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End-game evaluation
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H.G.Muller



Joined: 10 Mar 2006
Posts: 12765
Location: Amsterdam
PostPost subject: Re: End-game evaluation    Posted: Wed Oct 19, 2011 4:54 pm Reply to topic Reply with quote
Desperado wrote:
You can also scale the complete evaluation (not only the material value), and store a flag in your material table when you like to do so.

That is what I do now. (And what Fruit does.)

Quote:
If you think of opposite bishops for example, even with 2 connected passers ahead
it often will be draw (if they can be easily blocked for example).

This is also already in: I consider the two Bishops different piece types in the material index (so there are 4 Bishop states per side, rather than 3), so that I can put in different scaling flags for like and unlike Bishops. Fruit does not make this distinction in its material key, but it sets a flag for B vs B (+ suitable numbers of pawns) in the table contents to trigger explicit testing of the B colors in the evaluation.

Quote:
* How do you handle the exchange ? especially if you classify
"being ahead" (i am thinking of constellations like: KRPP - KBNPP).
My feeling and my observations are, that the side with the rook
has the better play in many cases. Question


Conventional piece-value wisdom has it that the side with the two minors is ahead here. But with two Pawns, Fruit considers neither of those as drawish. At least not as more drawish than the regular additive eval score would suggest. Apart from unlike B with an imbalance of upto 2 Pawns, (but an arbitrary number of them), Fruit only discounts combinations with 0 or 1 Pawn.

In my simplified system I now discount (apart from the unlike Bishops case) with the following imbalances (meaning there can be more material than the mentioned if it is balanced, and neither side has two majors):

Code:
1) one light piece ahead
  a) without Pawns and none of my light pieces has mating potential by itself (otherwise I would trade until that piece is left)
  b) with one Pawn and just two Knights (as he can sac my Pawn away with his minor)
2) exchange ahead
  a) only without Pawns (he cannot afford to sac anything for a Pawn)
3) equal light pieces
  a) without Pawns
  b) with one Pawn if none of my light pieces has mating potential by itself (he can sac a piece for my Pawn to get into (1a))
  c) with two Pawns if I have just a pair of Knights (he can afford to sac both minors for my Pawns).
4) exchange behind
  a) without Pawns (but I cannot be ahead in that case?)
  b) with one Pawn *
5) one light piece behind
  a) without Pawns (but again, we cannot be ahead here?)
  b) with one Pawn (he can sac one of his pieces, to convert to (3a)
  c) with two Pawns, when none of my light pieces has mating potential by itself (a piece-for-paw sac converts to (3b))
6) Rook vs two light pieces
  a) without Pawns
  b) with one Pawn (piece-for-pawn sac converts to (2a))
7) two light pieces vs Rook
  a) without Pawn, unless two of my light pieces have mating potential by themselves. (A Rook sac on a single piece with mating potential gives (1a))
  b) with one Pawn and two Knights (Rook sac for the Pawn destroys my mating potential)


The case marked by * has some exceptions. If there are other light pieces, he can sac one of them for the Pawn, to get to (7a). (The exception there is for Spartan Chess, and should thus also be made in (4b).) If there are no other pieces, he might have to sac the Rook for the Pawn, which he can still afford if my light piece has no mating potential.

KBBKN (and KBBKNP?) should be an exception to case (1). In my current system I can only make that exception by not discounting it at all, because the default multiplier for Pawnless material is 1/8. Fruit gives it 1/2 (which seems deserved by the fact that most wins would exceed the 50-move rule). So I might extend my system with some special codes to discount both sides by 1/2 irrespective of their number of Pawns.

I am not sure how to treat overwhelmingly won end-games that contain fortress draws. I guess they should still be discounted by default. Because when you are in a fortress, the search would stay their irrespective of search depth, while a lost position would at some depth find the winning conversion, and the score would be corrected accordingly. In end-games like KQKBN most won positions would be won at reasonably low depth. Perhaps these would also be good candidates for the unconditional 1/2 reduction.
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Subject Author Date/Time
End-game evaluation H.G.Muller Tue Oct 04, 2011 11:44 am
      Re: End-game evaluation Evert Glebbeek Tue Oct 04, 2011 1:02 pm
            Re: End-game evaluation H.G.Muller Tue Oct 04, 2011 2:20 pm
      Re: End-game evaluation Oliver Uwira Tue Oct 04, 2011 1:59 pm
      Re: End-game evaluation Jon Dart Tue Oct 04, 2011 2:10 pm
            Re: End-game evaluation Jon Dart Tue Oct 04, 2011 2:13 pm
      Re: End-game evaluation Kevin Hearn Tue Oct 04, 2011 8:19 pm
            Re: End-game evaluation Pawel Koziol Wed Oct 05, 2011 10:46 am
      Re: End-game evaluation H.G.Muller Mon Oct 10, 2011 8:09 am
            Re: End-game evaluation H.G.Muller Mon Oct 10, 2011 9:00 am
                  Re: End-game evaluation Evert Glebbeek Mon Oct 10, 2011 1:04 pm
                  Re: End-game evaluation Ed Schroder Mon Nov 07, 2011 10:15 pm
            Re: End-game evaluation H.G.Muller Wed Oct 19, 2011 10:16 am
                  Re: End-game evaluation Michael Hoffmann Wed Oct 19, 2011 11:48 am
                        Re: End-game evaluation H.G.Muller Wed Oct 19, 2011 1:24 pm
                              Re: End-game evaluation Michael Hoffmann Wed Oct 19, 2011 2:53 pm
                                    Re: End-game evaluation Volker Annuss Wed Oct 19, 2011 4:53 pm
                                    Re: End-game evaluation H.G.Muller Wed Oct 19, 2011 4:54 pm
                                          Re: End-game evaluation H.G.Muller Sat Oct 22, 2011 5:29 pm
                                                Re: End-game evaluation H.G.Muller Mon Nov 07, 2011 7:28 pm
                                                      Re: End-game evaluation Evert Glebbeek Mon Nov 07, 2011 8:33 pm
                                                            Re: End-game evaluation Evert Glebbeek Mon Nov 07, 2011 9:02 pm
                                                                  Re: End-game evaluation H.G.Muller Mon Nov 07, 2011 9:40 pm
                                                            Re: End-game evaluation H.G.Muller Tue Nov 08, 2011 11:16 am
                                                                  Re: End-game evaluation Evert Glebbeek Tue Nov 08, 2011 5:50 pm
                                                                        Re: End-game evaluation H.G.Muller Tue Nov 08, 2011 8:16 pm
                                                                              Re: End-game evaluation Evert Glebbeek Tue Nov 08, 2011 8:52 pm
                                                                                    Re: End-game evaluation H.G.Muller Tue Nov 08, 2011 10:14 pm
                                                      Re: End-game evaluation Karlo Bala Jr. Mon Nov 07, 2011 11:59 pm
                                                            Re: End-game evaluation H.G.Muller Tue Nov 08, 2011 7:30 am
                                                                  Re: End-game evaluation Kevin Hearn Tue Nov 08, 2011 9:58 am
                                                                        Re: End-game evaluation H.G.Muller Tue Nov 08, 2011 12:40 pm
                                                                              Re: End-game evaluation Evert Glebbeek Tue Nov 08, 2011 5:53 pm
      Re: End-game evaluation Mark Lefler Mon Oct 10, 2011 4:08 pm
            Re: End-game evaluation H.G.Muller Mon Oct 10, 2011 9:09 pm
                  Re: End-game evaluation H.G.Muller Mon Oct 10, 2011 9:58 pm
                  Re: End-game evaluation H.G.Muller Tue Oct 11, 2011 8:50 am
                        Re: End-game evaluation H.G.Muller Tue Oct 18, 2011 6:36 pm
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