Author: Daniel Shawul
Date: 02:22:41 05/13/04
Go up one level in this thread
On May 13, 2004 at 05:13:10, José Carlos wrote: >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... I do all of the things you said above but there is no return (alpha) or return (beta) in my search. The search somehow converges to beta. What i store in hashtables is score. Infact i tried turning off hashtable, null move , and pruning techniques but it all comes back to beta. > > 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) >} That is exactly what i do in my search. > > José C.
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