From a286b0083333cd716cc6e749bdf397c4a720195a Mon Sep 17 00:00:00 2001
From: "Paul A. Bristow" <pbristow@hetp.u-net.com>
Date: Sun, 26 Aug 2012 09:43:43 +0000
Subject: [PATCH] delta == 0 treated as special case for mean, variance,
 skewness and kurtosis == central Student's t

[SVN r80233]
---
 .../boost/math/distributions/non_central_t.hpp | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/include/boost/math/distributions/non_central_t.hpp b/include/boost/math/distributions/non_central_t.hpp
index 964225d16..558e55127 100644
--- a/include/boost/math/distributions/non_central_t.hpp
+++ b/include/boost/math/distributions/non_central_t.hpp
@@ -522,8 +522,9 @@ namespace boost
             BOOST_MATH_STD_USING
             if (v > 1 / boost::math::tools::epsilon<T>() )
             {
-              normal_distribution<T, Policy> n(delta, 1);
-              return boost::math::mean(n); 
+              //normal_distribution<T, Policy> n(delta, 1);
+              //return boost::math::mean(n); 
+              return delta;
             }
             else
             {
@@ -539,7 +540,10 @@ namespace boost
             {
                return 1;
             }
-
+            if (delta == 0)
+            {  // == Student's t
+              return v / (v - 2);
+            }
             T result = ((delta * delta + 1) * v) / (v - 2);
             T m = mean(v, delta, pol);
             result -= m * m;
@@ -554,6 +558,10 @@ namespace boost
             {
                return 0;
             }
+            if(delta == 0)
+            { // == Student's t
+              return 0;
+            }
             T mean = boost::math::detail::mean(v, delta, pol);
             T l2 = delta * delta;
             T var = ((l2 + 1) * v) / (v - 2) - mean * mean;
@@ -572,6 +580,10 @@ namespace boost
             {
                return 3;
             }
+            if (delta == 0)
+            { // == Student's t
+              return 3;
+            }
             T mean = boost::math::detail::mean(v, delta, pol);
             T l2 = delta * delta;
             T var = ((l2 + 1) * v) / (v - 2) - mean * mean;