rbarreira wrote:diep wrote:
Also all this selective searching can of course only work using my lemma of 90s, which was disputed at the time, that is that there is a tactical barrier above which only positional searching deeper is interesting.
What is this tactical barrier? Are you saying that beyond a certain search depth, the search will stop picking up "tactics"? So you're saying that the positions deep in the search tree don't have deep tactics waiting to be found any more?
That sounds strange and IMHO unlikely...
The religion in the 90s, though not shared by all chess programmers,
a good example there is Don Dailey, was that every additional ply lineair scaled further tactical.
So a program searching 6 ply would always beat a 5 ply program,
just like a 17 ply program would beat with the exact same percentage
a 16 ply program.
Realize how difficult it was back then to test, so all sorts of lemma's that look silly nowadays, they were used by even some strong top programmers.
They said the next thing simply: "each year we won X elopoints".
Every ply would be 70 elopoints for example.
Now in 1997 we got like 10 ply or so. Some a bit more some a bit less.
So todays 30+ ply search depths then would be 20 * 70 = 1400 elo
above.
Software improvements not counted!!!!!
Just search depth based elo!!!!!
It was the time of the superbeancounters.
Basically there was only 2 voices against the above lineair scaling.
That was Don and that was me.
Known experts against, that's a list so big i can keep typing. Most well known as he did write an article on it, that was Ernst A Heinz.
With something dubious as the number of fail highs that crafty would get at a bigger plydepth he hoped to prove this lineair scaling. Entire names got invented.
Don did do some tests to prove that lineair scaling didn't exist.
I designed the tactical barrier for that.
I've never done a hard formulation on what it was, but i intended with it several things.
a) basically the observation that in grandmaster chess most tactics is a ply or 12+ and players not giving away material, games get mostly decided then not by tactics, yet by chessknowledge, positional patterns and strategy.
In short the notion that above a certain search depth improving the evaluation function is more important than getting yet another ply.
This above explanation is what i posted most back then.
I think i twas Bob who led the pack attacking that. He attacked it by saying that under no circumstance a better evaluation function was worth more than or equal to 2 ply of additional search depth.
Online back then games of engines getting 6 ply versus opponents getting 8, that was not a contest. 8 ply always won.
That would lineair scale also to bigger search depths. I denied that.
Nowadays no one is busy with that, as 30 ply engines play 17 ply engines and the 17 ply sometimes wins (not much though), which in that eloscaling wold be impossible of course as 30 ply would be 13 * 70 = 910 elopoints stronger, which means that you have a hard 0% chance to ever win a game, as you just can't test enough games for that luck once as that would need to happen long after the Sun has become a supernova.
The next deduced interpretation of that tactical barrier is the notion of course, that once your program picks up a lot of tactics, that it becomes more important to search positional moves than ONLY tactical moves - again i don't mean to say you should ditch all tactics, i just say it's less relevant.
Please see that editted 'only'. As the notion of the 80s and 90s was to do something to ONLY see tactics and ONLY pick up tactics. In my interpretation, tactics is one positional aspect of the game, an important one, but not the only aspect. Not more important when we search that deep than STRATEGICAL considerations. In the end majority of tactics, just like other positional plans (such as trying to move a knight from f3 to d5 via a manoeuvre) that is short term plans. Strategy is a LONG term plan.
I hope i write that down in understandable manner; as the idea and notion of it is total derived from myself playing chess of course.
I also use this explanation to explain why for Diep futility doesn't really work. Let's start saying that futility needs a pretty narrow window. You can't do futility at 50 pawns, that's not so useful. If we do it however at say 1 pawn margin, then with diep's huge evaluation it's nearly impossible to predict which moves suddenly need to get evaluated lazy and which do not.
futility then effectively has the effect that it gets rid in quite some positions the best positional move(s) meanwhile not losing the tactical moves.
So at testsets that scores a lot more elopoints, yet in playing games it loses more games as it plays a lot weaker.
Now most beancounters here have a real simple evaluation, the few exceptions such as passers are easy to put in the lazy consideration;
that means that the odds you miss good positional moves suddenly
is very small and explains why futility works for them.
I argue that for such programs futility would also work without being combined with other forms of selectivity, such as bigger R's for nullmoves and/or bigger selectivity.
This to refute the criticism of Tord that one needs to go through a few hills and valleys in order to get it to work.
