Author: Mridul Muralidharan
Date: 12:01:11 03/23/04
Go up one level in this thread
On March 23, 2004 at 13:40:40, Vasik Rajlich wrote:
>On March 23, 2004 at 12:45:39, Joachim Rang wrote:
>
>>On March 23, 2004 at 12:38:29, martin fierz wrote:
>>
>>>On March 23, 2004 at 12:22:16, Tord Romstad wrote:
>>>
>>>>On March 23, 2004 at 11:31:18, martin fierz wrote:
>>>>
>>>>>On March 23, 2004 at 10:14:05, Tord Romstad wrote:
>>>>>
>>>>>>One of the really embarassing things about Gothmog's eval of this position
>>>>>>is that it doesn't even consider the bishop on g1 to be a bad biship. My
>>>>>>bad bishop eval is based on the number of *blocked* pawns on squares of the
>>>>>>bishop's colour. In the position we discuss, there are only two such pawns
>>>>>>(on e3 and g3). Therefore Gothmog thinks that the g1 bishop isn't really
>>>>>>that bad. It has limited mobility, but it should be easy to relocate it
>>>>>>to a better square.
>>>>>
>>>>>perhaps you should change your definition a bit. the pawn on f2 is virtually
>>>>>blocked too, and the pawn on c4 is rather blocked and with it the one on c3. in
>>>>>any case, the f2-pawn should be recognizable as blocked.
>>>>>to evaluate my bishops, i use a sum of c1*(blocked pawns on that color) +
>>>>>c2*(unblocked pawns on that color). i think that is a better way of doing it.
>>>>>still it's not good, because as said, the g1-bishop would be just fine on a3 or
>>>>>on f4.
>>>>
>>>>Thanks for the suggestions. You are probably right, I should have a look
>>>>at my bad bishop code.
>>>
>>>an interesting idea posted here lately (don't remember by who - sorry) was to
>>>look in the forward direction of the bishop and see whether it hits own pawns.
>>>like this, a bishop on a3/f4 in your position gets no penalty, but a bishop on
>>>g1 does. obviously, this criterion alone is not too useful either, but it may be
>>>an ingredient.
>>>
>>>>>>As so often, Gothmog's eval proves to be the worst of them all.
>>>>>no!!! as i said you asked the wrong question! you didn't even answer the right
>>>>>question yourself, and all others won't answer it either as i know them... the
>>>>>right question is:
>>>>>
>>>>>***************************************************************
>>>>>"please give me your static eval with bishop on g1, c1 and a3".
>>>>>***************************************************************
>>>>>
>>>>>my answer is "-0.49 (g1), -0.51(c1), -0.35(a3)."
>>>>
>>>>... and my answer is "+0.24 (g1), +0.18 (c1), +0.31 (a3)".
>>>>
>>>>>as you can see, my answer is always about the same, and for example ridiculous
>>>>>in that g1 is preferred over c1 (reason: the rook's mobility is smaller for
>>>>>Bc1).
>>>>
>>>>Same thing here, as you can see from my numbers.
>>>>
>>>>>i will bet another beer (you owe me one IIRC)
>>>>
>>>>I do. :-)
>>>>
>>>>>that most of the people who
>>>>>answered your post (and of who you think they are evaluating this better) have
>>>>>similar problems. e.g. the position with the bishop on c1/a3 is roughly equal
>>>>>(well, with the Ba3 you in fact immediately win a pawn, but just philosophically
>>>>>speaking, white has little to fear with a pawn for the exchange and the bishop
>>>>>pair) and all those guys who gave a big negative score for white will still be
>>>>>giving a big negative score for white (because nobody is realizing that the
>>>>>g1-bishop is the big problem, they just think exchange=2 pawns), and gothmog's
>>>>>eval will be the superior one.
>>>>
>>>>Do you think that white has the advantage with the bishop at c1?
>>>
>>>no. i think the position is equal. there is nothing black can do do improve as
>>>far as i can see; i.e. there are 3 things he can try:
>>>-> return the exchange by capturing c4 at some point
>>>-> play d5 at some point
>>>-> play a6-b5 at some point
>>>
>>>i don't believe in the pawn breaks, you remove white's weak pawn on c4, open up
>>>the position for the bishops and still have no clear plan. that leaves the first
>>>possibility, but then it's not too clear either. specially if you already have
>>>the bishop on a3 black must also look out for his own weakness on d6. so i think
>>>black does best doing nothing, and white has no active plan either that i can
>>>see, so it's a draw.
>>>
>>>i thought you were unhappy with your evaluation because you were +0.2 while
>>>others were -1.0, which is of course looking bad for you when you have the
>>>bishop on g1, then the others are much better. but with the bishop on c1, the
>>>correct eval is probably about 0, and then your +0.2 are better than the -1.0 of
>>>the others. that's why i said you should be feeling better now. not about the
>>>position with the bishop on g1 of course, but in general - gothmog seems to be
>>>closer to the truth (according to me) than the others.
>>>
>>Shredder 8 manages both:
>>
>>it gives -0.2 for the bishop on c1 and -1.4 for the bishop on g1. Don't ask me
>>how SMK has solved this.
>>
>>regards Joachim
>>
>>
>>>cheers
>>> martin
>>>
>>>
>>>PS:
>>>>Exchange=1.75 pawns in Gothmog, by the way.
>>>better than 2.0 :-)
>
>True. You can often evaluate badly and correctly. It's also important not to get
>hung up on fixing one position - same as with changing your search to solve some
>testsuite position. Some things are just beyond the scope of what your
>evaluation should be doing.
>
>Re. material values, for what it's worth here is my messy code for scoring
>material. These values are pre-computed, and put into a "material lookup table".
>Rybka would evaluate the material here as roughly equal - due to the bishop
>pair, and # of pawns which congests the rook pair.
>
>Vas
>
>// Responsible for setting the weight (from white point of view) of an imbalance
>specified by
>// an MLT index.
>// Applies the three-pass procedure which is also used to set parameters at the
>leaf node:
>// 1) Score according to piece weights.
>// 2) Score according to material imbalance.
>// 3) Score according to (potential) simplified ending.
>void MLTI::Calc_Weight (int MLT_index, char *out_base, char *out_pawn)
>{
> int wh_n, wh_r, wh_q, wh_b;
> int bl_n, bl_r, bl_q, bl_b;
> Get (MLT_index, wh_n, bl_n, wh_b, bl_b, wh_r, bl_r, wh_q, bl_q);
>
> // stage 1: score each piece according to its special weight (currently not
>used)
>
> // stage 2: score imbalance
>
> // score each piece separately according to generic weights
>
> // Basic values:
> // N: 3.25 pawns B: 3.25 pawns B pair: 0.50 pawns R: 5 pawns Q: 9.75 pawns
> // Pawn density:
> // 1/16 pawn extra for N for each pawn above 5 (or -1/16 for below)
> // 1/8 pawn extra for R for each pawn below 5 (or -1/8 for above)
> // Very small bishop v knight bonuses : (note: no additional bonuses for these
>imbalances, only simple ending)
> // BN v NN with nothing else: 1/8 pawn
> // RB v RN, or RRB v RRN: 1/8 pawn
> // QB v QN: -1/16 pawn
> // Piece vs pawns:
> // The presence of move overall material increases value of a piece
> // In endgame B+p v p, B == 2.5 pawns
> // In endgame N+p v p, N == <2.5 pawns (2.4 pawns)
> // R v minor(s):
> // Very favorable for rook to trade other majors
> // R v one minor: 0.2 pawn penalty when all other majors remain
> // 0.2 pawn bonus when all other majors traded
> // R v two majors: 0.3 pawn penalty when all other majors remain
> // 0.3 pawn bonus when all other majors traded
> // Bishop pair increases slighly in value when fighting against the
> // rook, to 0.6 pawns
> // Q v R+minor:
> // Slightly favorable for queen to trade remaining rook pair
> // 0.1 pawn penalty when other rook pair remains
> // 0.1 pawn bonus when other rook pair is traded
> // Bishop pair value is again bumped up to 0.6 pawns
> // Q vs minors
> // Bishop pair value is again bumped up to 0.6 pawns
>
> // Pawn density bonuses: for each white rook, +128 to base, -2 (ie -2/32 of a
>pawn, for each pawn above 8 total)
> // for each white knight, -64 to base, +1 (ie 1/32 of a pawn, for each
>pawn above 8 total)
>
> int base = 0;
> int pawn = 0;
>
> // Basic piece values & pawn densities
> base += (wh_n * ( 250 - 64 ));
> pawn += (wh_n * ( 1 ));
> base -= (bl_n * ( 250 - 64 ));
> pawn -= (bl_n * ( 1 ));
>
> base += (wh_b * ( 250 ));
> base -= (bl_b * ( 250 ));
>
> base += (wh_r * ( 0 + 128 ));
> pawn += (wh_r * ( -2 ));
> base -= (bl_r * ( 0 + 128 ));
> pawn -= (bl_r * ( -2 ));
>
> base += (wh_q * ( 750 ));
> base -= (bl_q * ( 750 ));
>
> // bishop pair bonuses
> if (wh_b >= 2) base += 500;
> if (bl_b >= 2) base -= 500;
>
> // Small bonuses for bishop v knight
> SimpleEnding simple_ending = Get_SimpleEnding ();
> if (simple_ending == KBN_v_KNN) base += 128;
> if (simple_ending == KNN_v_KBN) base -= 128;
> if (simple_ending == KRB_v_KRN) base += 128;
> if (simple_ending == KRN_v_KRB) base -= 128;
> if (simple_ending == KRRB_v_KRRN) base += 128;
> if (simple_ending == KRRN_v_KRRB) base -= 128;
> if (simple_ending == KQB_v_KQN) base -= 64;
> if (simple_ending == KQN_v_KQB) base += 64;
>
> // Piece vs pawns, give bonus to amount of material on the board
> int total_material = Get_MaterialTotal (MLT_index); // -128 to 128
> MaterialImbalance material_imbalance = Get_MaterialImbalance ();
> if ((material_imbalance == B_v_ppp) || (material_imbalance == N_v_ppp))
> base += (total_material * 4); // bonus of up to 512
> if ((material_imbalance == ppp_v_B) || (material_imbalance == ppp_v_N))
> base -= (total_material * 4); // bonus of up to 512
> // in the case of simple minor vs pawns endings, overwrite the previous values
> if (simple_ending == KB_v_K) base = -500; // this is a bit skewed by lines
>which were played to force a draw, an intelligent analysis should be done to get
>the right value
> if (simple_ending == KN_v_K) base = -600;
> if (simple_ending == K_v_KB) base = 500;
> if (simple_ending == K_v_KN) base = 600;
>
> // increase bishop pair bonus by 0.1 pawns when fighting against a rook or
>queen
> if (((wh_r < bl_r) || (wh_q < bl_q)) && (wh_b >= 2) && (bl_b <= 1))
> base += 100;
> if (((wh_r > bl_r) || (wh_q > bl_q)) && (wh_b <= 1) && (bl_b >= 2))
> base -= 100;
>
> int major_pairs = __min (wh_r, bl_r) + __min (wh_q, bl_q);
>
> // bonus of 0.2 pawns to rook vs one minor piece for trading other major pieces
> if ((material_imbalance == R_v_Npp) || (material_imbalance == R_v_Bpp))
> base -= ((major_pairs - 1) * 200);
> if ((material_imbalance == Npp_v_R) || (material_imbalance == Bpp_v_R))
> base += ((major_pairs - 1) * 200);
>
> // bonus of 0.3 pawns to rook vs two minor pieces for trading other major
>pieces
> if ((material_imbalance == Rp_v_BB) || (material_imbalance == Rp_v_BN) ||
>(material_imbalance == Rp_v_NN))
> base -= ((major_pairs - 1) * 300);
> if ((material_imbalance == BB_v_Rp) || (material_imbalance == BN_v_Rp) ||
>(material_imbalance == NN_v_Rp))
> base += ((major_pairs - 1) * 300);
>
> // bonus of 0.1 pawns for queen fighting against rook and minor for trading
>remaining rook pair (0.1 pawn penalty for now doing so)
> if ((material_imbalance == Q_v_RBpp) || (material_imbalance == Q_v_RNpp))
> base -= ((major_pairs * 200) - 100);
> if ((material_imbalance == RBpp_v_Q) || (material_imbalance == RNpp_v_Q))
> base += ((major_pairs * 200) - 100);
>
> // stage 3: according to simplified endings (currently not used)
>
> // convert to units of 32 rather than 1000
> base = (base * 32) / 1000;
>
> *out_base = char (base);
> *out_pawn = char (pawn);
>}
I have very similar code and the idea for which I got from :
http://mywebpages.comcast.net/danheisman/Articles/evaluation_of_material_imbalance.htm
But till now , I have not added all the required imbalances yet ....
Interesting how all masters think alike :)
Mridul
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