Author: José Carlos
Date: 02:13:10 05/13/04
Go up one level in this thread
On May 13, 2004 at 04:56:23, Daniel Shawul wrote: >On May 13, 2004 at 04:20:02, José Carlos wrote: > >>On May 13, 2004 at 03:35:00, Daniel Shawul wrote: >> >>>Hello >>> >>>My search is fail soft(i return the actual score) >>>when i fail high at the root i widen the window by 3 pawns (300). >>> >>> if(score<=r_alpha) >>> { >>> r_beta=r_alpha; >>> r_alpha=score-300; //r_alpha = -MATESCORE; >>> } >>> else if(score>=r_beta) >>> { >>> r_alpha=r_beta; >>> r_beta=score + 300; //r_beta = MATESCORE; >>> } >>>If the search fail's high at 1.75 score but the real score was 10 >>>i get a score of 4.75 (1.75 + 3) in the next iteration. Why? my search is fail >>>soft and the score returned should be independent of beta. If i change the 200 >>>to 300,score returned is 4.75?? > > a correction (1.75 + 2) = 3.75 > >> >> Are you sure you're doing fail soft? I mean, you need some extra logic, like >>starting off with -INFINITE in alpha nodes and increase the best score even in >>fail lows. You also need to make sure of returning true bounds in qsearch. Also, >>if you do some kind of forward prunning depeding on alpha and beta you won't be >>able to return true scores. > > i do futility pruning and other purnings but i always return > (score + margin) in all of the cases. Not alpha. > >for example in the following test position > rnb2rk1/ppq2p1p/4p1p1/3pP1B1/3P1Q2/2b2N2/P1P2PPP/2RK1B1R w - - 8 14 > > 1& 34 -0.31 0.05 1. Qxf7+? > 1 36 -0.10 0.05 1. Bd3 > 2 138 -0.44 0.09 1. Bb5 > 2 172 -0.24 0.09 1. Bf6 > 3 447 0.10 0.14 1. Bf6 Qa5 > 3 679 0.16 0.16 1. Bh6! > 3 781 0.18 0.16 1. Bh6 Rd8 > 4 1899 0.15 0.20 1. Bh6 Rd8 2. Qf6 Nc6 > 5 3778 0.47 0.27 1. Bh6 Re8 2. Qf6 > 6 10330 0.71 0.33 1. Bh6 Rd8 2. Qf6 > 7 26798 1.06 0.44 1. Bh6! > 7 86808 1.48 0.63 1. Bh6 Qe7 2. Bxf8 Qxf8 3. Qf6 Nd7 > 8 208184 1.20 0.95 1. Bh6 Qe7 2. Bxf8 Qxf8 3. Bd3 Nd7 > 4. Ng5 Qg7 > 9 684592 1.40 2.27 1. Bh6 Nd7 2. Ng5 a6 3. f3 >10 3253930 1.42 9.00 1. Bh6 Qe7 2. Qe3 Qb4 3. Bxf8 Kxf8 > 4. Qh6+ Kg8 5. Bd3 f6 >10 5270072 1.75 15.05 1. Bf6! >10 11120355 3.75 33.33 1. Bf6! //here score is 1.75+2=3.75 > //full window opened >10 32259429 12.82 87.59 1. Bf6 Qxe5 2. Nxe5 Nd7 3. Nxd7 Bd2 > 4. Kxd2 Bxd7 5. c4 >11& 32784106 12.47 89.17 1. Bf6? Qxe5 > > if i change margin to 3,the result will be something like this >10 11120355 4.75 33.33 1. Bf6! >10 32259429 12.82 87.59 1. Bf6 Qxe5 2. Nxe5 Nd7 3. Nxd7 Bd2 > 4. Kxd2 Bxd7 5. c4 >11& 32784106 12.47 89.17 1. Bf6? Qxe5 > > I am very very sure i don't return alpha/beta anywhere in my search. >I also tried turning off hashtable ,nullmove,iid etc but no success. > >best >daniel I don't find the effect you present here any strange. I can be caused by many things: - Null move: you can cutoff with a much lower score than true score cause you allow the opponent two moves in a row. - Hashing: cutting off by a stored bound from a different depth - Move ordering: if you search moves a, b and c with scores +1, +2, +10 you'll cutoff with beta <= +1 in the first move, with beta <= +2 in the second. - Forward pruning: if score > beta + margin and (some conditions) return(beta + margin) or return(beta)-not true score-. - Lazy cutoffs Etc... If all of that is disabled, then make sure you have something like (simplified search, and also in qsearch): search(alpha,beta,depth) { int best = -INFINITY; // Make sure you start with -INF, not with alpha int score; while(all moves) { score = -search(); if (score >= beta) return(score); if (score >= best) best = score; // update this even when score <= alpha } return(best) } José C.
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