Dan wrote: > However I admit that the best method of filtering them is a little > unclear due to this type of example. One way would be not to > accept a snapback move unless it is the only owl attack > move for some dragon. Or maybe your method of giving a > negative shape value is simpler and better.
I'm suddenly getting deja-vu feelings. Ah, from this discussion: http://lists.gnu.org/archive/html/gnugo-devel/2004-11/msg00062.html The patch in that message filters out send-two-return-one moves from consideration in do_find_more_owl_attack_and_defense_moves(), which should be equally effective for moves playing into snapback. Indeed, the attached patch changes the original example to Q7: 2.33 (followup) - threatens to capture Q6 Q7: 5.25 (followup) - threatens to capture R8 Q7: not a safe move [...] Top moves: 1. T6 28.90 2. R5 25.80 3. P2 9.24 4. R4 6.93 which is as effective as we could hope for. However, before this patch can be used it's necessary to do some preparations so that playing_into_snapback() isn't sometimes called with the first move already trymoved. See http://trac.gnugo.org/gnugo/ticket/74 for a patch and further explanations. /Gunnar Index: engine/liberty.h =================================================================== RCS file: /cvsroot/gnugo/gnugo/engine/liberty.h,v retrieving revision 1.252 diff -u -r1.252 liberty.h --- engine/liberty.h 25 Jan 2006 17:14:04 -0000 1.252 +++ engine/liberty.h 31 Jan 2006 17:24:01 -0000 @@ -530,6 +530,7 @@ int double_atari(int move, int color, float *value, signed char safe_stones[BOARDMAX]); int send_two_return_one(int move, int color); +int playing_into_snapback(int move, int color); int play_attack_defend_n(int color, int do_attack, int num_moves, ...); int play_attack_defend2_n(int color, int do_attack, int num_moves, ...); int play_break_through_n(int color, int num_moves, ...); Index: engine/utils.c =================================================================== RCS file: /cvsroot/gnugo/gnugo/engine/utils.c,v retrieving revision 1.112 diff -u -r1.112 utils.c --- engine/utils.c 29 Jan 2006 18:36:59 -0000 1.112 +++ engine/utils.c 31 Jan 2006 17:24:01 -0000 @@ -1396,6 +1396,26 @@ } +/* Returns true if a move by (color) plays into a snapback. */ +int +playing_into_snapback(int move, int color) +{ + int libs[2]; + int k; + + if (approxlib(move, color, 1, NULL) != 0 + || accuratelib(move, color, 2, libs) != 1) + return 0; + + for (k = 0; k < 4; k++) + if (board[move + delta[k]] == color + && adjacent_strings(libs[0], move + delta[k])) + return 1; + + return 0; +} + + /* Score the game and determine the winner */ void Index: engine/value_moves.c =================================================================== RCS file: /cvsroot/gnugo/gnugo/engine/value_moves.c,v retrieving revision 1.161 diff -u -r1.161 value_moves.c --- engine/value_moves.c 25 Jan 2006 17:14:04 -0000 1.161 +++ engine/value_moves.c 31 Jan 2006 17:24:03 -0000 @@ -297,6 +297,10 @@ if (send_two_return_one(pos, color)) return; + /* Never consider moves playing into snapback here. */ + if (playing_into_snapback(pos, color)) + return; + save_verbose = verbose; if (verbose > 0) verbose --; _______________________________________________ gnugo-devel mailing list gnugo-devel@gnu.org http://lists.gnu.org/mailman/listinfo/gnugo-devel
