[mlpack-git] master: Replaces trigamma(a) with polygamma(1, a) to check compatibility (32fee02)

[gitdub at mlpack.org]

Repository : https://github.com/mlpack/mlpack
On branch  : master
Link       : https://github.com/mlpack/mlpack/compare/ba850f782a53c5a77b7985f7647f609bd96cb5e7...2c026d838925df436d967439899813da5d34c702

>---------------------------------------------------------------

commit 32fee02c8e43725f072cd0ec293005a1a09034cf
Author: Yannis Mentekidis <mentekid at gmail.com>
Date:   Wed Jul 20 15:40:03 2016 +0100

    Replaces trigamma(a) with polygamma(1, a) to check compatibility


>---------------------------------------------------------------

32fee02c8e43725f072cd0ec293005a1a09034cf
 src/mlpack/core/dists/gamma_distribution.cpp | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/mlpack/core/dists/gamma_distribution.cpp b/src/mlpack/core/dists/gamma_distribution.cpp
index bb52ce6..922212c 100644
--- a/src/mlpack/core/dists/gamma_distribution.cpp
+++ b/src/mlpack/core/dists/gamma_distribution.cpp
@@ -7,7 +7,7 @@
 #include "gamma_distribution.hpp"
 
 #include <boost/math/special_functions/digamma.hpp>
-#include <boost/math/special_functions/trigamma.hpp>
+#include <boost/math/special_functions/polygamma.hpp>
 
 using namespace mlpack;
 using namespace mlpack::distribution;
@@ -31,7 +31,8 @@ void GammaDistribution::Train(const arma::mat& rdata)
 
   // Use boost's definitions of digamma and tgamma, and std::log.
   using boost::math::digamma;
-  using boost::math::trigamma;
+  //using boost::math::trigamma;
+  using boost::math::polygamma;
   using std::log;
 
   // Allocate space for alphas and betas (Assume independent rows).
@@ -59,7 +60,8 @@ void GammaDistribution::Train(const arma::mat& rdata)
 
       // Calculate new value for alpha. 
       double nominator = meanLogx - logMeanx + log(aEst) - digamma(aEst);
-      double denominator = pow(aEst, 2) * (1 / aEst - trigamma(aEst));
+      //double denominator = pow(aEst, 2) * (1 / aEst - trigamma(aEst));
+      double denominator = pow(aEst, 2) * (1 / aEst - polygamma(1, aEst));
       assert (denominator != 0); // Protect against division by 0.
       aEst = 1.0 / ((1.0 / aEst) + nominator / denominator);