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Daniel Shawul
Joined: 14 Mar 2006
Posts: 2185
Location: Ethiopia
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 Post subject: Re: Plunder raids and pruning bad captures Posted: Fri Jun 29, 2012 11:54 am |
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| hgm wrote: |
| Daniel Shawul wrote: |
| Do you mean a counter-attack is rarely fatal ? |
No, I meant what I said, that it is usually fatal. Proper response to a threat is to solve it, not create an equivalent counter attack.
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For example, white attacks q with his B, and black then replies (counter-attacks) Q with his b.Then in qsearch white has now two options: Bxq or Qxb. Thus Bxq can never loose and will be tried first but Qxb will be an equal exchange after bxQ. So black can make a counter attack or not outside the qsearch but he needs to make sure he will get equal exchange when he does a counter attack.I understand your argument that Qxb may be better than Bxq because in the latter case I know the opponent will capture my Q if I have a hanging pieces evaluator. The only advantage of Qxb would be white will have the upper hand if the raid continues with both queens attacking unprotected pieces. So that is the only
downside I see with black making the counter attack.
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| I think many do not search any kind of attacking moves in QS for fear of explosions. I can see this happening in standard chess even if we consider threats to Queen (MVP). |
In QS you would of course not search attacks through non-captures. But the point is that there can be captures that at the same time create new attacks. Especially Queen-class pieces are very adept at eating themselves through the opponent's lines; once it has breached the outer defense, it usually has a choice out of multiple captures, and each of these captures opens new attacks on several more targets.
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| The qsearch will consider capturing the opponent queen first. You can also try to identify this situation as perfectly as possible and apply the Queen capture that SEE tosses out. The search will stop early even if the move was a mistake since it would be a total blunder. |
Well, perhaps it would be sufficient to exempt captures with a hanging piece from SEEing, even if they are HxL.(For LxH and equal captures I already skip SEE.), and that they should actually not be ranked according to the victim in the MVV ordering, but according to the value of the mover. E.g. if I have Qx(unprotected)R and Rx(protected)B, while the latter R was hanging (i.e. attacked and not protected), standard ordering would be to start with QxR, (which then is refuted by my hanging Rook being captured), and not consider the RxB at all (because SEE tells us it loses the exchange). But when saving your own hanging pieces gets priority over capturing equivalent hanging pieces of the opponent, and are tried unSEEn, the RxB would be tried first (and probably gain you a minor, because you play QxR when he recaptures the Rook, or withdraw your Rook when he saves his).
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I agree. It should be safe to try out such moves since it happens in rare occasions. From experience we know MVV/LVA without SEE works well. So trying out a few more captures "out of order" in the special case where we have a hanging pieces should not increase the tree size much. Infact I do not use SEE in Nebiyu since it is difficult to adapt it to general games. So in effect I try all captures (loosing or not) and use futility pruning one ply later to remove many of them from being searched further.If you have the hanging piece info in your eval you can reorder the moves as much as you want to achieve the desired result. I say use MVV and avoid the headache with the Lion piece.
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I also wonder whether captures of victims lower than your own highest hanging piece should not be considered bad captures, even if their SEE is good. E.g. if I have a hanging Rook, PxB is not so hot, because he will of course not recapture the P, but retaliate against my Rook, so that I in fact lose an exchange in the first two ply. So captures of anything worth less than a Rook are in general not advisable when I have a hanging Rook.
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I have tried this in the past when I had a hanging pieces evaluation code through Ed's attack sets. It is like doing futility pruning one ply earlier. That pruning tries only captures that bring up our score to equal levels or more. So you can achieve the same effect one ply earlier by not trying captures that don't gain more than our hanging pieces.
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Hanging pieces will be much more common in Chu Shogi, because basically every piece suffering a contact attack from a Lion should be considered hanging, no matter how well it is protected. Because the Lion can withdraw from the square after capture, with the second leg of its move.
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Two leg movers will definately require a re-think of SEE. It is not an exchange on the same square anymore if the lion will move away from the hot spot in the second leg.
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Perhaps capturing with check by hanging pieces should also get priority over capturing valuable victims. |
Yes but you can only try such schemes if SEE don't prune it already. So stick with MVV/LVA if it doesn't explode chu-shogi qsearch. Even if it does start from there, and then re-order or remove those captures that you will not want to try gradually.
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Plunder raids and pruning bad captures