<p>In <a href="https://github.com/mlpack/mlpack/pull/729#discussion_r71538410">src/mlpack/core/dists/gamma_distribution.cpp</a>:</p>
<pre style='color:#555'>&gt; @@ -0,0 +1,76 @@
&gt; +/**
&gt; + * @file gamma_distribution.cpp
&gt; + * @author Yannis Mentekidis
&gt; + *
&gt; + * Implementation of the methods of GammaDistribution.
&gt; + */
&gt; +#include &quot;gamma_distribution.hpp&quot;
&gt; +
&gt; +#include &lt;boost/math/special_functions/digamma.hpp&gt;
&gt; +#include &lt;boost/math/special_functions/trigamma.hpp&gt;
</pre>
<p>I replaced trigamma(.) with polygamma(2, .) to see if that works. According to <a href="http://mathworld.wolfram.com/PolygammaFunction.html">this</a>, I could avoid including it completely and compute it using digamma. I'm trying that while travis attempts to build the new version.</p>

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