From cd0f0392bdcfafd1b9dcce4de08ffdd9a1a36ce1 Mon Sep 17 00:00:00 2001
From: Alexey Khudyakov <alexey.skladnoy@gmail.com>
Date: Sun, 22 Jan 2012 17:03:01 +0400
Subject: [PATCH] Fix bug in incompleteGamma

Approximation for case s>1000 was calculated wrongly.
---
 Numeric/SpecFunctions.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Numeric/SpecFunctions.hs b/Numeric/SpecFunctions.hs
index d4cfd23..8b2a148 100644
--- a/Numeric/SpecFunctions.hs
+++ b/Numeric/SpecFunctions.hs
@@ -178,7 +178,7 @@ incompleteGamma p x
     | otherwise       = let g = p * log x - x - logGamma p + log cf
                         in if g > limit then 1 - exp g else 1
   where
-    norm a = erfc (- a / m_sqrt_2)
+    norm a = 0.5 * erfc (- a / m_sqrt_2)
     pearson !a !c !g
         | c' <= tolerance = g'
         | otherwise       = pearson a' c' g'