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Re: [gnugo-devel] thrashing dragons again


From: Arend Bayer
Subject: Re: [gnugo-devel] thrashing dragons again
Date: Wed, 5 Jan 2005 01:01:42 +0100 (CET)

I wrote:
> Gunnar wrote:
> 
> > Arend wrote:
> > > - We use the thrashing dragon heuristic much more often: Do it even if we
> > > are behind (up to 30 pts), and don't bother to make it dependant on the
> > 
(...)
> > I'm not sure I agree with this. Consider the case where the game is
> > pretty much over and GNU Go is about to lose by half a point. Then the
> > opponent (stupid computer or confused human) inexplicably adds a stone
> > to a dead dragon without a working followup. I would be very annoyed
> > if GNU Go answered with a restraining move inside own territory, not
> > taking the gift.

> For the record: If I change 30.0 to 0.0, there are 3 PASSes that go away:
> nngs:440, gunnar:46, 9x9:250. I will try to think about this more.

This was nngs2:440.

Looking at these again:
9x9:250 is a lost game, so it doesn't matter much what GNU Go plays. 

nngs2:440 is a game where GNU Go is behind, it is not clear whether the
thrashing dragon can live (to me at least). It may actually be worth
gambling with a tenuki.

gunnar:46 is a game that is close, where the correct move (O11)
clearly better than O9 (played without my patch), so that the thrashing
dragon logic (against N13) seems to work well.

So we have only one useful PASS; I think this is not enough to counter
Gunnar's objections, and so I plan to revert this as below.

Arend



Index: engine/genmove.c
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/genmove.c,v
retrieving revision 1.102
diff -u -p -r1.102 genmove.c
--- engine/genmove.c    24 Dec 2004 20:13:47 -0000      1.102
+++ engine/genmove.c    5 Jan 2005 00:00:45 -0000
@@ -421,14 +421,13 @@ do_genmove(int color, float pure_threat_
   /* Look for moves to break mirror play by the opponent. */
   break_mirror_go(color);
 
-  /* If we are ahead by 10 points or more, consider a thrashing
+  /* If we are ahead by 5 points or more, consider a thrashing
    * dragon dangerous and change its status from DEAD to
-   * UNKNOWN. This may generate a move. Otherwise, pretend there is no
-   * thrashing dragon.
+   * UNKNOWN. Otherwise, pretend there is no thrashing dragon.
    */
   if (!doing_scoring && !limit_search)
     use_thrashing_dragon_heuristics
-      = revise_thrashing_dragon(color, our_score, -30.0);
+      = revise_thrashing_dragon(color, our_score, 5.0);
   
   /* The general pattern database. */
   shapes(color);




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