From 636272edbe5d170f25703b6f7d79ee394dd766a3 Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <Steinar H. Gunderson sesse@debian.org>
Date: Sat, 17 Mar 2012 14:02:27 +0100
Subject: [PATCH] Add a prior, to smooth out the mu a bit.

---
 bayeswf.cpp | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/bayeswf.cpp b/bayeswf.cpp
index 8b144da..176d345 100644
--- a/bayeswf.cpp
+++ b/bayeswf.cpp
@@ -10,6 +10,8 @@
 
 using namespace std;
 
+#define PRIOR_MU 1500
+#define PRIOR_SIGMA 100
 #define MAX_PLAYERS 4096
 
 float mu[MAX_PLAYERS];
@@ -67,6 +69,15 @@ void update_mu(float *mu, float *sigma, int player_num, const vector<match> &mat
 	}
 
 	float nom = 0.0f, denom = 0.0f;
+
+	// Prior.
+	{
+		float inv_sigma2 = 1.0f / (PRIOR_SIGMA * PRIOR_SIGMA);
+		nom += PRIOR_MU * inv_sigma2;
+		denom += inv_sigma2;
+	}
+
+	// All matches.
 	for (unsigned i = 0; i < matches.size(); ++i) {
 		float sigma1 = sigma[player_num];
 		float sigma2 = sigma[matches[i].other_player];
-- 
2.39.2