[computer-go] 19x19 MC improvement

[Hiroshi Yamashita]

My program Aya637_4CPU is top on 19x19 CGOS now.
It is temporary, but I'm so happy!
Please don't run full power MoGo, Crazy Stone and Leela :-)

My main improvement was

1. Do not move dead stones.
 Before doing playout, Aya does string capture search up to 7 plies(ladders
 are extended). And set the probability of dead stones's liberty to 1/10000.
 This changed winning rate 0.17 to 0.33 (both are 200 games, 40000po
 against GnuGo 3.7.10) But in 9x9, this method changed nothing.
 There is no ladder search in playout.

2. Change UCT exploration parameter

  exp_param = sqrt(2.0);
  uct = exp_param * sqrt( log(sum of all children playout) /
                        (number of child playout) );
  uct_value = (child winning rate) + uct;

 I changed exp_param sqrt(2.0) to sqrt(0.1).
 This changed winning rate 0.10(660 games) to 0.22(140 games).
 (10000po, against GnuGo 3.7.10)
 I was surprised such a small parameter change made big difference.

AyaMC's sytle is similar to Crazy Stone.
 - progressive windening.
 - pattern is only 3x3 from 10000 professional player's game.
Uct code is like this, http://www.yss-aya.com/uct_aya_e.cpp
In 10000po of the root initial position, 11 nodes are created,
 and 18 candidates are searched

Regards,
Hiroshi Yamashita