I was recently working on a UCT bot for Arimaa by trying to generate a random move directly, instead of generating all moves and selecting a random one. This general method sped up the random playout rate by a factor of 5, which seemed wonderful.
Unfortunately, the new faster random bot consistently lost to the older, slower bot that was getting 5x fewer playouts. After some experimentation, I found that the problem was a bias built into my random move generator. At one point in the process, a random piece has been selected and it can move in any direction. The "bad" code selected a random direction, then proceeded clockwise in the other directions if that one wasn't legal. The "good" code selects a random direction among the directions not tried yet. It's pretty shocking to me that the "bad" code still had an unacceptable bias; in fact one so severe that it always played worse, and sometimes made the obviously worst possible move. _______________________________________________ Computer-go mailing list Computer-go@dvandva.org http://dvandva.org/cgi-bin/mailman/listinfo/computer-go
