Author: Bob Durrett
Date: 05:59:25 03/15/04
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On March 15, 2004 at 08:47:38, Andrew Wagner wrote: > I got to thinking last night. This is a very bad idea for people like me who >are not experienced at it. Folks, don't try this at home. So... what was I >thinking about? Thinking. Bear with me here folks, this is kind of a long post. > > > Computers and humans really think in quite opposite approaches. In classic >alphabeta, we start by generating all legal moves and throwing out the bad ones >until (hopefully) we have the one good one left. But of course no human thinks >like this. They start with NO moves, and use positional, tactical, and pattern >considerations to generate just a few possible good moves. Then for each of >those moves, they again generate just a few responses (rather than every legal >response as alphabeta would), and so on. > > Now, in one sense humans search much more efficiently than computers. Because >they don't look at ridiculous captures like queen takes pawn which is defended >by another pawn, they are saved a lot of time and effort. The flipside of this >is that computers are ABLE to look at millions of these ridiculous captures in >the time it takes a human to look at just a few moves. > > However, if you think about it, human searching can hardly be called efficient >most of the time. I mean really, for those of you who play, how often to you >calmly, coldly calculate your way through a tree like described above? We tend >to skip steps, jump around in our thinking, get distracted, and so on. > > So, the question becomes...What if a computer could codifiy that thinking >process, using existing techniques like pruning, extensions, hash tables, and so >on, to change the shape of the tree **based on positional considerations**. Let >me illustrate with a position here. >[d]r1b1q1k/pQp/2p1p3/p1PpP3/P2N1P1B/2P1R3/6PP/3n2K1 w - - [D]r1b1q1k/pQp/2p1p3/p1PpP3/P2N1P1B/2P1R3/6PP/3n2K1 w - - > >White has sacrificed a rook to reach this position, and now unleashes a surprise >queen sacrifice for mate in 6. Qxg7+ Kxg7 Bf6+ Kg6 Bg7+ Kh5 Rg5+ Kh4 Nf3#. > > So for any engine which has check extensions, this tactic should be easy, >right? But, how many times will check extensions prove to be a waste of time? I >mean, if the king is well-defended, it's silly to search a line where you >sacrifice all your pieces to break open the king, only to discover that you have >nothing left to mate him with. > > But in this position, it's easy to see that check extensions are called for. >Look at black's pieces. 4 of the 5 are on the first rank. Look at the center. >It's completely closed, making fast movement of pieces to defend the king >impossible, and white has more space. Look at white's pieces. They all point >menacingly towards the black king. If you're well-trained to look for it, it >should be easy to realize that some kind of sacrifice to drag the king into the >open should be considered. > > Many advances have been made in chess programming. We have some amazingly >sophisticated techniques and shortcuts. But we're still brute-forcing our way >through. Can't we instead start looking at the human thought process involved in >chess, and define it in terms of these different techniques? This way, rather >than simply trying every technique on a position and hoping one of them works >and offsets all the time wasted on inadequate techniques and silly lines, we >would have a toolkit to use, and can pick a tool based on the position, just >like humans do. > > Here are three ideas I had about how to "nail down" the way humans think: > > 1.) Show positions to a strong player, and have him say/write/type the first >thing that comes to his mind. This "inkblot" sort of approach, repeated many >times over, would give us some kind of indication as to what really the key >factors are in a position. > > 2.) During the course of a series of games, have a strong player (or two strong >players, playing each other) write down the first thing that comes to mind when >a move is made by his opponent. This could give us tremendous insight into move >ordering techniques. > > 3.) Take some classic books like Fine's Endgame book, or Vukovich's "Art >of Attack" and translate them into terms of search techniques like extensions >and pruning. > > > Now some may be thinking that these ideas would seem to be representative of >the classic brute-force approach. But what I'm really suggesting is not only >move-ordering, but move-list generation, based on positional considerations. Of >course, some brute-force will still be required, just to make sure everything is >tactically sound. But it seems to me that we are doing things backwards to use >brute force, and prune from there, instead of to "un-prune" some moves first, >and brute-force to see if we can beat that. > > One final thing: I realize that I'm a young, naive, beginner chess-programmer, >and suggesting these things is the equivalent of a 2-year-old questioning >newtonian physics. So please, don't bother informing me of this, I already know >it. I also realize that some or most of these ideas have probably been suggested >before. But if nothing else, I hope this leads to an interesting discussion on >why we do things the way we do. Thanks for reading, and I look forward to your >responses.
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