Author: Andrew Wagner
Date: 05:47:38 03/15/04
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 - -
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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