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New idea for "easy move detection"
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Rasmus Althoff



Joined: 30 Aug 2016
Posts: 773

PostPost subject: New idea for "easy move detection"    Posted: Sat Nov 05, 2016 10:39 pm Reply to topic Reply with quote

I've implemented an "easy move detection" to the CT800.

The algorithm goes as follows:

- In the root position, do the normal alpha-beta-minimax move sorting at depth 3 plus QS.
- Check whether the drop from the best to the second best move is at least 240 centipawns (cps).

- If none of the following conditions a) and b) holds true, reduce the score drop to 0 (preventing the "easy move" shortcut):
a) the opponent's move was in the PV, and the "easy move" was calculated as answer.
b) the position evaluation for the "easy move" from the move sorting above is within a window of +/- 50cps from the previous move turn. I maintain a "last valid eval" variable anyway for lazy middlegame static evaluation.

If the score drop is still above 240, then perform a regular NegaScout search including check extensions and QS until depth 4. If the "easy move" is still at the top of the PV, stop the calculation.

The ideas here:

- the "easy move" could as well be a trap. While the opponent might just hang a piece, it is also possible that there is something to it. So if the move fails on the high side of the +/- 50cps window, then don't take the bait. As always in life - when something is too good to be true, then probably it isn't.

- the "easy move" might in fact be bad because the CT800 has already detected e.g. a deeper mate in the previous search (fails on the low side of the +/- 50cps window). That is especially important if the mating combination has already cost some material.

Note: the situations when there is only one legal move or only one move that avoids being mated in the next move are handled separately from this logic.
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Subject Author Date/Time
New idea for "easy move detection" Rasmus Althoff Sat Nov 05, 2016 10:39 pm
      Re: New idea for "easy move detection" Michael Sherwin Sat Dec 24, 2016 4:14 am
            Re: New idea for "easy move detection" Rasmus Althoff Sat Dec 24, 2016 10:35 am
      Re: New idea for "easy move detection" H.G.Muller Sat Dec 24, 2016 8:59 am
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