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<section id="writing-an-algorithm">
<span id="writinganalgorithm"></span><h1>Writing An Algorithm<a class="headerlink" href="#writing-an-algorithm" title="Link to this heading">#</a></h1>
<section id="introduction">
<h2>Introduction<a class="headerlink" href="#introduction" title="Link to this heading">#</a></h2>
<p>Mantid’s <a class="reference external" href="https://docs.mantidproject.org/nightly/concepts/Plugin.html#plugin" title="(in MantidProject v6.15)"><span class="xref std std-ref">plugin</span></a> architecture has been engineered so that it is easy for a developer, or intrepid user, to write an algorithm.
This page is a primer for the user about to write their first algorithm and assumes no great knowledge of C++.
It covers the basics, with links to more advanced options where appropriate.
There is special description for the case when you are looking to add a custom <a class="reference internal" href="WritingCustomConvertToMDTransformation.html#writingcustomconverttomdtransformation"><span class="std std-ref">MD conversion plugin</span></a>.</p>
<p>Alternatively, you can implement your algorithm in <a class="reference external" href="https://docs.mantidproject.org/nightly/tutorials/extending_mantid_with_python/index.html#emwp-intro" title="(in MantidProject v6.15)"><span class="xref std std-ref">Python</span></a>.
Prototyping your algorithm in Python can be faster with features like hot-reloading.
See <a class="reference internal" href="PythonVSCppAlgorithms.html#pythonvscppalgorithms"><span class="std std-ref">Python Vs C++ Algorithms</span></a> for a comparison of Mantid’s two programming languages.</p>
<p>All <a class="reference external" href="https://docs.mantidproject.org/nightly/algorithms/index.html#algorithms-list" title="(in MantidProject v6.15)"><span class="xref std std-ref">algorithms</span></a> in Mantid <a class="reference external" href="http://en.wikipedia.org/wiki/Inheritance_(computer_science)">inherit</a> from a base <code class="docutils literal notranslate"><span class="pre">Algorithm</span></code> class,
which provides the support and services required for running a specific algorithm and greatly simplifies the process of writing a new one.</p>
</section>
<section id="getting-started">
<h2>Getting Started<a class="headerlink" href="#getting-started" title="Link to this heading">#</a></h2>
<p>Creating a new algorithm is simplified using <a class="reference internal" href="ToolsOverview.html#class-maker-py"><span class="std std-ref">class_maker.py</span></a></p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>$<span class="w"> </span>python<span class="w"> </span>buildconfig/class_maker.py<span class="w"> </span>--alg<span class="w"> </span>Algorithms<span class="w"> </span>MyAlg
</pre></div>
</div>
<p>which will give an amount of information about all that it did.
The intentionally failing unit test, <code class="docutils literal notranslate"><span class="pre">MyAlgTest.h</span></code>, and user docs, <code class="docutils literal notranslate"><span class="pre">MyAlg-v1.rst</span></code>, will not be described here, but need to be updated before contributing.
The excerpts below are the files created and formatted using the <code class="docutils literal notranslate"><span class="pre">pre-commit</span></code> hooks configured for c++ files.
The exact contents of the generated code may change, the methods required do not.</p>
<p><strong>Header file</strong> <a class="reference download internal" download="" href="_downloads/a9fd095f1c23924a169b2df1ceda0a1d/MyAlg_initial.h"><code class="xref download docutils literal notranslate"><span class="pre">MyAlg_initial.h</span></code></a> from <code class="docutils literal notranslate"><span class="pre">class_maker.py</span></code></p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos"> 1</span><span class="cp">#pragma once</span>
<span class="linenos"> 2</span>
<span class="linenos"> 3</span><span class="cp">#include</span><span class="w"> </span><span class="cpf">"MantidAPI/Algorithm.h"</span>
<span class="linenos"> 4</span><span class="cp">#include</span><span class="w"> </span><span class="cpf">"MantidAlgorithms/DllConfig.h"</span>
<span class="linenos"> 5</span>
<span class="linenos"> 6</span><span class="k">namespace</span><span class="w"> </span><span class="nn">Mantid</span><span class="w"> </span><span class="p">{</span>
<span class="linenos"> 7</span><span class="k">namespace</span><span class="w"> </span><span class="nn">Algorithms</span><span class="w"> </span><span class="p">{</span>
<span class="linenos"> 8</span>
<span class="linenos"> 9</span><span class="cm">/** MyAlg : TODO: DESCRIPTION</span>
<span class="linenos">10</span><span class="cm"> */</span>
<span class="linenos">11</span><span class="k">class</span><span class="w"> </span><span class="nc">MANTID_ALGORITHMS_DLL</span><span class="w"> </span><span class="n">MyAlg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="k">public</span><span class="w"> </span><span class="n">API</span><span class="o">::</span><span class="n">Algorithm</span><span class="w"> </span><span class="p">{</span>
<span class="linenos">12</span><span class="k">public</span><span class="o">:</span>
<span class="linenos">13</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">name</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="k">override</span><span class="p">;</span>
<span class="linenos">14</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">version</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="k">override</span><span class="p">;</span>
<span class="linenos">15</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="nf">category</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="k">override</span><span class="p">;</span>
<span class="linenos">16</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="nf">summary</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="k">override</span><span class="p">;</span>
<span class="linenos">17</span>
<span class="linenos">18</span><span class="k">private</span><span class="o">:</span>
<span class="linenos">19</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">init</span><span class="p">()</span><span class="w"> </span><span class="k">override</span><span class="p">;</span>
<span class="linenos">20</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">exec</span><span class="p">()</span><span class="w"> </span><span class="k">override</span><span class="p">;</span>
<span class="linenos">21</span><span class="p">};</span>
<span class="linenos">22</span>
<span class="linenos">23</span><span class="p">}</span><span class="w"> </span><span class="c1">// namespace Algorithms</span>
<span class="linenos">24</span><span class="p">}</span><span class="w"> </span><span class="c1">// namespace Mantid</span>
</pre></div>
</div>
<p><strong>Source file</strong> <a class="reference download internal" download="" href="_downloads/f7122a6b15263092b9a93a440568f3ba/MyAlg_initial.cpp"><code class="xref download docutils literal notranslate"><span class="pre">MyAlg_initial.cpp</span></code></a> from <code class="docutils literal notranslate"><span class="pre">class_maker.py</span></code></p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos"> 8</span><span class="cp">#include</span><span class="w"> </span><span class="cpf">"MantidAlgorithms/MyAlg.h"</span>
<span class="linenos"> 9</span>
<span class="linenos">10</span><span class="k">namespace</span><span class="w"> </span><span class="nn">Mantid</span><span class="w"> </span><span class="p">{</span>
<span class="linenos">11</span><span class="k">namespace</span><span class="w"> </span><span class="nn">Algorithms</span><span class="w"> </span><span class="p">{</span>
<span class="linenos">12</span><span class="k">using</span><span class="w"> </span><span class="n">Mantid</span><span class="o">::</span><span class="n">API</span><span class="o">::</span><span class="n">WorkspaceProperty</span><span class="p">;</span>
<span class="linenos">13</span><span class="k">using</span><span class="w"> </span><span class="n">Mantid</span><span class="o">::</span><span class="n">Kernel</span><span class="o">::</span><span class="n">Direction</span><span class="p">;</span>
<span class="linenos">14</span>
<span class="linenos">15</span><span class="c1">// Register the algorithm into the AlgorithmFactory</span>
<span class="linenos">16</span><span class="n">DECLARE_ALGORITHM</span><span class="p">(</span><span class="n">MyAlg</span><span class="p">)</span>
<span class="linenos">17</span>
<span class="linenos">18</span><span class="c1">//----------------------------------------------------------------------------------------------</span>
<span class="linenos">19</span>
<span class="linenos">20</span><span class="c1">/// Algorithms name for identification. @see Algorithm::name</span>
<span class="linenos">21</span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">MyAlg</span><span class="o">::</span><span class="n">name</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="s">"MyAlg"</span><span class="p">;</span><span class="w"> </span><span class="p">}</span>
<span class="linenos">22</span>
<span class="linenos">23</span><span class="c1">/// Algorithm's version for identification. @see Algorithm::version</span>
<span class="linenos">24</span><span class="kt">int</span><span class="w"> </span><span class="n">MyAlg</span><span class="o">::</span><span class="n">version</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="p">}</span>
<span class="linenos">25</span>
<span class="linenos">26</span><span class="c1">/// Algorithm's category for identification. @see Algorithm::category</span>
<span class="linenos">27</span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">MyAlg</span><span class="o">::</span><span class="n">category</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="s">"TODO: FILL IN A CATEGORY"</span><span class="p">;</span><span class="w"> </span><span class="p">}</span>
<span class="linenos">28</span>
<span class="linenos">29</span><span class="c1">/// Algorithm's summary for use in the GUI and help. @see Algorithm::summary</span>
<span class="linenos">30</span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">MyAlg</span><span class="o">::</span><span class="n">summary</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="s">"TODO: FILL IN A SUMMARY"</span><span class="p">;</span><span class="w"> </span><span class="p">}</span>
<span class="linenos">31</span>
<span class="linenos">32</span><span class="c1">//----------------------------------------------------------------------------------------------</span>
<span class="linenos">33</span><span class="cm">/** Initialize the algorithm's properties.</span>
<span class="linenos">34</span><span class="cm"> */</span>
<span class="linenos">35</span><span class="kt">void</span><span class="w"> </span><span class="n">MyAlg</span><span class="o">::</span><span class="n">init</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="linenos">36</span><span class="w"> </span><span class="n">declareProperty</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">make_unique</span><span class="o"><</span><span class="n">WorkspaceProperty</span><span class="o"><</span><span class="n">API</span><span class="o">::</span><span class="n">Workspace</span><span class="o">>></span><span class="p">(</span><span class="s">"InputWorkspace"</span><span class="p">,</span><span class="w"> </span><span class="s">""</span><span class="p">,</span><span class="w"> </span><span class="n">Direction</span><span class="o">::</span><span class="n">Input</span><span class="p">),</span>
<span class="linenos">37</span><span class="w"> </span><span class="s">"An input workspace."</span><span class="p">);</span>
<span class="linenos">38</span><span class="w"> </span><span class="n">declareProperty</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">make_unique</span><span class="o"><</span><span class="n">WorkspaceProperty</span><span class="o"><</span><span class="n">API</span><span class="o">::</span><span class="n">Workspace</span><span class="o">>></span><span class="p">(</span><span class="s">"OutputWorkspace"</span><span class="p">,</span><span class="w"> </span><span class="s">""</span><span class="p">,</span><span class="w"> </span><span class="n">Direction</span><span class="o">::</span><span class="n">Output</span><span class="p">),</span>
<span class="linenos">39</span><span class="w"> </span><span class="s">"An output workspace."</span><span class="p">);</span>
<span class="linenos">40</span><span class="p">}</span>
<span class="linenos">41</span>
<span class="linenos">42</span><span class="c1">//----------------------------------------------------------------------------------------------</span>
<span class="linenos">43</span><span class="cm">/** Execute the algorithm.</span>
<span class="linenos">44</span><span class="cm"> */</span>
<span class="linenos">45</span><span class="kt">void</span><span class="w"> </span><span class="n">MyAlg</span><span class="o">::</span><span class="n">exec</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="linenos">46</span><span class="w"> </span><span class="c1">// TODO Auto-generated execute stub</span>
<span class="linenos">47</span><span class="p">}</span>
<span class="linenos">48</span>
<span class="linenos">49</span><span class="p">}</span><span class="w"> </span><span class="c1">// namespace Algorithms</span>
<span class="linenos">50</span><span class="p">}</span><span class="w"> </span><span class="c1">// namespace Mantid</span>
</pre></div>
</div>
<p>At this point you will already have something that will compile and run.
If you then start MantidWorkbench your algorithm will appear in the list of available algorithms and could be run.
Of course, it won’t do anything of interest until you have written some algorithm code.</p>
</section>
<section id="coding-the-algorithm">
<h2>Coding the Algorithm<a class="headerlink" href="#coding-the-algorithm" title="Link to this heading">#</a></h2>
<p>You will see that the algorithm has a variety of methods that need to be filled in.
The example linked here is used throughout the majority of this document.
The first few do not normally change very often</p>
<p>The full files described below are <a class="reference download internal" download="" href="_downloads/24fa3dc42bde5b52bdab6565e2b45f23/MyAlg.h"><code class="xref download docutils literal notranslate"><span class="pre">MyAlg.h</span></code></a> and <a class="reference download internal" download="" href="_downloads/627c11e75c9e793bc87cb9ee2edd80ed/MyAlg.cpp"><code class="xref download docutils literal notranslate"><span class="pre">MyAlg.cpp</span></code></a>.
Only <code class="docutils literal notranslate"><span class="pre">MyAlg.cpp</span></code> will be shown in detail, but both are functional code that can be viewed as “simple” examples.</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">28</span><span class="c1">/// Algorithms name for identification. @see Algorithm::name</span>
<span class="linenos">29</span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="nf">MyAlg::name</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="s">"MyAlg"</span><span class="p">;</span><span class="w"> </span><span class="p">}</span>
<span class="linenos">30</span>
<span class="linenos">31</span><span class="c1">/// Algorithm's version for identification. @see Algorithm::version</span>
<span class="linenos">32</span><span class="kt">int</span><span class="w"> </span><span class="nf">MyAlg::version</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="p">}</span>
<span class="linenos">33</span>
<span class="linenos">34</span><span class="c1">/// Algorithm's category for identification. @see Algorithm::category</span>
<span class="linenos">35</span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="nf">MyAlg::category</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="s">"Examples"</span><span class="p">;</span><span class="w"> </span><span class="p">}</span>
<span class="linenos">36</span>
<span class="linenos">37</span><span class="c1">/// Algorithm's summary for use in the GUI and help. @see Algorithm::summary</span>
<span class="linenos">38</span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="nf">MyAlg::summary</span><span class="p">()</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="s">"Multiplies a workspace by a constant. There are some modes"</span><span class="p">;</span><span class="w"> </span><span class="p">}</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">name()</span></code> method should not be verified.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">version()</span></code> method normally returns <code class="docutils literal notranslate"><span class="pre">1</span></code>.
Mantid allows for having multiple versions of an algorithm registered which is facilitated by this method.
The most common use cases for multiple versions are when the signature or underly assumptions are radically changed.
Overall, few algorithms have more than one “version.”</p>
<p>The <code class="docutils literal notranslate"><span class="pre">category()</span></code> method aids users in finding the algorithm.
The return can be a semilcolon (<code class="docutils literal notranslate"><span class="pre">;</span></code>) delimited string of categors/subcategories.
You are highly encouraged to stay to the list of <a class="reference external" href="https://docs.mantidproject.org/nightly/algorithms/index.html#algorithms-list" title="(in MantidProject v6.15)"><span class="xref std std-ref">existing categories</span></a>.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">summary()</span></code> method is a brief description of the algorithms functionality.
It is automatically re-used in the python docstring, and the generated help.
The first sentence of the summary (up to the first period, <code class="docutils literal notranslate"><span class="pre">.</span></code>) is what appears in the generated gui for the algorithm.</p>
<p>You will see that the algorithm skeletons set up in the last section contain two larger methods called <code class="docutils literal notranslate"><span class="pre">init</span></code> and <code class="docutils literal notranslate"><span class="pre">exec</span></code>.
These are described in sections below.</p>
<section id="logging">
<h3>Logging<a class="headerlink" href="#logging" title="Link to this heading">#</a></h3>
<p>The algorithm base class defines an object, <code class="docutils literal notranslate"><span class="pre">g_log</span></code>.
The <code class="docutils literal notranslate"><span class="pre">g_log</span></code> object enables access to the <a class="reference internal" href="Logging.html#logging"><span class="std std-ref">logging</span></a> facilities of Mantid,
and is an invaluable tool in understanding the running of your algorithms.
When writing information to the logs, be aware of the various levels available and that the default level for users is set to <code class="docutils literal notranslate"><span class="pre">notice</span></code>.</p>
<p>The logging framework does have facility for flushing logs.
However, logging <code class="docutils literal notranslate"><span class="pre">std::endl</span></code> will force the framework to flush at that time and developers should prever <code class="docutils literal notranslate"><span class="pre">"\n"</span></code> instead to not interfere with the framework.</p>
</section>
</section>
<section id="initialization">
<h2>Initialization<a class="headerlink" href="#initialization" title="Link to this heading">#</a></h2>
<p>The <code class="docutils literal notranslate"><span class="pre">init()</span></code> method written in your algorithm is called as part of the larger algorithm lifecycle.
It is a private method that cannot be called directly, but one can call an algorithm’s inherited <code class="docutils literal notranslate"><span class="pre">initialize()</span></code> method for the desired effect.
For details, look at the source of the <a class="reference external" href="https://github.com/mantidproject/mantid/blob/main/Framework/API/src/Algorithm.cpp#L281">API::Algorithm::initialize()</a> .</p>
<p>The initialization (init) method is executed by the <code class="docutils literal notranslate"><span class="pre">FrameworkManager</span></code> when an algorithm is requested and must contain the declaration of the properties required by the algorithm.
Atypically, it can also contain other initialization code such as the calculation of constants used by the algorithm, so long as this does not rely on the values of any of the properties.</p>
<p>Calls to the inherited <code class="docutils literal notranslate"><span class="pre">declareProperty()</span></code> method are used to add a property to this algorithm.
See the properties page for more information on the types of properties supported and the example algorithms in <code class="docutils literal notranslate"><span class="pre">UserAlgorithms</span></code> (especially <a class="reference external" href="https://github.com/mantidproject/mantid/blob/main/Framework/Examples/PropertyAlgorithm.cpp">PropertyAlgorithm</a>
and <a class="reference external" href="https://github.com/mantidproject/mantid/blob/main/Framework/Examples/WorkspaceAlgorithm.cpp">WorkspaceAlgorithm</a>)
for further guidance on how to use them.
There are many overloaded signatures for <code class="docutils literal notranslate"><span class="pre">declareProperty()</span></code> which are intended to make things easier, but can often be confusing due to the many options available.</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">43</span><span class="kt">void</span><span class="w"> </span><span class="nf">MyAlg::init</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="linenos">44</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">instrumentValidator</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">CompositeValidator</span><span class="o">></span><span class="p">();</span>
<span class="linenos">45</span><span class="w"> </span><span class="n">instrumentValidator</span><span class="o">-></span><span class="n">add</span><span class="o"><</span><span class="n">InstrumentValidator</span><span class="o">></span><span class="p">();</span>
<span class="linenos">46</span><span class="w"> </span><span class="n">declareProperty</span><span class="p">(</span>
<span class="linenos">47</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_unique</span><span class="o"><</span><span class="n">WorkspaceProperty</span><span class="o"><</span><span class="n">MatrixWorkspace</span><span class="o">>></span><span class="p">(</span><span class="s">"InputWorkspace"</span><span class="p">,</span><span class="w"> </span><span class="s">""</span><span class="p">,</span><span class="w"> </span><span class="n">Direction</span><span class="o">::</span><span class="n">Input</span><span class="p">,</span><span class="w"> </span><span class="n">instrumentValidator</span><span class="p">),</span>
<span class="linenos">48</span><span class="w"> </span><span class="s">"An input workspace."</span><span class="p">);</span>
<span class="linenos">49</span><span class="w"> </span><span class="n">declareProperty</span><span class="p">(</span><span class="s">"NumberToApply"</span><span class="p">,</span><span class="w"> </span><span class="n">EMPTY_DBL</span><span class="p">(),</span><span class="w"> </span><span class="s">"Value to apply to workspace. This is extra information"</span><span class="p">);</span>
<span class="linenos">50</span>
<span class="linenos">51</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">propOptions</span><span class="p">{</span><span class="s">"X"</span><span class="p">,</span><span class="w"> </span><span class="s">"Y"</span><span class="p">};</span>
<span class="linenos">52</span><span class="w"> </span><span class="n">declareProperty</span><span class="p">(</span><span class="s">"WayToApply"</span><span class="p">,</span><span class="w"> </span><span class="n">propOptions</span><span class="p">.</span><span class="n">back</span><span class="p">(),</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">StringListValidator</span><span class="o">></span><span class="p">(</span><span class="n">propOptions</span><span class="p">),</span>
<span class="linenos">53</span><span class="w"> </span><span class="s">"Which axis to apply values to"</span><span class="p">);</span>
<span class="linenos">54</span>
<span class="linenos">55</span><span class="w"> </span><span class="n">declareProperty</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">make_unique</span><span class="o"><</span><span class="n">WorkspaceProperty</span><span class="o"><</span><span class="n">MatrixWorkspace</span><span class="o">>></span><span class="p">(</span><span class="s">"OutputWorkspace"</span><span class="p">,</span><span class="w"> </span><span class="s">""</span><span class="p">,</span><span class="w"> </span><span class="n">Direction</span><span class="o">::</span><span class="n">Output</span><span class="p">),</span>
<span class="linenos">56</span><span class="w"> </span><span class="s">"An output workspace."</span><span class="p">);</span>
<span class="linenos">57</span><span class="p">}</span>
</pre></div>
</div>
<p>This example shows a couple of different ways of declaring properites.
They all have a couple of features in common:</p>
<ul class="simple">
<li><p>Every property has a name. Here they are <code class="docutils literal notranslate"><span class="pre">InputWorkspace</span></code>, <code class="docutils literal notranslate"><span class="pre">NumberToApply</span></code>, <code class="docutils literal notranslate"><span class="pre">WayToApply</span></code>, and <code class="docutils literal notranslate"><span class="pre">OutputWorkspace</span></code></p></li>
<li><p>Every property has a default value, many of which are effectively empty.
Here they are empty workspace name, <code class="docutils literal notranslate"><span class="pre">EMPTY_DBL()</span></code> (special float value), <code class="docutils literal notranslate"><span class="pre">"Y"</span></code>, and empty name.
It is extremely unusual to specify a default workspace name</p></li>
<li><p>Every property has documentation.
Most of the ones here are very uniformative, but the document on <code class="docutils literal notranslate"><span class="pre">NumberToApply</span></code> was written to demonstrate a particular point.
Everything up to the first period (<code class="docutils literal notranslate"><span class="pre">.</span></code>) appears in the mouseover in the generated algorithm dialogs.
The whole string appears in the user docs and python help.</p></li>
</ul>
<p>An optional <a class="reference external" href="https://docs.mantidproject.org/nightly/api/python/mantid/kernel/Property.html#properties-validators" title="(in MantidProject v6.15)"><span class="xref std std-ref">validator</span></a> or <a class="reference external" href="https://docs.mantidproject.org/nightly/api/python/mantid/kernel/Property.html#properties-directions" title="(in MantidProject v6.15)"><span class="xref std std-ref">directional argument</span></a> (input, output or both) can also be appended.
The syntax for other property types (<code class="docutils literal notranslate"><span class="pre">WorkspaceProperty</span></code> and <code class="docutils literal notranslate"><span class="pre">ArrayProperty</span></code>) is more complex - see the <a class="reference external" href="https://docs.mantidproject.org/nightly/api/python/mantid/kernel/Property.html#mantid-kernel-property" title="(in MantidProject v6.15)"><span class="xref std std-ref">properties</span></a> page.</p>
<section id="validation-of-inputs">
<h3>Validation of inputs<a class="headerlink" href="#validation-of-inputs" title="Link to this heading">#</a></h3>
<p>While not part of the initialization, the optional <code class="docutils literal notranslate"><span class="pre">validateInputs()</span></code> method allows for cross-checking parameters.
This particular example shows how one would ban a particular value, but normally a validator would be placed on the property itself for this behavior
For more advanced validation, override the <code class="docutils literal notranslate"><span class="pre">Algorithm::validateInputs()</span></code> method.
This is a method that returns a map where:</p>
<ul class="simple">
<li><p>The key is the name of the property that is in error.</p></li>
<li><p>The value is a string describing the error.</p></li>
</ul>
<p>This method allows you to provide validation that depends on several property values at once (something that cannot be done with <code class="docutils literal notranslate"><span class="pre">IValidator</span></code>).
Its default implementation returns an empty map, signifying no errors.</p>
<p>It will be called in dialogs <strong>after</strong> parsing all inputs and setting the properties,
but <strong>before</strong> executing.
It is also called again in the <code class="docutils literal notranslate"><span class="pre">execute()</span></code> call, which will throw if this returns something.</p>
<p>This will set a “star” <code class="docutils literal notranslate"><span class="pre">*</span></code> label next to each property that is reporting an error.
This makes it easier for users to find where they went wrong.</p>
<p>If your <code class="docutils literal notranslate"><span class="pre">validateInputs()</span></code> method validates an input workspace property,
bear in mind that the user could provide a <code class="docutils literal notranslate"><span class="pre">WorkspaceGroup</span></code> (or an unexpected type of workspace) - when retrieving the property,
check that casting it to its intended type succeeded before attempting to use it.</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">58</span><span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">MyAlg</span><span class="o">::</span><span class="n">validateInputs</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="linenos">59</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">issues</span><span class="p">;</span>
<span class="linenos">60</span>
<span class="linenos">61</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">isDefault</span><span class="p">(</span><span class="s">"NumberToApply"</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
<span class="linenos">62</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="n">value</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">getProperty</span><span class="p">(</span><span class="s">"NumberToApply"</span><span class="p">);</span>
<span class="linenos">63</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">value</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">42.</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="linenos">64</span><span class="w"> </span><span class="n">issues</span><span class="p">[</span><span class="s">"NumberToApply"</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"We do cannot answer that question"</span><span class="p">;</span>
<span class="linenos">65</span><span class="w"> </span><span class="p">}</span>
<span class="linenos">66</span><span class="w"> </span><span class="p">}</span>
<span class="linenos">67</span>
<span class="linenos">68</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">issues</span><span class="p">;</span>
<span class="linenos">69</span><span class="p">}</span>
</pre></div>
</div>
</section>
</section>
<section id="execution">
<h2>Execution<a class="headerlink" href="#execution" title="Link to this heading">#</a></h2>
<p>Like initialization, the <code class="docutils literal notranslate"><span class="pre">exec()</span></code> method you write is not directly, but can be indirectly called via the <code class="docutils literal notranslate"><span class="pre">execute()</span></code> method of the algorith
There are other methods that will do the same thing in different modes.
All of them eventually call the <a class="reference external" href="https://github.com/mantidproject/mantid/blob/main/Framework/API/src/Algorithm.cpp#L509">API::Algorithm::executeInternal()</a> which does the following</p>
<ul class="simple">
<li><p>log a warning message if the algorithm is marked as deprecated</p></li>
<li><p>validate all of the input parameters individually against what they are set to checking for type and any validators that were defined</p></li>
<li><p>run the <code class="docutils literal notranslate"><span class="pre">validateInputs()</span></code> method</p></li>
<li><p>run the <code class="docutils literal notranslate"><span class="pre">exec()</span></code> method</p></li>
<li><p>add history to the Workspace annotating the parameters that the algorithm was called with</p></li>
</ul>
<p>Additionally, the algorithm framework also handles things like sync/async calling, exception handling, and interaction with <a class="reference external" href="https://docs.mantidproject.org/nightly/api/python/mantid/api/AnalysisDataServiceImpl.html#mantid-api-analysisdataserviceimpl" title="(in MantidProject v6.15)"><span class="xref std std-ref">AnalysisDataService</span></a>.</p>
<section id="fetching-properties">
<h3>Fetching properties<a class="headerlink" href="#fetching-properties" title="Link to this heading">#</a></h3>
<p>Before the data can be processed,
the first task is likely to be to fetch the values of the input properties.
This uses the <code class="docutils literal notranslate"><span class="pre">getProperty()</span></code> method as follows</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">76</span><span class="w"> </span><span class="n">API</span><span class="o">::</span><span class="n">MatrixWorkspace_sptr</span><span class="w"> </span><span class="n">inputWS</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">getProperty</span><span class="p">(</span><span class="s">"InputWorkspace"</span><span class="p">);</span>
<span class="linenos">77</span><span class="w"> </span><span class="n">API</span><span class="o">::</span><span class="n">MatrixWorkspace_sptr</span><span class="w"> </span><span class="n">outputWS</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">getProperty</span><span class="p">(</span><span class="s">"OutputWorkspace"</span><span class="p">);</span>
<span class="linenos">78</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="n">number</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">getProperty</span><span class="p">(</span><span class="s">"NumberToApply"</span><span class="p">);</span>
<span class="linenos">79</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">axisToApply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">getPropertyValue</span><span class="p">(</span><span class="s">"WayToApply"</span><span class="p">);</span>
</pre></div>
</div>
<p>where the type in the left hand side is the type of the property (<code class="docutils literal notranslate"><span class="pre">int</span></code>, <code class="docutils literal notranslate"><span class="pre">double</span></code>, <code class="docutils literal notranslate"><span class="pre">std::string</span></code>, <code class="docutils literal notranslate"><span class="pre">std::vector</span></code>…) and must match what was defined in the <code class="docutils literal notranslate"><span class="pre">init()</span></code>.
Note that the value of a <code class="docutils literal notranslate"><span class="pre">WorkspaceProperty</span></code> is a <a class="reference external" href="https://docs.mantidproject.org/nightly/concepts/SharedPointer.html#shared-pointer" title="(in MantidProject v6.15)"><span class="xref std std-ref">shared pointer</span></a> to the workspace,
which is referred to as <code class="docutils literal notranslate"><span class="pre">Mantid::API::Workspace_sptr</span></code> or <code class="docutils literal notranslate"><span class="pre">Mantid::API::Workspace_const_sptr</span></code>.
The latter should be used for input workspaces that will not need to be changed in the course of the algorithm.
The output workspace is retrieved here to be used to detect if the algorithm is being performed in-place which will be discussed further down in this document.
This example also uses the <code class="docutils literal notranslate"><span class="pre">getPropertyValue()</span></code> method which returns a string representation of the requested property (e.g. the name of the workspace).</p>
<p>If a handle is required on the property itself, rather than just its value, then the same method is used as follows:</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">Mantid</span><span class="o">::</span><span class="n">Kernel</span><span class="o">::</span><span class="n">Property</span><span class="o">*</span><span class="w"> </span><span class="n">myProperty</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">getProperty</span><span class="p">(</span><span class="s">"PropertyName"</span><span class="p">);</span>
</pre></div>
</div>
<p>This is useful, for example, for checking whether or not an optional property has been set (using Property’s <code class="docutils literal notranslate"><span class="pre">isDefault()</span></code> method).
However, the algorithm has a convenience method <code class="docutils literal notranslate"><span class="pre">isDefault(const</span> <span class="pre">std::string</span> <span class="pre">&)</span></code> as well.</p>
</section>
<section id="creating-the-output-workspace">
<h3>Creating the output workspace<a class="headerlink" href="#creating-the-output-workspace" title="Link to this heading">#</a></h3>
<p>Usually, the result of an algorithm will be stored in another new workspace and the algorithm
will need to create that new workspace through a call to the <code class="docutils literal notranslate"><span class="pre">WorkspaceFactory</span></code>.
For the (common) example where the output workspace should be of the same type and size as the input one, the code would read as follows:</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">outputWS</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mantid</span><span class="o">::</span><span class="n">API</span><span class="o">::</span><span class="n">WorkspaceFactory</span><span class="o">::</span><span class="n">Instance</span><span class="p">().</span><span class="n">create</span><span class="p">(</span><span class="n">inputWS</span><span class="p">);</span>
</pre></div>
</div>
<p>where <code class="docutils literal notranslate"><span class="pre">inputWS</span></code> is a shared pointer to the input workspace.
However, in many instances, one can simply clone the input workspace and work on the clone directly.</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">81</span><span class="w"> </span><span class="c1">// set up the output</span>
<span class="linenos">82</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">outputWS</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">inputWS</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="linenos">83</span><span class="w"> </span><span class="n">outputWS</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">inputWS</span><span class="o">-></span><span class="n">clone</span><span class="p">();</span>
<span class="linenos">84</span><span class="w"> </span><span class="p">}</span>
</pre></div>
</div>
<p>It is also important to, at some point, set the output workspace property to point at this workspace.
This is achieved through a call to the <code class="docutils literal notranslate"><span class="pre">setProperty</span></code> method as follows:</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">109</span><span class="w"> </span><span class="c1">// pass back the output workspace</span>
<span class="linenos">110</span><span class="w"> </span><span class="n">setProperty</span><span class="p">(</span><span class="s">"OutputWorkspace"</span><span class="p">,</span><span class="w"> </span><span class="n">outputWS</span><span class="p">);</span>
</pre></div>
</div>
<p>where <code class="docutils literal notranslate"><span class="pre">outputWorkspace</span></code> is a shared pointer to the created output workspace.</p>
</section>
<section id="using-workspaces">
<h3>Using workspaces<a class="headerlink" href="#using-workspaces" title="Link to this heading">#</a></h3>
<p>The bulk of most algorithms will involve the manipulation of the data contained in workspaces and information on how to interact with these is given <a class="reference external" href="https://docs.mantidproject.org/nightly/concepts/WorkingWithWorspaces.html#workingwithworkspaces" title="(in MantidProject v6.15)"><span class="xref std std-ref">here</span></a>.
The more advanced user may also want to refer to the full
<a class="reference external" href="http://doxygen.mantidproject.org/nightly/d3/de9/classMantid_1_1API_1_1Workspace.html">workspace documentation</a>.</p>
<p>Those familiar with C++ should make use of private methods and data members to break up the execution code into more manageable and readable sections.</p>
</section>
</section>
<section id="further-features">
<h2>Further Features<a class="headerlink" href="#further-features" title="Link to this heading">#</a></h2>
<p>The advanced user is referred to the <a class="reference external" href="http://doxygen.mantidproject.org/nightly/d3/de9/classMantid_1_1API_1_1Workspace.html">full documentation page</a>
for the <code class="docutils literal notranslate"><span class="pre">Algorithm</span></code> base class to explore the full range of methods available for use within an algorithm.
A few aspects are highlighted below.</p>
<section id="child-algorithms">
<h3>Child Algorithms<a class="headerlink" href="#child-algorithms" title="Link to this heading">#</a></h3>
<p>Algorithms may wish to make use of the functionality of other algorithms as part of their execution.
For example, if a units change is required the <code class="docutils literal notranslate"><span class="pre">ConvertUnits</span></code> algorithm could be used. Mantid therefore has the concept of a child algorithm and this is accessed through a call to the
<code class="docutils literal notranslate"><span class="pre">createChildAlgorithm</span></code> method as follows:</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">Mantid</span><span class="o">::</span><span class="n">API</span><span class="o">::</span><span class="n">Algorithm_sptr</span><span class="w"> </span><span class="n">childAlg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">createChildAlgorithm</span><span class="p">(</span><span class="s">"AlgorithmName"</span><span class="p">);</span>
</pre></div>
</div>
<p>This call will also initialise the algorithm, so the algorithm’s properties can then be set and it can be executed:</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">childAlg</span><span class="o">-></span><span class="n">setPropertyValue</span><span class="p">(</span><span class="s">"number"</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">);</span>
<span class="n">childAlg</span><span class="o">-></span><span class="n">setProperty</span><span class="o"><</span><span class="n">Workspace_sptr</span><span class="o">></span><span class="p">(</span><span class="s">"Workspace"</span><span class="p">,</span><span class="n">workspacePointer</span><span class="p">);</span>
<span class="n">childAlg</span><span class="o">-></span><span class="n">execute</span><span class="p">();</span>
</pre></div>
</div>
<p>Because <code class="docutils literal notranslate"><span class="pre">Property</span></code> is generic to input <strong>and</strong> output, the workspace pointers cannot be <code class="docutils literal notranslate"><span class="pre">const</span></code> when shared with a child algorithm.</p>
</section>
<section id="workspacegroup-history-from-processgroups">
<h3>WorkspaceGroup history from processGroups<a class="headerlink" href="#workspacegroup-history-from-processgroups" title="Link to this heading">#</a></h3>
<p>When an algorithm is executed with a <code class="docutils literal notranslate"><span class="pre">WorkspaceGroup</span></code> input, the base <code class="docutils literal notranslate"><span class="pre">Algorithm::processGroups()</span></code> implementation normally executes the algorithm again on each group member.
Those per-member executions record the output workspace history, so the history from the initial group call is not added to the outputs.</p>
<p>Algorithms that override <code class="docutils literal notranslate"><span class="pre">processGroups()</span></code> may need different behaviour.
For example, a group reduction may run a linked workflow across all group members and call child algorithms internally.
In this case the override can opt in to recording the parent algorithm history by calling <code class="docutils literal notranslate"><span class="pre">enableHistoryRecordingForProcessGroups(true)</span></code>:</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="kt">bool</span><span class="w"> </span><span class="nf">MyAlgorithm::processGroups</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">m_usingBaseProcessGroups</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span>
<span class="w"> </span><span class="n">enableHistoryRecordingForProcessGroups</span><span class="p">(</span><span class="nb">true</span><span class="p">);</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">child</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">createChildAlgorithm</span><span class="p">(</span><span class="s">"ChildAlgorithm"</span><span class="p">);</span>
<span class="w"> </span><span class="n">child</span><span class="o">-></span><span class="n">setProperty</span><span class="p">(</span><span class="s">"InputWorkspace"</span><span class="p">,</span><span class="w"> </span><span class="n">input</span><span class="p">);</span>
<span class="w"> </span><span class="n">child</span><span class="o">-></span><span class="n">setProperty</span><span class="p">(</span><span class="s">"OutputWorkspace"</span><span class="p">,</span><span class="w"> </span><span class="n">output</span><span class="p">);</span>
<span class="w"> </span><span class="n">child</span><span class="o">-></span><span class="n">execute</span><span class="p">();</span>
<span class="w"> </span><span class="n">setProperty</span><span class="p">(</span><span class="s">"OutputWorkspace"</span><span class="p">,</span><span class="w"> </span><span class="n">output</span><span class="p">);</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<p>This is opt-in only.
Existing <code class="docutils literal notranslate"><span class="pre">processGroups()</span></code> behaviour is unchanged unless the override calls <code class="docutils literal notranslate"><span class="pre">enableHistoryRecordingForProcessGroups(true)</span></code>.
Python algorithms can use the same opt-in by calling <code class="docutils literal notranslate"><span class="pre">self.enableHistoryRecordingForProcessGroups(True)</span></code>.
When the flag is enabled, the parent algorithm is recorded on the output workspaces and any child algorithms run during <code class="docutils literal notranslate"><span class="pre">processGroups()</span></code> remain nested under it in the workspace history.</p>
<p>Keep algorithms that should appear beneath the parent history as child algorithms.
If a child algorithm must still place its output in the <code class="docutils literal notranslate"><span class="pre">AnalysisDataService</span></code>, prefer <code class="docutils literal notranslate"><span class="pre">setAlwaysStoreInADS(true)</span></code> over making it a non-child algorithm with <code class="docutils literal notranslate"><span class="pre">setChild(false)</span></code>.
Running it as non-child creates a separate top-level history entry instead of nesting it under the parent algorithm.</p>
</section>
<section id="enhancing-asynchronous-running">
<h3>Enhancing asynchronous running<a class="headerlink" href="#enhancing-asynchronous-running" title="Link to this heading">#</a></h3>
<p>Any algorithm can be run asynchronously without modification.
However, some features are only enabled if code is added within the <code class="docutils literal notranslate"><span class="pre">exec()</span></code> method.
<code class="docutils literal notranslate"><span class="pre">Algorithm::interruption_point()</span></code> should be called at appropriate intervals so that the algorithm’s execution can be interrupted.
<code class="docutils literal notranslate"><span class="pre">Algorithm::progress(double</span> <span class="pre">p)</span></code> reports the progress of the algorithm.
<code class="docutils literal notranslate"><span class="pre">p</span></code> must be between 0 (start) and 1 (finish).</p>
</section>
<section id="exceptions">
<h3>Exceptions<a class="headerlink" href="#exceptions" title="Link to this heading">#</a></h3>
<p>It is fine to throw exceptions in your algorithms in the event of an unrecoverable failure.
These will be caught in the base Algorithm class, which will report the failure of the algorithm.</p>
</section>
<section id="properties-access-within-workbench-dialogs">
<h3>Properties access within workbench dialogs<a class="headerlink" href="#properties-access-within-workbench-dialogs" title="Link to this heading">#</a></h3>
<p>Once your algorithm is working from a script, and provided it is registered with <code class="docutils literal notranslate"><span class="pre">AlgorithmFactory</span></code>, it will also be possible to execute the algorithm from <code class="docutils literal notranslate"><span class="pre">mantidworkbench</span></code> using the built-in <code class="docutils literal notranslate"><span class="pre">GenericDialog</span></code> feature. To this end there are several <em>optional</em> features available through the use of <code class="docutils literal notranslate"><span class="pre">IPropertySettings</span></code>-derived classes, to enhance the interaction between your algorithm’s properties and the GUI dialog.</p>
<p><code class="docutils literal notranslate"><span class="pre">EnableWhenProperty</span></code>, <code class="docutils literal notranslate"><span class="pre">VisibleWhenProperty</span></code>, and <code class="docutils literal notranslate"><span class="pre">InvisibleProperty</span></code> can be used to hide or disable a property in the GUI dialog panel based on various conditions.</p>
<p><code class="docutils literal notranslate"><span class="pre">SetValueWhenProperty</span></code>, and <code class="docutils literal notranslate"><span class="pre">SetDefaultWhenProperty</span></code> can be used to set the value of a property based on the value of another upstream property, or to emulate the effect of having a property’s <em>default</em> value depend on the value of another property. See <a class="reference internal" href="DynamicProperties.html#dynamicproperties"><span class="std std-ref">Dynamic dialog properties</span></a> for example code showing how to use this feature.</p>
<p>Multiple <code class="docutils literal notranslate"><span class="pre">IPropertySettings</span></code> can be attached to a single property, by applying either the <code class="docutils literal notranslate"><span class="pre">IPropertyManager::setPropertySettings</span></code> method of the algorithm, or the <code class="docutils literal notranslate"><span class="pre">Property::setSettings</span></code> method of the property itself, multiple times. For this reason the property’s <code class="docutils literal notranslate"><span class="pre">getSettings</span></code> method returns a <em>vector</em> of settings, which will be <em>empty</em> in the default no-settings case.</p>
<p>With respect to the property’s enabled and visibility states (on its owner widget), any setting in the vector of settings returning <code class="docutils literal notranslate"><span class="pre">isEnabled</span></code> or <code class="docutils literal notranslate"><span class="pre">isVisible</span></code> values of <code class="docutils literal notranslate"><span class="pre">false</span></code>, results in disabling or hiding the property’s widget. In general, it is expected that only one instance of each of the <code class="docutils literal notranslate"><span class="pre">EnabledWhenProperty</span></code> and <code class="docutils literal notranslate"><span class="pre">VisibleWhenProperty</span></code> settings would be attached to a given property, in combination with any number of instances of other <code class="docutils literal notranslate"><span class="pre">IPropertySettings</span></code>-derived types, although this behavior is not strictly enforced.</p>
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