Author: Eelco de Groot
Date: 06:00:31 08/03/99
Go up one level in this thread
On August 02, 1999 at 20:21:10, Robert Hyatt wrote: >On August 02, 1999 at 12:39:33, J. Wesley Cleveland wrote: > >>On August 02, 1999 at 09:19:29, Robert Hyatt wrote: >> >>>On August 02, 1999 at 06:25:19, José Carlos wrote: >>> >>>> Maybe discarding "bad enought moves" (considering a fixed minimum difference >>>>beteewn first and second move), or the mate-test mentioned could help much in >>>>quick games. >>>> It could be interesting using such idea in games faster than 5min/game. >>>> >>>> José C. >>> >>> >>>There are two obvious problems with this: (1) discarding 'really bad' moves >>>doesn't help... because most use a time-limit for their search. And discarding >>>a few moves at the root doesn't help other than we might barely get one ply >>>deeper than normal; (2) Rememeber that in the position I posted, Bxh6 looks >>>"really bad" at ply 1, 2, etc.. because Qxb6 wins a piece, Bxh6 loses a piece. >>>A difference of 6, roughly... So discarding this move because it looks bad >>>would be a big mistake... >> >>My idea about "forced moves", is to set the search time to 1/3 (more or less) >>the normal, window to (very bad, -infinity), search all moves except the forced >>one, if any moves returns a score better than "very bad", start over with a >>normal search, or else make the forced move without searching it. The idea being >>if all other moves lose, make the one that looks good, and if it is bad, you >>haven't lost much. > > >This is exactly the sort of approach that killed me in 1981. Because all of >the other moves look bad when compared to the 'best' move. Because the best >move wins a piece instantly. None of the other moves appear to do so. And >they _never_ do so. But if you search this 'best' move long enough you realize >it loses, and then the other moves are better... Hello Mr Hyatt! Sorry if I am completely missing the point here, Robert? I never tried any chess-programming myself, so this is just somewhat of a bystanders view: In the above approach, don't you spend most of the search on the bad-looking moves? Because you make a move *instantly* if the other moves prove bad? Why can't you make a case for the opposite view, to spend more time on the promising move, "deepening" it, just to check if it is really that good? That principle wouldn't suddenly not apply if it is an "easy" move. The sooner you find out the earlier you can switch to another move or decide to make the move on the board. I always thought that the main point of doing all the iterations on the different plydepths is to (a) try to steer the most promising rootmove to the top of the rootmove list and (b) because you can never be sure that the most promising move is actually the best move, to order the rest of the rootmoves as best as you can so that you know where to look for a new candidate. Because any profit you make with alpha-beta is at the expense of (b) it would seem to make some sense to do "less" alpha-beta if you really can't be to sure of your principal move. And that is the case in the first iterations so why not try to do less alpha-beta cutoffs there somehow. The fact that there seems to be an "easy" move just means that there is a somewhat higher probability that you can achieve (a). So why not spend some of the expected profit of lots of alpha-beta cutoffs at deeper iterations on (b)? The search speed goes down enormously but you can afford it at shallow plydepths. And at greater plydepths the chances are that there have been some changes at the top of the the movelist so that means that there are likely better variations available then for the second-best move etc. Because at one time they may have been the principal move. And if you spend more time on "deepening" the principal move on shallow plydepths by whatever means, more quiescense search or whatever, these variations only get better. The move ordering gets better this way. And I don't really see why all this applies only at the root. If deeper in the tree you see a promising move you can expect more alpha-beta cut offs. So go a little deeper on this promising move and if it holds try to do some more move ordering at that branch. Then continue with the standard alpha-beta for the second move at that branch. But first you have to check the most promising move. Could you please shoot some holes in this? Thanks! Eelco.
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