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<title>Issue 1439: Return from densities() functions?</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#C++11">C++11</a> status.</em></p>
<h3 id="1439"><a href="lwg-defects.html#1439">1439</a>. Return from <code>densities()</code> functions?</h3>
<p><b>Section:</b> 29.5.9.6.2 <a href="https://wg21.link/rand.dist.samp.pconst">[rand.dist.samp.pconst]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#rand.dist.samp.pconst">issues</a> in [rand.dist.samp.pconst].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++11">C++11</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses US-134</b></p>

<p>
These two distributions have a member function called
<code>densities()</code> which returns a <code>vector&lt;double&gt;</code>. The
distribution is templated on <code>RealType</code>. The distribution
also has another member called <code>intervals()</code> which returns
a <code>vector&lt;RealType&gt;</code>. Why doesn't densities return
<code>vector&lt;RealType&gt;</code> as well? If <code>RealType</code> is <code>long double</code>,
the computed densities property isn't being computed to
the precision the client desires. If <code>RealType</code> is <code>float</code>, the
densities vector is taking up twice as much space as the client desires.
</p>

<p><i>[
Resolution proposed by ballot comment:
]</i></p>

<blockquote>
<p>
Change the piecewise constant and linear
distributions to hold / return the densities in a
<code>vector&lt;result_type&gt;</code>.
<p/>
If this is not done, at least correct 29.5.9.6.2 <a href="https://wg21.link/rand.dist.samp.pconst">[rand.dist.samp.pconst]</a> p. 13 which describes
the return of densities as a <code>vector&lt;result_type&gt;</code>.
</p></blockquote>

<p><i>[
Batavia 2010: After reviewing this issue, the working group concurred with the first of the 
suggestions proposed by the NB comment: "Change the piecewise constant and linear distributions 
to hold&#47;return the densities in a vector. "
]</i></p>


<p><i>[
Adopted at 2010-11 Batavia
]</i></p>




<p id="res-1439"><b>Proposed resolution:</b></p>
<ol>
<li>Change 29.5.9.6.2 <a href="https://wg21.link/rand.dist.samp.pconst">[rand.dist.samp.pconst]</a> p. 2, class template <code>piecewise_constant_distribution</code> synopsis
and the prototype description 29.5.9.6.2 <a href="https://wg21.link/rand.dist.samp.pconst">[rand.dist.samp.pconst]</a> before p. 13 as indicated:
<blockquote><pre>
vector&lt;<del>double</del><ins>result_type</ins>&gt; densities() const;
</pre></blockquote>
</li>

<li>Change 29.5.9.6.3 <a href="https://wg21.link/rand.dist.samp.plinear">[rand.dist.samp.plinear]</a> p. 2, class template <code>piecewise_linear_distribution</code> synopsis
and the prototype description 29.5.9.6.3 <a href="https://wg21.link/rand.dist.samp.plinear">[rand.dist.samp.plinear]</a> before p. 13 as indicated:
<blockquote><pre>
vector&lt;<del>double</del><ins>result_type</ins>&gt; densities() const;
</pre></blockquote>
</li>
</ol>





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