easy move?

[AlvaroBegue]

In Shokidoki I consider a move easy if there is at least a 300cP gap between its score and that of the second-best move, in all iterations.

How do you get the score for second best in ID? Do you always perform multi variant analysis? I think the second best (and all others) will just fail low after alpha has been established by the first move.

What about looking up all the other moves (besides the best move) in the transposition table?

No, that won't help. What Ras is pointing out is by the nature of alpha-beta search (and even more so NegaScout or PVS), the only thing we learn about other moves is that their scores are not better than the score of the best move, but we don't know by how much. Of course one could do additional null-window searches to establish the 50cp difference. At depth 6 this isn't very costly at all.

My old program Ruy-López had an easy-move heuristic, where I established the difference in score was large at depth 1, and then I would remove the easy-move flag if another move became best at any time. The effect of the flag was allowing only a small fraction of the usual time per move to be spent (1/20th, I believe). In some versions I think I also required that some large fraction of the search time was being used in the first move (meaning that it's easy to prove the other moves are inferior).

However, in my newer program RuyDos I don't do this. That's because Ruy-López would clear the hash tables between moves, and then the checks I described above make sense. In RuyDos the hash table is not cleared between moves, which means I don't gain any information about how consistent the results of the searches at different depths are, because all the low depth searches get short-circuited by hash-table data.

[D Sceviour]

Rather than looking for easy moves to reduce time, instead try adding more time for difficult positions. For each root PV change per iteration, add an incremental time step.

[Robert Pope]

I guess one of the reasons people think that easy move is not worth it is that they only test in ponder-off games. Spending a lot of time on an easy move in a ponder-on game is giving the opponent free thinking time on a guaranteed ponder hit. Of course some variants have more easy moves than others.

In Shokidoki I consider a move easy if there is at least a 300cP gap between its score and that of the second-best move, in all iterations.

I think it's more a concern that the effort to save time/shorten opponents ponder-time will end up being at the cost of a blunder.

[Ras]

I think it's more a concern that the effort to save time/shorten opponents ponder-time will end up being at the cost of a blunder.

This is especially likely when the situation is just to good to be true. That's why I check back whether the result of the move is within the overall range from the last move turn. If it's just like +300 centipawns out of nowhere, this looks suspicious and is worth regular investigation. It's not trivial to have that check for a UCI engine, but it's still possible to verify whether the current position is a continuous game.

If it isn't a continuation so that there is no valid last move turn score, then better drop any "easy move" approach except if it's the only legal move.

[hgm]

I think it's more a concern that the effort to save time/shorten opponents ponder-time will end up being at the cost of a blunder.

You can say exactly the same thing for any reduction in the search. Yet we know that reductions pay off, and that a fixed-depth search is crap. Because compared to a search with reductions, the fixed-depth search with the same number of nodes effectively reduces the important branches rather than the crappy ones.

If you can recapture a Queen in only one way after QxQ, it would be extremely foolhardy to keep thinking and thinking after at d=1 you already found NxQ as best move, just on the off chance that in this case it might be better not to recapture that Queen, and play on with a Queen down.

Point is that you always have limited resources, and that allocating more resources to any particular sub-problem, although always better for that sub-problem, will always go at the expense of deteriorating the situation in other sub-problem. When you would consider the shortened thinking time in case of an easy move the norm, so that you have a large supply of 'spare' time to allocate to improve on your play compared to that faster TC, that extra time would be best spent thinking about positions where there is a high chance to actually change the move choice for the better. Positions where you are a Queen down will hardly ever turn into positions where you are ahead. And if the only move that keeps you about equal at low depth turns out to lose more than a Queen at high depth, your only hope is that the opponent will not see it, as he will certainly preserve the advantage of a Queen when you do not recapture, even in the 1-ply iteration. Giving him extra (ponder) time in that situation is really the worst thing you could do.

[odomobo]

There's also more discussion on this topic in this thread: http://talkchess.com/forum3/viewtopic.php?f=7&t=67944