algebra</span> and <span class="underline">Operations</span>. The standard way how this works
is by the range algebra which provides functions that apply a specific
operation to each of the individual elements of a container based on the
<a href="http://www.boost.org/doc/libs/release/libs/range/" target="_top">Boost.Range</a>
library. If your state type is not supported by <a href="http://www.boost.org/doc/libs/release/libs/range/" target="_top">Boost.Range</a>
there are several possibilities to tell odeint how to do algebraic operations:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Implement <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">begin</span></code> and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">end</span></code>
for your state type so it works with <a href="http://www.boost.org/doc/libs/release/libs/range/" target="_top">Boost.Range</a>.
</li>
<li class="listitem">
Implement vector-vector addition operator <code class="computeroutput"><span class="special">+</span></code>
and scalar-vector multiplication operator <code class="computeroutput"><span class="special">*</span></code>
and use the non-standard <code class="computeroutput"><span class="identifier">vector_space_algebra</span></code>.
</li>
<li class="listitem">
Implement your own algebra that implements the required functions.
</li>
</ul></div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations.gsl_vector"></a><a class="link" href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations.gsl_vector" title="GSL Vector">GSL
Vector</a>
</h5></div></div></div>
<p>
In the following example we will try to use the <code class="computeroutput"><span class="identifier">gsl_vector</span></code>
type from <a href="http://www.gsl.org" target="_top">GSL</a> (GNU Scientific
Library) as state type in odeint. We will realize this by implementing
a wrapper around the gsl_vector that takes care of construction/destruction.
Also, <a href="http://www.boost.org/doc/libs/release/libs/range/" target="_top">Boost.Range</a>
is extended such that it works with <code class="computeroutput"><span class="identifier">gsl_vector</span></code>s
as well which required also the implementation of a new <code class="computeroutput"><span class="identifier">gsl_iterator</span></code>.
</p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
odeint already includes all the code presented here, see <a href="https://github.com/headmyshoulder/odeint-v2/blob/master/boost/numeric/odeint/external/gsl/gsl_wrapper.hpp" target="_top">gsl_wrapper.hpp</a>,
so <code class="computeroutput"><span class="identifier">gsl_vector</span></code>s can
be used straight out-of-box. The following description is just for
educational purpose.
</p></td></tr>
</table></div>
<p>
The GSL is a C library, so <code class="computeroutput"><span class="identifier">gsl_vector</span></code>
has neither constructor, nor destructor or any <code class="computeroutput"><span class="identifier">begin</span></code>
or <code class="computeroutput"><span class="identifier">end</span></code> function, no iterators
at all. So to make it work with odeint plenty of things have to be implemented.
Note that all of the work shown here is already included in odeint, so
using <code class="computeroutput"><span class="identifier">gsl_vector</span></code>s in
odeint doesn't require any further adjustments. We present it here just
as an educational example. We start with defining appropriate constructors
and destructors. This is done by specializing the <code class="computeroutput"><span class="identifier">state_wrapper</span></code>
for <code class="computeroutput"><span class="identifier">gsl_vector</span></code>. State
wrappers are used by the steppers internally to create and manage temporary
instances of state types:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;&gt;</span>
<span class="keyword">struct</span> <span class="identifier">state_wrapper</span><span class="special">&lt;</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="special">&gt;</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="keyword">double</span> <span class="identifier">value_type</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="identifier">state_type</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">state_wrapper</span><span class="special">&lt;</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="special">&gt;</span> <span class="identifier">state_wrapper_type</span><span class="special">;</span>
<span class="identifier">state_type</span> <span class="identifier">m_v</span><span class="special">;</span>
<span class="identifier">state_wrapper</span><span class="special">(</span> <span class="special">)</span>
<span class="special">{</span>
<span class="identifier">m_v</span> <span class="special">=</span> <span class="identifier">gsl_vector_alloc</span><span class="special">(</span> <span class="number">1</span> <span class="special">);</span>
<span class="special">}</span>
<span class="identifier">state_wrapper</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">state_wrapper_type</span> <span class="special">&amp;</span><span class="identifier">x</span> <span class="special">)</span>
<span class="special">{</span>
<span class="identifier">resize</span><span class="special">(</span> <span class="identifier">m_v</span> <span class="special">,</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">m_v</span> <span class="special">);</span>
<span class="identifier">gsl_vector_memcpy</span><span class="special">(</span> <span class="identifier">m_v</span> <span class="special">,</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">m_v</span> <span class="special">);</span>
<span class="special">}</span>
<span class="special">~</span><span class="identifier">state_wrapper</span><span class="special">()</span>
<span class="special">{</span>
<span class="identifier">gsl_vector_free</span><span class="special">(</span> <span class="identifier">m_v</span> <span class="special">);</span>
<span class="special">}</span>
<span class="special">};</span>
</pre>
<p>
</p>
<p>
This <code class="computeroutput"><span class="identifier">state_wrapper</span></code> specialization
tells odeint how gsl_vectors are created, copied and destroyed. Next
we need resizing, this is required because gsl_vectors are dynamically
sized objects:
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;&gt;</span>
<span class="keyword">struct</span> <span class="identifier">is_resizeable</span><span class="special">&lt;</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="special">&gt;</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">true_type</span> <span class="identifier">type</span><span class="special">;</span>
<span class="keyword">const</span> <span class="keyword">static</span> <span class="keyword">bool</span> <span class="identifier">value</span> <span class="special">=</span> <span class="identifier">type</span><span class="special">::</span><span class="identifier">value</span><span class="special">;</span>
<span class="special">};</span>
<span class="keyword">template</span> <span class="special">&lt;&gt;</span>
<span class="keyword">struct</span> <span class="identifier">same_size_impl</span><span class="special">&lt;</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="special">,</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="special">&gt;</span>
<span class="special">{</span>
<span class="keyword">static</span> <span class="keyword">bool</span> <span class="identifier">same_size</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="identifier">x</span> <span class="special">,</span> <span class="keyword">const</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="identifier">y</span> <span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">x</span><span class="special">-&gt;</span><span class="identifier">size</span> <span class="special">==</span> <span class="identifier">y</span><span class="special">-&gt;</span><span class="identifier">size</span><span class="special">;</span>
<span class="special">}</span>
<span class="special">};</span>
<span class="keyword">template</span> <span class="special">&lt;&gt;</span>
<span class="keyword">struct</span> <span class="identifier">resize_impl</span><span class="special">&lt;</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="special">,</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="special">&gt;</span>
<span class="special">{</span>
<span class="keyword">static</span> <span class="keyword">void</span> <span class="identifier">resize</span><span class="special">(</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="identifier">x</span> <span class="special">,</span> <span class="keyword">const</span> <span class="identifier">gsl_vector</span><span class="special">*</span> <span class="identifier">y</span> <span class="special">)</span>
<span class="special">{</span>
<span class="identifier">gsl_vector_free</span><span class="special">(</span> <span class="identifier">x</span> <span class="special">);</span>
<span class="identifier">x</span> <span class="special">=</span> <span class="identifier">gsl_vector_alloc</span><span class="special">(</span> <span class="identifier">y</span><span class="special">-&gt;</span><span class="identifier">size</span> <span class="special">);</span>
<span class="special">}</span>
<span class="special">};</span>
</pre>
<p>
</p>
<p>
Up to now, we defined creation/destruction and resizing, but gsl_vectors
also don't support iterators, so we first implement a gsl iterator:
</p>
<p>
</p>
<pre class="programlisting"><span class="comment">/*
* defines an iterator for gsl_vector
*/</span>
<span class="keyword">class</span> <span class="identifier">gsl_vector_iterator</span>
<span class="special">:</span> <span class="keyword">public</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">iterator_facade</span><span class="special">&lt;</span> <span class="identifier">gsl_vector_iterator</span> <span class="special">,</span> <span class="keyword">double</span> <span class="special">,</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">random_access_traversal_tag</span> <span class="special">&gt;</span>
<span class="special">{</span>
<span class="keyword">public</span> <span class="special">:</span>
<span class="identifier">gsl_vector_iterator</span><span class="special">(</span> <span class="keyword">void</span> <span class="special">):</span> <span class="identifier">m_p</span><span class="special">(</span><span class="number">0</span><span class="special">)</span> <span class="special">,</span> <span class="identifier">m_stride</span><span class="special">(</span> <span class="number">0</span> <span class="special">)</span> <span class="special">{</span> <span class="special">}</span>
<span class="keyword">explicit</span> <span class="identifier">gsl_vector_iterator</span><span class="special">(</span> <span class="identifier">gsl_vector</span> <span class="special">*</span><span class="identifier">p</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">m_p</span><span class="special">(</span> <span class="identifier">p</span><span class="special">-&gt;</span><span class="identifier">data</span> <span class="special">)</span> <span class="special">,</span> <span class="identifier">m_stride</span><span class="special">(</span> <span class="identifier">p</span><span class="special">-&gt;</span><span class="identifier">stride</span> <span class="special">)</span> <span class="special">{</span> <span class="special">}</span>
<span class="keyword">friend</span> <span class="identifier">gsl_vector_iterator</span> <span class="identifier">end_iterator</span><span class="special">(</span> <span class="identifier">gsl_vector</span> <span class="special">*</span> <span class="special">);</span>
<span class="keyword">private</span> <span class="special">:</span>
<span class="keyword">friend</span> <span class="keyword">class</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">iterator_core_access</span><span class="special">;</span>
<span class="keyword">friend</span> <span class="keyword">class</span> <span class="identifier">const_gsl_vector_iterator</span><span class="special">;</span>
<span class="keyword">void</span> <span class="identifier">increment</span><span class="special">(</span> <span class="keyword">void</span> <span class="special">)</span> <span class="special">{</span> <span class="identifier">m_p</span> <span class="special">+=</span> <span class="identifier">m_stride</span><span class="special">;</span> <span class="special">}</span>
<span class="keyword">void</span> <span class="identifier">decrement</span><span class="special">(</span> <span class="keyword">void</span> <span class="special">)</span> <span class="special">{</span> <span class="identifier">m_p</span> <span class="special">-=</span> <span class="identifier">m_stride</span><span class="special">;</span> <span class="special">}</span>
<span class="keyword">void</span> <span class="identifier">advance</span><span class="special">(</span> <span class="identifier">ptrdiff_t</span> <span class="identifier">n</span> <span class="special">)</span> <span class="special">{</span> <span class="identifier">m_p</span> <span class="special">+=</span> <span class="identifier">n</span><span class="special">*</span><span class="identifier">m_stride</span><span class="special">;</span> <span class="special">}</span>
<span class="keyword">bool</span> <span class="identifier">equal</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">gsl_vector_iterator</span> <span class="special">&amp;</span><span class="identifier">other</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="keyword">this</span><span class="special">-&gt;</span><span class="identifier">m_p</span> <span class="special">==</span> <span class="identifier">other</span><span class="special">.</span><span class="identifier">m_p</span><span class="special">;</span> <span class="special">}</span>
<span class="keyword">bool</span> <span class="identifier">equal</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">const_gsl_vector_iterator</span> <span class="special">&amp;</span><span class="identifier">other</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="keyword">double</span><span class="special">&amp;</span> <span class="identifier">dereference</span><span class="special">(</span> <span class="keyword">void</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="special">*</span><span class="identifier">m_p</span><span class="special">;</span> <span class="special">}</span>
<span class="keyword">double</span> <span class="special">*</span><span class="identifier">m_p</span><span class="special">;</span>
<span class="identifier">size_t</span> <span class="identifier">m_stride</span><span class="special">;</span>
<span class="special">};</span>
</pre>
<p>
A similar class exists for the <code class="computeroutput"><span class="keyword">const</span></code>
version of the iterator. Then we have a function returning the end iterator
(similarly for <code class="computeroutput"><span class="keyword">const</span></code> again):
</p>
<pre class="programlisting"><span class="identifier">gsl_vector_iterator</span> <span class="identifier">end_iterator</span><span class="special">(</span> <span class="identifier">gsl_vector</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">)</span>
<span class="special">{</span>
<span class="identifier">gsl_vector_iterator</span> <span class="identifier">iter</span><span class="special">(</span> <span class="identifier">x</span> <span class="special">);</span>
<span class="identifier">iter</span><span class="special">.</span><span class="identifier">m_p</span> <span class="special">+=</span> <span class="identifier">iter</span><span class="special">.</span><span class="identifier">m_stride</span> <span class="special">*</span> <span class="identifier">x</span><span class="special">-&gt;</span><span class="identifier">size</span><span class="special">;</span>
<span class="keyword">return</span> <span class="identifier">iter</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
Finally, the bindings for <a href="http://www.boost.org/doc/libs/release/libs/range/" target="_top">Boost.Range</a>
are added:
</p>
<pre class="programlisting"><span class="comment">// template&lt;&gt;</span>
<span class="keyword">inline</span> <span class="identifier">gsl_vector_iterator</span> <span class="identifier">range_begin</span><span class="special">(</span> <span class="identifier">gsl_vector</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">gsl_vector_iterator</span><span class="special">(</span> <span class="identifier">x</span> <span class="special">);</span>
<span class="special">}</span>
<span class="comment">// template&lt;&gt;</span>
<span class="keyword">inline</span> <span class="identifier">gsl_vector_iterator</span> <span class="identifier">range_end</span><span class="special">(</span> <span class="identifier">gsl_vector</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">end_iterator</span><span class="special">(</span> <span class="identifier">x</span> <span class="special">);</span>
<span class="special">}</span>
</pre>
<p>
Again with similar definitions for the <code class="computeroutput"><span class="keyword">const</span></code>
versions. This eventually makes odeint work with gsl vectors as state
types. The full code for these bindings is found in <a href="https://github.com/headmyshoulder/odeint-v2/blob/master/boost/numeric/odeint/external/gsl/gsl_wrapper.hpp" target="_top">gsl_wrapper.hpp</a>.
It might look rather complicated but keep in mind that gsl is a pre-compiled
C library.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations.vector_space_algebra"></a><a class="link" href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations.vector_space_algebra" title="Vector Space Algebra">Vector
Space Algebra</a>
</h5></div></div></div>
<p>
As seen above, the standard way of performing algebraic operations on
container-like state types in odeint is to iterate through the elements
of the container and perform the operations element-wise on the underlying
value type. This is realized by means of the <code class="computeroutput"><span class="identifier">range_algebra</span></code>
that uses <a href="http://www.boost.org/doc/libs/release/libs/range/" target="_top">Boost.Range</a>
for obtaining iterators of the state types. However, there are other
ways to implement the algebraic operations on containers, one of which
is defining the addition/multiplication operators for the containers
directly and then using the <code class="computeroutput"><span class="identifier">vector_space_algebra</span></code>.
If you use this algebra, the following operators have to be defined for
the state_type:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Expression
</p>
</th>
<th>
<p>
Type
</p>
</th>
<th>
<p>
Semantics
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
Addition
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">x</span> <span class="special">+</span>
<span class="identifier">y</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">state_type</span></code>
</p>
</td>
<td>
<p>
Calculates the vector sum 'x+y'.
</p>
</td>
</tr>
<tr>
<td>
<p>
Assign addition
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">x</span> <span class="special">+=</span>
<span class="identifier">y</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">state_type</span></code>
</p>
</td>
<td>
<p>
Performs x+y in place.
</p>
</td>
</tr>
<tr>
<td>
<p>
Scalar multiplication
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">a</span> <span class="special">*</span>
<span class="identifier">x</span> </code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">state_type</span></code>
</p>
</td>
<td>
<p>
Performs multiplication of vector x with scalar a.
</p>
</td>
</tr>
<tr>
<td>
<p>
Assign scalar multiplication
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">x</span> <span class="special">*=</span>
<span class="identifier">a</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">state_type</span></code>
</p>
</td>
<td>
<p>
Performs in-place multiplication of vector x with scalar a.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
Defining these operators makes your state type work with any basic Runge-Kutta
stepper. However, if you want to use step-size control, some more functionality
is required. Specifically, operations like <span class="emphasis"><em>max<sub>i</sub>( |err<sub>i</sub>| / (alpha
* |s<sub>i</sub>|) )</em></span> have to be performed. <span class="emphasis"><em>err</em></span> and
<span class="emphasis"><em>s</em></span> are state_types, alpha is a scalar. As you can
see, we need element wise absolute value and division as well as an reduce
operation to get the maximum value. So for controlled steppers the following
things have to be implemented:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Expression
</p>
</th>
<th>
<p>
Type
</p>
</th>
<th>
<p>
Semantics
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
Division
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">x</span> <span class="special">/</span>
<span class="identifier">y</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">state_type</span></code>
</p>
</td>
<td>
<p>
Calculates the element-wise division 'x/y'
</p>
</td>
</tr>
<tr>
<td>
<p>
Absolute value
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">abs</span><span class="special">(</span>
<span class="identifier">x</span> <span class="special">)</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">state_type</span></code>
</p>
</td>
<td>
<p>
Element wise absolute value
</p>
</td>
</tr>
<tr>
<td>
<p>
Reduce
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">vector_space_reduce_impl</span><span class="special">&lt;</span> <span class="identifier">state_type</span>
<span class="special">&gt;::</span><span class="identifier">reduce</span><span class="special">(</span> <span class="identifier">state</span>
<span class="special">,</span> <span class="identifier">operation</span>
<span class="special">,</span> <span class="identifier">init</span>
<span class="special">)</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">value_type</span></code>
</p>
</td>
<td>
<p>
Performs the <code class="computeroutput"><span class="identifier">operation</span></code>
for subsequently each element of <code class="computeroutput"><span class="identifier">state</span></code>
and returns the aggregate value. E.g.
</p>
<p>
<code class="computeroutput"><span class="identifier">init</span> <span class="special">=</span>
<span class="keyword">operator</span><span class="special">(</span>
<span class="identifier">init</span> <span class="special">,</span>
<span class="identifier">state</span><span class="special">[</span><span class="number">0</span><span class="special">]</span>
<span class="special">);</span></code>
</p>
<p>
<code class="computeroutput"><span class="identifier">init</span> <span class="special">=</span>
<span class="keyword">operator</span><span class="special">(</span>
<span class="identifier">init</span> <span class="special">,</span>
<span class="identifier">state</span><span class="special">[</span><span class="number">1</span><span class="special">]</span>
<span class="special">)</span></code>
</p>
<p>
<code class="computeroutput"><span class="special">...</span></code>
</p>
</td>
</tr>
</tbody>
</table></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations.point_type"></a><a class="link" href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations.point_type" title="Point type">Point
type</a>
</h5></div></div></div>
<p>
Here we show how to implement the required operators on a state type.
As example we define a new class <code class="computeroutput"><span class="identifier">point3D</span></code>
representing a three-dimensional vector with components x,y,z and define
addition and scalar multiplication operators for it. We use <a href="http://www.boost.org/doc/libs/release/libs/utility/operators.htm" target="_top">Boost.Operators</a>
to reduce the amount of code to be written. The class for the point type
looks as follows:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">point3D</span> <span class="special">:</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">additive1</span><span class="special">&lt;</span> <span class="identifier">point3D</span> <span class="special">,</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">additive2</span><span class="special">&lt;</span> <span class="identifier">point3D</span> <span class="special">,</span> <span class="keyword">double</span> <span class="special">,</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiplicative2</span><span class="special">&lt;</span> <span class="identifier">point3D</span> <span class="special">,</span> <span class="keyword">double</span> <span class="special">&gt;</span> <span class="special">&gt;</span> <span class="special">&gt;</span>
<span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="keyword">double</span> <span class="identifier">x</span> <span class="special">,</span> <span class="identifier">y</span> <span class="special">,</span> <span class="identifier">z</span><span class="special">;</span>
<span class="identifier">point3D</span><span class="special">()</span>
<span class="special">:</span> <span class="identifier">x</span><span class="special">(</span> <span class="number">0.0</span> <span class="special">)</span> <span class="special">,</span> <span class="identifier">y</span><span class="special">(</span> <span class="number">0.0</span> <span class="special">)</span> <span class="special">,</span> <span class="identifier">z</span><span class="special">(</span> <span class="number">0.0</span> <span class="special">)</span>
<span class="special">{</span> <span class="special">}</span>
<span class="identifier">point3D</span><span class="special">(</span> <span class="keyword">const</span> <span class="keyword">double</span> <span class="identifier">val</span> <span class="special">)</span>
<span class="special">:</span> <span class="identifier">x</span><span class="special">(</span> <span class="identifier">val</span> <span class="special">)</span> <span class="special">,</span> <span class="identifier">y</span><span class="special">(</span> <span class="identifier">val</span> <span class="special">)</span> <span class="special">,</span> <span class="identifier">z</span><span class="special">(</span> <span class="identifier">val</span> <span class="special">)</span>
<span class="special">{</span> <span class="special">}</span>
<span class="identifier">point3D</span><span class="special">(</span> <span class="keyword">const</span> <span class="keyword">double</span> <span class="identifier">_x</span> <span class="special">,</span> <span class="keyword">const</span> <span class="keyword">double</span> <span class="identifier">_y</span> <span class="special">,</span> <span class="keyword">const</span> <span class="keyword">double</span> <span class="identifier">_z</span> <span class="special">)</span>
<span class="special">:</span> <span class="identifier">x</span><span class="special">(</span> <span class="identifier">_x</span> <span class="special">)</span> <span class="special">,</span> <span class="identifier">y</span><span class="special">(</span> <span class="identifier">_y</span> <span class="special">)</span> <span class="special">,</span> <span class="identifier">z</span><span class="special">(</span> <span class="identifier">_z</span> <span class="special">)</span>
<span class="special">{</span> <span class="special">}</span>
<span class="identifier">point3D</span><span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">+=(</span> <span class="keyword">const</span> <span class="identifier">point3D</span> <span class="special">&amp;</span><span class="identifier">p</span> <span class="special">)</span>
<span class="special">{</span>
<span class="identifier">x</span> <span class="special">+=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">x</span><span class="special">;</span> <span class="identifier">y</span> <span class="special">+=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">y</span><span class="special">;</span> <span class="identifier">z</span> <span class="special">+=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">z</span><span class="special">;</span>
<span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;</span>
<span class="special">}</span>
<span class="identifier">point3D</span><span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">*=(</span> <span class="keyword">const</span> <span class="keyword">double</span> <span class="identifier">a</span> <span class="special">)</span>
<span class="special">{</span>
<span class="identifier">x</span> <span class="special">*=</span> <span class="identifier">a</span><span class="special">;</span> <span class="identifier">y</span> <span class="special">*=</span> <span class="identifier">a</span><span class="special">;</span> <span class="identifier">z</span> <span class="special">*=</span> <span class="identifier">a</span><span class="special">;</span>
<span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;</span>
<span class="special">}</span>
<span class="special">};</span>
</pre>
<p>
</p>
<p>
By deriving from <a href="http://www.boost.org/doc/libs/release/libs/utility/operators.htm" target="_top">Boost.Operators</a>
classes we don't have to define outer class operators like <code class="computeroutput"><span class="keyword">operator</span><span class="special">+(</span> <span class="identifier">point3D</span> <span class="special">,</span>
<span class="identifier">point3D</span> <span class="special">)</span></code>
because that is taken care of by the operators library. Note that for
simple Runge-Kutta schemes (like <code class="computeroutput"><span class="identifier">runge_kutta4</span></code>)
only the <code class="computeroutput"><span class="special">+</span></code> and <code class="computeroutput"><span class="special">*</span></code> operators are required. If, however,
a controlled stepper is used one also needs to specify the division operator
<code class="computeroutput"><span class="special">/</span></code> because calculation of
the error term involves an element wise division of the state types.
Additionally, controlled steppers require an <code class="computeroutput"><span class="identifier">abs</span></code>
function calculating the element-wise absolute value for the state type:
</p>
<p>
</p>
<pre class="programlisting"><span class="comment">// only required for steppers with error control</span>
<span class="identifier">point3D</span> <span class="keyword">operator</span><span class="special">/(</span> <span class="keyword">const</span> <span class="identifier">point3D</span> <span class="special">&amp;</span><span class="identifier">p1</span> <span class="special">,</span> <span class="keyword">const</span> <span class="identifier">point3D</span> <span class="special">&amp;</span><span class="identifier">p2</span> <span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">point3D</span><span class="special">(</span> <span class="identifier">p1</span><span class="special">.</span><span class="identifier">x</span><span class="special">/</span><span class="identifier">p2</span><span class="special">.</span><span class="identifier">x</span> <span class="special">,</span> <span class="identifier">p1</span><span class="special">.</span><span class="identifier">y</span><span class="special">/</span><span class="identifier">p2</span><span class="special">.</span><span class="identifier">y</span> <span class="special">,</span> <span class="identifier">p1</span><span class="special">.</span><span class="identifier">z</span><span class="special">/</span><span class="identifier">p1</span><span class="special">.</span><span class="identifier">z</span> <span class="special">);</span>
<span class="special">}</span>
<span class="identifier">point3D</span> <span class="identifier">abs</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">point3D</span> <span class="special">&amp;</span><span class="identifier">p</span> <span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">point3D</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">abs</span><span class="special">(</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">x</span><span class="special">)</span> <span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">abs</span><span class="special">(</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">y</span><span class="special">)</span> <span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">abs</span><span class="special">(</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">z</span><span class="special">)</span> <span class="special">);</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
Finally, we have to provide a specialization to calculate the infintity
norm of a state:
</p>
<p>
</p>
<pre class="programlisting"><span class="comment">// also only for steppers with error control</span>
<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">numeric</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">odeint</span> <span class="special">{</span>
<span class="keyword">template</span><span class="special">&lt;&gt;</span>
<span class="keyword">struct</span> <span class="identifier">vector_space_norm_inf</span><span class="special">&lt;</span> <span class="identifier">point3D</span> <span class="special">&gt;</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="keyword">double</span> <span class="identifier">result_type</span><span class="special">;</span>
<span class="keyword">double</span> <span class="keyword">operator</span><span class="special">()(</span> <span class="keyword">const</span> <span class="identifier">point3D</span> <span class="special">&amp;</span><span class="identifier">p</span> <span class="special">)</span> <span class="keyword">const</span>
<span class="special">{</span>
<span class="keyword">using</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">max</span><span class="special">;</span>
<span class="keyword">using</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">abs</span><span class="special">;</span>
<span class="keyword">return</span> <span class="identifier">max</span><span class="special">(</span> <span class="identifier">max</span><span class="special">(</span> <span class="identifier">abs</span><span class="special">(</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">x</span> <span class="special">)</span> <span class="special">,</span> <span class="identifier">abs</span><span class="special">(</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">y</span> <span class="special">)</span> <span class="special">)</span> <span class="special">,</span> <span class="identifier">abs</span><span class="special">(</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">z</span> <span class="special">)</span> <span class="special">);</span>
<span class="special">}</span>
<span class="special">};</span>
<span class="special">}</span> <span class="special">}</span> <span class="special">}</span>
</pre>
<p>
</p>
<p>
Again, note that the two last steps were only required if you want to
use controlled steppers. For simple steppers definition of the simple
<code class="computeroutput"><span class="special">+=</span></code> and <code class="computeroutput"><span class="special">*=</span></code>
operators are sufficient. Having defined such a point type, we can easily
perform the integration on a Lorenz system by explicitely configuring
the <code class="computeroutput"><span class="identifier">vector_space_algebra</span></code>
in the stepper's template argument list:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">const</span> <span class="keyword">double</span> <span class="identifier">sigma</span> <span class="special">=</span> <span class="number">10.0</span><span class="special">;</span>
<span class="keyword">const</span> <span class="keyword">double</span> <span class="identifier">R</span> <span class="special">=</span> <span class="number">28.0</span><span class="special">;</span>
<span class="keyword">const</span> <span class="keyword">double</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">8.0</span> <span class="special">/</span> <span class="number">3.0</span><span class="special">;</span>
<span class="keyword">void</span> <span class="identifier">lorenz</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">point3D</span> <span class="special">&amp;</span><span class="identifier">x</span> <span class="special">,</span> <span class="identifier">point3D</span> <span class="special">&amp;</span><span class="identifier">dxdt</span> <span class="special">,</span> <span class="keyword">const</span> <span class="keyword">double</span> <span class="identifier">t</span> <span class="special">)</span>
<span class="special">{</span>
<span class="identifier">dxdt</span><span class="special">.</span><span class="identifier">x</span> <span class="special">=</span> <span class="identifier">sigma</span> <span class="special">*</span> <span class="special">(</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">y</span> <span class="special">-</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">x</span> <span class="special">);</span>
<span class="identifier">dxdt</span><span class="special">.</span><span class="identifier">y</span> <span class="special">=</span> <span class="identifier">R</span> <span class="special">*</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">x</span> <span class="special">-</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">y</span> <span class="special">-</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">x</span> <span class="special">*</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">z</span><span class="special">;</span>
<span class="identifier">dxdt</span><span class="special">.</span><span class="identifier">z</span> <span class="special">=</span> <span class="special">-</span><span class="identifier">b</span> <span class="special">*</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">z</span> <span class="special">+</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">x</span> <span class="special">*</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">y</span><span class="special">;</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">numeric</span><span class="special">::</span><span class="identifier">odeint</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="identifier">point3D</span> <span class="identifier">x</span><span class="special">(</span> <span class="number">10.0</span> <span class="special">,</span> <span class="number">5.0</span> <span class="special">,</span> <span class="number">5.0</span> <span class="special">);</span>
<span class="comment">// point type defines it's own operators -&gt; use vector_space_algebra !</span>
<span class="keyword">typedef</span> <span class="identifier">runge_kutta_dopri5</span><span class="special">&lt;</span> <span class="identifier">point3D</span> <span class="special">,</span> <span class="keyword">double</span> <span class="special">,</span> <span class="identifier">point3D</span> <span class="special">,</span>
<span class="keyword">double</span> <span class="special">,</span> <span class="identifier">vector_space_algebra</span> <span class="special">&gt;</span> <span class="identifier">stepper</span><span class="special">;</span>
<span class="keyword">int</span> <span class="identifier">steps</span> <span class="special">=</span> <span class="identifier">integrate_adaptive</span><span class="special">(</span> <span class="identifier">make_controlled</span><span class="special">&lt;</span><span class="identifier">stepper</span><span class="special">&gt;(</span> <span class="number">1E-10</span> <span class="special">,</span> <span class="number">1E-10</span> <span class="special">)</span> <span class="special">,</span> <span class="identifier">lorenz</span> <span class="special">,</span> <span class="identifier">x</span> <span class="special">,</span>
<span class="number">0.0</span> <span class="special">,</span> <span class="number">10.0</span> <span class="special">,</span> <span class="number">0.1</span> <span class="special">);</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">x</span> <span class="special">&lt;&lt;</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">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"steps: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">steps</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
The whole example can be found in <a href="https://github.com/headmyshoulder/odeint-v2/blob/master/examples/lorenz_point.cpp" target="_top">lorenz_point.cpp</a>
</p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
For the most <code class="computeroutput"><span class="identifier">state_types</span></code>,
odeint is able to automatically determine the correct algebra and operations.
But if you want to use your own <code class="computeroutput"><span class="identifier">state_type</span></code>,
as in this example with <code class="computeroutput"><span class="identifier">point3D</span></code>,
you have to manually configure the right algebra/operations, unless
your <code class="computeroutput"><span class="identifier">state_type</span></code> works
with the default choice of <code class="computeroutput"><span class="identifier">range_algebra</span></code>
and <code class="computeroutput"><span class="identifier">default_operations</span></code>.
</p></td></tr>
</table></div>
</div>
</div>
<p>
gsl_vector, gsl_matrix, ublas::matrix, blitz::matrix, thrust
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.adapt_your_own_operations"></a><a class="link" href="state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.adapt_your_own_operations" title="Adapt your own operations">Adapt
your own operations</a>
</h4></div></div></div>
<p>
to be continued
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
thrust
</li>
<li class="listitem">
gsl_complex
</li>
<li class="listitem">
min, max, pow
</li>
</ul></div>
</div>
</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 &#169; 2009-2012 Karsten
Ahnert and Mario Mulansky<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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