From a4900be8904e6c94395b306c7369617f352cbe00 Mon Sep 17 00:00:00 2001
From: Petr Baudis <pasky@ucw.cz>
Date: Wed, 23 Sep 2009 14:29:07 +0200
Subject: [PATCH] UCB1: Do not hack around pass in descend, instead give it a
 fixed prior of 0/10

---
 uct/policy/ucb1.c     |  5 +++++
 uct/policy/ucb1amaf.c | 11 ++---------
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/uct/policy/ucb1.c b/uct/policy/ucb1.c
index 710a56d..189a7cf 100644
--- a/uct/policy/ucb1.c
+++ b/uct/policy/ucb1.c
@@ -98,6 +98,11 @@ ucb1_prior(struct uct_policy *p, struct tree *tree, struct tree_node *node, stru
 	/* Initialization of UCT values based on prior knowledge */
 	struct ucb1_policy *pp = p->data;
 
+	if (is_pass(node->coord)) {
+		node->prior.playouts += 0;
+		node->prior.wins += 10;
+	}
+
 	/* Q_{even} */
 	/* This may be dubious for normal UCB1 but is essential for
 	 * reading stability of RAVE, it appears. */
diff --git a/uct/policy/ucb1amaf.c b/uct/policy/ucb1amaf.c
index eb4f0e0..f9e6974 100644
--- a/uct/policy/ucb1amaf.c
+++ b/uct/policy/ucb1amaf.c
@@ -270,17 +270,10 @@ ucb1srave_descend(struct uct_policy *p, struct tree *tree, struct tree_node *nod
 		if (b->urg_randomm)
 			urgency *= (float)(fast_random(b->urg_randomm) + 5) / b->urg_randomm;
 
-		if (urgency > best_urgency) {
+		if (urgency > best_urgency)
 			best_urgency = urgency; nbests = 0;
-		}
-		if (urgency >= best_urgency) {
-			/* We want to always choose something else than a pass
-			 * in case of a tie. pass causes degenerative behaviour. */
-			if (nbests == 1 && is_pass(nbest[0]->coord)) {
-				nbests--;
-			}
+		if (urgency >= best_urgency)
 			nbest[nbests++] = ni;
-		}
 	}
 #if 0
 	struct board bb; bb.size = 11;
-- 
2.11.4.GIT