Author: Vasik Rajlich
Date: 10:40:40 03/23/04
Go up one level in this thread
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);
}
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